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IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
COURSE MATERIAL IT6601-MOBILE COMPUTING
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
SYLLABUS (THEORY)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
L T P C 3 0 0 3
UNIT I INTRODUCTION 9 Mobile Computing ndash Mobile Computing Vs wireless Networking ndash Mobile Computing Applications ndashCharacteristics of Mobile computing ndash Structure of Mobile Computing Application MAC Protocols ndashWireless MAC Issues ndash Fixed Assignment Schemes ndash Random Assignment Schemes ndash Reservation Based Schemes UNIT II MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER 9 Overview of Mobile IP ndash Features of Mobile IP ndash Key Mechanism in Mobile IP ndash route Optimization Overview of TCPIP ndash Architecture of TCPIP- Adaptation of TCP Window ndash Improvement in TCP Performance UNIT III MOBILE TELECOMMUNICATION SYSTEM 9 Global System for Mobile Communication (GSM) ndash General Packet Radio Service (GPRS) ndashUniversal Mobile Telecommunication System (UMTS) UNIT IV MOBILE AD-HOC NETWORKS 9 Ad-Hoc Basic Concepts ndash Characteristics ndash Applications ndash Design Issues ndash Routing ndash Essential of Traditional Routing Protocols ndashPopular Routing Protocols ndash Vehicular Ad Hoc networks ( VANET) ndashMANET Vs VANET ndash Security UNIT V MOBILE PLATFORMS AND APPLICATIONS 9 Mobile Device Operating Systems ndash Special Constrains amp Requirements ndash Commercial Mobile Operating Systems ndash Software Development Kit iOS Android BlackBerry Windows Phone ndash M Commercendash Structure ndash Pros amp Cons ndash Mobile Payment System ndash Security Issues TOTAL 45 PERIODS
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TEXT BOOK
1 Prasant Kumar Pattnaik Rajib Mall ldquoFundamentals of Mobile Computingrdquo PHI Learning PvtLtd New Delhi ndash 2012
REFERENCES 1 Jochen H Schller ldquoMobile Communicationsrdquo Second Edition Pearson Education New Delhi2007 2 Dharma Prakash Agarval Qing and An Zeng Introduction to Wireless and Mobile systems Thomson Asia Pvt Ltd 2005 3 Uwe Hansmann Lothar Merk Martin S Nicklons and Thomas Stober ldquoPrinciples of Mobile Computingrdquo Springer 2003 4 WilliamCYLeeldquoMobile Cellular Telecommunications-Analog and Digital Systemsrdquo Second EditionTata Mc Graw Hill Edition 2006 5 CKToh ldquoAdHoc Mobile Wireless Networksrdquo First Edition Pearson Education 2002 6 Android Developers httpdeveloperandroidcomindexhtml 7 Apple Developer httpsdeveloperapplecom 8 Windows Phone Dev Center httpdeveloperwindowsphonecom 9 BlackBerry Developer httpdeveloperblackberrycom
SUBJECT IN-CHARGE HODCSE
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
COURSE OBJECTIVE
1 Understand the basic concepts of mobile computing
2 Be familiar with the network protocol stack
3 Learn the basics of mobile telecommunication system
4 Be exposed to Ad-Hoc networks
5 Gain knowledge about different mobile platforms and application development
COURSE OUTCOMES
1 Comprehend the basics of mobile Computing
2 Express the functionality of Mobile IP and Transport Layer
3 Classify different types of mobile telecommunication systems
4 Implement Adhoc networks with routing protocols
5 Use mobile operating systems in developing mobile applications
6 Synthesize new knowledge in the area of mobile computing by using
appropriate techniques
Prepared by Approved by Verified By STAFF NAME PRINCIPAL HOD (ABARVEEN)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT- I
INTRODUCTION
11 Mobile Computing Introduction
What is mobile Computing
bull What is mobile computing
Users with portable computers still have network connections while they move
bull A simple definition could be
Mobile Computing is using a computer (of one kind or another) while on the
move
12 Mobile Computing Vs wireless Networking
Mobile computing means communication services on the move Wireless
communication is the basis for mobile communication
Wireless network is classified in to two types
1) Fixed Infra structure Network
2) Adhoc Network
Fixed Infra structure Network Wireless device connects to the access point to
connect to the network ndash Access point acts as a hub to connect two wireless
devices
Adhoc Network Collection of wireless mobile nodes (devices) dynamically
forming a temporary network without the use of any existing network
infrastructure
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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MIETCSEIII YRMOBILE COMPUTING
UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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MIETCSEIII YRMOBILE COMPUTING
PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
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Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
SYLLABUS (THEORY)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
L T P C 3 0 0 3
UNIT I INTRODUCTION 9 Mobile Computing ndash Mobile Computing Vs wireless Networking ndash Mobile Computing Applications ndashCharacteristics of Mobile computing ndash Structure of Mobile Computing Application MAC Protocols ndashWireless MAC Issues ndash Fixed Assignment Schemes ndash Random Assignment Schemes ndash Reservation Based Schemes UNIT II MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER 9 Overview of Mobile IP ndash Features of Mobile IP ndash Key Mechanism in Mobile IP ndash route Optimization Overview of TCPIP ndash Architecture of TCPIP- Adaptation of TCP Window ndash Improvement in TCP Performance UNIT III MOBILE TELECOMMUNICATION SYSTEM 9 Global System for Mobile Communication (GSM) ndash General Packet Radio Service (GPRS) ndashUniversal Mobile Telecommunication System (UMTS) UNIT IV MOBILE AD-HOC NETWORKS 9 Ad-Hoc Basic Concepts ndash Characteristics ndash Applications ndash Design Issues ndash Routing ndash Essential of Traditional Routing Protocols ndashPopular Routing Protocols ndash Vehicular Ad Hoc networks ( VANET) ndashMANET Vs VANET ndash Security UNIT V MOBILE PLATFORMS AND APPLICATIONS 9 Mobile Device Operating Systems ndash Special Constrains amp Requirements ndash Commercial Mobile Operating Systems ndash Software Development Kit iOS Android BlackBerry Windows Phone ndash M Commercendash Structure ndash Pros amp Cons ndash Mobile Payment System ndash Security Issues TOTAL 45 PERIODS
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TEXT BOOK
1 Prasant Kumar Pattnaik Rajib Mall ldquoFundamentals of Mobile Computingrdquo PHI Learning PvtLtd New Delhi ndash 2012
REFERENCES 1 Jochen H Schller ldquoMobile Communicationsrdquo Second Edition Pearson Education New Delhi2007 2 Dharma Prakash Agarval Qing and An Zeng Introduction to Wireless and Mobile systems Thomson Asia Pvt Ltd 2005 3 Uwe Hansmann Lothar Merk Martin S Nicklons and Thomas Stober ldquoPrinciples of Mobile Computingrdquo Springer 2003 4 WilliamCYLeeldquoMobile Cellular Telecommunications-Analog and Digital Systemsrdquo Second EditionTata Mc Graw Hill Edition 2006 5 CKToh ldquoAdHoc Mobile Wireless Networksrdquo First Edition Pearson Education 2002 6 Android Developers httpdeveloperandroidcomindexhtml 7 Apple Developer httpsdeveloperapplecom 8 Windows Phone Dev Center httpdeveloperwindowsphonecom 9 BlackBerry Developer httpdeveloperblackberrycom
SUBJECT IN-CHARGE HODCSE
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
COURSE OBJECTIVE
1 Understand the basic concepts of mobile computing
2 Be familiar with the network protocol stack
3 Learn the basics of mobile telecommunication system
4 Be exposed to Ad-Hoc networks
5 Gain knowledge about different mobile platforms and application development
COURSE OUTCOMES
1 Comprehend the basics of mobile Computing
2 Express the functionality of Mobile IP and Transport Layer
3 Classify different types of mobile telecommunication systems
4 Implement Adhoc networks with routing protocols
5 Use mobile operating systems in developing mobile applications
6 Synthesize new knowledge in the area of mobile computing by using
appropriate techniques
Prepared by Approved by Verified By STAFF NAME PRINCIPAL HOD (ABARVEEN)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT- I
INTRODUCTION
11 Mobile Computing Introduction
What is mobile Computing
bull What is mobile computing
Users with portable computers still have network connections while they move
bull A simple definition could be
Mobile Computing is using a computer (of one kind or another) while on the
move
12 Mobile Computing Vs wireless Networking
Mobile computing means communication services on the move Wireless
communication is the basis for mobile communication
Wireless network is classified in to two types
1) Fixed Infra structure Network
2) Adhoc Network
Fixed Infra structure Network Wireless device connects to the access point to
connect to the network ndash Access point acts as a hub to connect two wireless
devices
Adhoc Network Collection of wireless mobile nodes (devices) dynamically
forming a temporary network without the use of any existing network
infrastructure
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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MIETCSEIII YRMOBILE COMPUTING
I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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MIETCSEIII YRMOBILE COMPUTING
directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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MIETCSEIII YRMOBILE COMPUTING
Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
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MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
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MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
TEXT BOOK
1 Prasant Kumar Pattnaik Rajib Mall ldquoFundamentals of Mobile Computingrdquo PHI Learning PvtLtd New Delhi ndash 2012
REFERENCES 1 Jochen H Schller ldquoMobile Communicationsrdquo Second Edition Pearson Education New Delhi2007 2 Dharma Prakash Agarval Qing and An Zeng Introduction to Wireless and Mobile systems Thomson Asia Pvt Ltd 2005 3 Uwe Hansmann Lothar Merk Martin S Nicklons and Thomas Stober ldquoPrinciples of Mobile Computingrdquo Springer 2003 4 WilliamCYLeeldquoMobile Cellular Telecommunications-Analog and Digital Systemsrdquo Second EditionTata Mc Graw Hill Edition 2006 5 CKToh ldquoAdHoc Mobile Wireless Networksrdquo First Edition Pearson Education 2002 6 Android Developers httpdeveloperandroidcomindexhtml 7 Apple Developer httpsdeveloperapplecom 8 Windows Phone Dev Center httpdeveloperwindowsphonecom 9 BlackBerry Developer httpdeveloperblackberrycom
SUBJECT IN-CHARGE HODCSE
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
COURSE OBJECTIVE
1 Understand the basic concepts of mobile computing
2 Be familiar with the network protocol stack
3 Learn the basics of mobile telecommunication system
4 Be exposed to Ad-Hoc networks
5 Gain knowledge about different mobile platforms and application development
COURSE OUTCOMES
1 Comprehend the basics of mobile Computing
2 Express the functionality of Mobile IP and Transport Layer
3 Classify different types of mobile telecommunication systems
4 Implement Adhoc networks with routing protocols
5 Use mobile operating systems in developing mobile applications
6 Synthesize new knowledge in the area of mobile computing by using
appropriate techniques
Prepared by Approved by Verified By STAFF NAME PRINCIPAL HOD (ABARVEEN)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT- I
INTRODUCTION
11 Mobile Computing Introduction
What is mobile Computing
bull What is mobile computing
Users with portable computers still have network connections while they move
bull A simple definition could be
Mobile Computing is using a computer (of one kind or another) while on the
move
12 Mobile Computing Vs wireless Networking
Mobile computing means communication services on the move Wireless
communication is the basis for mobile communication
Wireless network is classified in to two types
1) Fixed Infra structure Network
2) Adhoc Network
Fixed Infra structure Network Wireless device connects to the access point to
connect to the network ndash Access point acts as a hub to connect two wireless
devices
Adhoc Network Collection of wireless mobile nodes (devices) dynamically
forming a temporary network without the use of any existing network
infrastructure
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
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MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
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MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
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MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
COURSE OBJECTIVE
1 Understand the basic concepts of mobile computing
2 Be familiar with the network protocol stack
3 Learn the basics of mobile telecommunication system
4 Be exposed to Ad-Hoc networks
5 Gain knowledge about different mobile platforms and application development
COURSE OUTCOMES
1 Comprehend the basics of mobile Computing
2 Express the functionality of Mobile IP and Transport Layer
3 Classify different types of mobile telecommunication systems
4 Implement Adhoc networks with routing protocols
5 Use mobile operating systems in developing mobile applications
6 Synthesize new knowledge in the area of mobile computing by using
appropriate techniques
Prepared by Approved by Verified By STAFF NAME PRINCIPAL HOD (ABARVEEN)
Sub Code IT6601 BranchYearSem CSEIIIVI Sub Name MOBILE COMPUTING Batch 2016-2020 Staff Name ABARVEEN Academic Year 2018-2019
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT- I
INTRODUCTION
11 Mobile Computing Introduction
What is mobile Computing
bull What is mobile computing
Users with portable computers still have network connections while they move
bull A simple definition could be
Mobile Computing is using a computer (of one kind or another) while on the
move
12 Mobile Computing Vs wireless Networking
Mobile computing means communication services on the move Wireless
communication is the basis for mobile communication
Wireless network is classified in to two types
1) Fixed Infra structure Network
2) Adhoc Network
Fixed Infra structure Network Wireless device connects to the access point to
connect to the network ndash Access point acts as a hub to connect two wireless
devices
Adhoc Network Collection of wireless mobile nodes (devices) dynamically
forming a temporary network without the use of any existing network
infrastructure
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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MIETCSEIII YRMOBILE COMPUTING
I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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MIETCSEIII YRMOBILE COMPUTING
Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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MIETCSEIII YRMOBILE COMPUTING
temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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MIETCSEIII YRMOBILE COMPUTING
Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
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MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
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MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT- I
INTRODUCTION
11 Mobile Computing Introduction
What is mobile Computing
bull What is mobile computing
Users with portable computers still have network connections while they move
bull A simple definition could be
Mobile Computing is using a computer (of one kind or another) while on the
move
12 Mobile Computing Vs wireless Networking
Mobile computing means communication services on the move Wireless
communication is the basis for mobile communication
Wireless network is classified in to two types
1) Fixed Infra structure Network
2) Adhoc Network
Fixed Infra structure Network Wireless device connects to the access point to
connect to the network ndash Access point acts as a hub to connect two wireless
devices
Adhoc Network Collection of wireless mobile nodes (devices) dynamically
forming a temporary network without the use of any existing network
infrastructure
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
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MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
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MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
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MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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MIETCSEIII YRMOBILE COMPUTING
27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
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MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
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MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
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58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Wired Networks Mobile Networks
High bandwidth Low bandwidth
Low bandwidth
variability
High bandwidth
Variability
Can listen on wire Hidden terminal
Problem
High power
machines
Low power machines
High resource
machines
Low resource
machines
need physical
access
need proximity
13 Applications for mobile computing
There are several applications for mobile computing including wireless
remote access by travelers and commuters point of sale stock trading
medical emergency care law enforcement package delivery education insurance
industry disaster recovery and management trucking industry intelligence
and military
Most of these applications can be classified into
Wireless and mobile access to the Internet
Wireless and mobile access to private Intranets
Wireless and Adhoc mobile access between mobile computers
14 Mobile Computing -Characteristics
Ubiquity
Anywhere
Anytime
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MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
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17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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MIETCSEIII YRMOBILE COMPUTING
I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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MIETCSEIII YRMOBILE COMPUTING
temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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MIETCSEIII YRMOBILE COMPUTING
44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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MIETCSEIII YRMOBILE COMPUTING
directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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MIETCSEIII YRMOBILE COMPUTING
Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
Location Awareness
Current location of the user can be found out using GPS (Global
positioning system)
Ex Personalized application to find car maintaining service Traffic
control application and Fleet management application when travelling by
car
Adaptation
Adjust the bandwidth fluctuation automatically without disturbing the user
Personalization
Services can be personalized according to the user need Some type of information
can be obtained from the specific source
15 Application Structure
The simple three tier architecture
Presentation tier
User interface request and response in a meaningful way Needs web browser and client program for transfer of information
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MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
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MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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MIETCSEIII YRMOBILE COMPUTING
25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
Application tier Logical decision and calculation is performed in this layer Get the information from the user and makes the decision Moves data between presentation and data layers This layer is implemented using JAVA NET services cold fusion etc Data tier Contains database in which information is stored and retrieved 16 Wireless MAC Protocols ndash Issues
The medium access control or media access control (MAC) layer is the
Lower sub layer of the data link layer (layer 2) of the seven-layer OSI model
Wireless Channel (Wireless medium) is shared among multiple neighboring
nodes
If more than one MS transmit at a time on the shared media a collision
occurs
How to determine which MS can transmit
Access Control protocols define rules for orderly access to the shared medium
It should have the following features
Fairness in sharing Maximize the utilization of the channel Support different types of traffic Should be robust for equipment failures and changing network condition There are two types of basic classification to avoid medium access problem
1) Contention protocols 2) Conflict-free protocols
Contention protocols
Contention protocols resolve a collision after it occurs or try to avoid it These
protocols execute a collision resolution protocol after each collision
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
Conflict-free protocols
Conflict-free protocols (eg TDMA FDMA and CDMA) ensure that a
collision can never occur
Hidden Terminal Problem
A hidden node is one that is within the range of the intended destination but out
Of range of sender
Node B can communicate with A and C both
A and C cannot hear each other
When A transmits to B C cannot detect the transmission using the carrier
sense mechanism
C falsely thinks that the channel is idle
If C transmits collision will occur at node B
Exposed Terminal Problem
bull An exposed node is one that is within the range of the sender but
out of range of destination
bull B sends to A C wants to send to D
bull C has to wait CS signals a medium in use
bull since A is outside the radio range of C waiting is not necessary
bull C is ldquoexposedrdquo to B
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MIETCSEIII YRMOBILE COMPUTING
17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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MIETCSEIII YRMOBILE COMPUTING
UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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MIETCSEIII YRMOBILE COMPUTING
Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
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MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
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UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
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Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
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MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
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MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
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MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
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MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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17 Fixed-assignment schemes
FDMA
FDMA is the process of dividing one channel or bandwidth into multiple
individual bands each for use by a single user Each individual band or channel
is big enough to hold the signal to be propagated
For full duplex communication each user is allotted two channel
One channel for sending the data (forward link) other channel for receiving the
data (reverse channel)When the channel is not in use no one is permitted to use
that channel
Advantages of FDMA
bull Channel bandwidth is relatively narrow (30 kHz)
bull FDMA algorithms are easy to understand and implement
bull Channel Operations in FDMA are simple
bull No need for network timing
bull No restriction regarding the type of baseband or type of modulation
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Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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MIETCSEIII YRMOBILE COMPUTING
DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
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MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
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MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using FDMA
If channel is not in use it sits idle No high channel utilization
The presence of guard bands
bull Need right RF filtering to reduce adjacent channel interference
bull Maximum bit rate per channel is fixed
TDMA ndash Time Division Multiple Access
FDMA ndash Frequency Division Multiple Access
CDMA ndash Code Division Multiple Access
TDMA
TDMA allocates each user a different time slot on a given frequency TDMA Divides each cellular channel into three time slots in order to increase the amount of data that can be carried Each user occupies a cyclically repeating time slot
All the nodes use the same channel but in different time given to them in Round Robin Fashion
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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MIETCSEIII YRMOBILE COMPUTING
temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
Advantages of TDMA
Flexible bit rate
bull No frequency guard band required
bull No need for precise narrowband fi lters
bull Easy for mobile or base stations to initiate and execute hands off
bull Extended battery life
bull It is very cheap
Disadvantages to using TDMA
Unused time slot is wasted So it will lead to less channel utilization Has a predefined time slot When moving from one cell site to other if all the time
slots in the moved cell are full the user might be disconnected
Multipath distortion
Code division Multiplexing Access CDMA
Many users can use the channel to send the data Collision can be avoided
using code Each user is allotted different codes when sending a data the users
can multiplex their data with the code and send the data in the same channelso
different users use the same channel at the same time by using the coding
technique The code can be generated by using a technique called m bit pseudo-
noise code sequenceby using m bits 2m codes can be obtained From these each
user can use one code
Advantages of CDMA
Many users of CDMA use the same frequency TDD or FDD may be used
bull Multipath fading may be substantially reduced because of large signal
bandwidth
bull No limit on the number of users
bull Easy addition of more users
bull Impossible for hackers to decipher the code sent
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MIETCSEIII YRMOBILE COMPUTING
Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
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MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
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UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
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MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
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MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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Disadvantages to using CDMA
As the number of users increases the overall quality of service decreases
bull Self-jamming
bull Near-Far- problem arises
18 Random Access Scheme
bull ALOHA
bull CSMA
Simple ALOHA
ldquoFree for allrdquo whenever station has a frame to send it sends
It does not check if the channel is free or not
Station listens for maximum RTT for an ACK
If no ACK re-sends frame
If two or more users send their packets at the same time a collision occurs
and the packets are destroyed it does not work well when many nodes are
ready to send
In pure ALOHA frames are transmitted at completely arbitrary times
Pure ALOHA Performance Vulnerable period for the shaded frame
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MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
IT6601 ndash MOBILE COMPUTING
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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MIETCSEIII YRMOBILE COMPUTING
I-TCP Indirect TCP for Mobile Hosts
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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MIETCSEIII YRMOBILE COMPUTING
UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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MIETCSEIII YRMOBILE COMPUTING
AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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MIETCSEIII YRMOBILE COMPUTING
As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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MIETCSEIII YRMOBILE COMPUTING
PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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MIETCSEIII YRMOBILE COMPUTING
UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
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Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
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Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
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Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
S=Ge-2G where S is the throughput (rate of successful transmissions) and G is
the offered load
bull S = Smax=12e = 0184 for G=05
Slotted Aloha
bull Divide time up into small intervals each corresponding to one packet
bull At the beginning of the time slot only data will be sent
bull It sends a signal called beacon frame All the nodes can send the data only
at the starting of the signal
bull This also does not work well if many nodes are there to send the data
bull Vulnerable period is halved
bull S = G e-G
bull S = Smax = 1e = 0368 for G = 1
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MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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MIETCSEIII YRMOBILE COMPUTING
The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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MIETCSEIII YRMOBILE COMPUTING
Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
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Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
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Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
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Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
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MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
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MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
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MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
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MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Carrier Sense Multiple Access (CSMA)
bull Station that wants to transmit first listens to check if another transmission
is in progress (carrier sense)
bull If medium is in use station waits else it transmits
bull Collisions can still occur
bull Transmitter waits for ACK if no ACK retransmit
Two types of Transmission
CSMACA
CSMACDCSMACA Protocol
bull If the channel is sensed as busy no station will use it until it goes free
bull If the channel is free the node can start transmitting the data
bull This is the basic idea of the Carrier Sense Multiple Access (CSMA)
protocol
bull There are different variations of the CSMA protocols
bull 1-persistent CSMA
bull No persistent CSMA
bull p-persistent CSMA
bull 1-persistent CSMA (IEEE 8023)
ndash If medium idle transmit if medium busy wait until idle then transmit
with p=1
ndash If collision waits random period and starts again
bull Non-persistent CSMA if medium idle transmit otherwise wait a
random time before re-trying
ndash Thus station does not continuously sense channel when it is in use
bull P-persistent when channel idle detected transmits packet in the first
slot with pif the channel is not idle wait for thr the probability(1-p)and
the sense the channel
CSMACD
bull CSMA with collision detection Stations can sense the medium
while transmitting
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
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TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
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Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
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The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
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MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
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MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
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Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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I-TCP Indirect TCP for Mobile Hosts
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I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
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I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
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MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
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UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
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MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
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Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
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Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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MIETCSEIII YRMOBILE COMPUTING
Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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MIETCSEIII YRMOBILE COMPUTING
Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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MIETCSEIII YRMOBILE COMPUTING
Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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MIETCSEIII YRMOBILE COMPUTING
Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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MIETCSEIII YRMOBILE COMPUTING
communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
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MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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MIETCSEIII YRMOBILE COMPUTING
temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
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is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
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MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
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MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
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MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
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MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
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MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)
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MIETCSEIII YRMOBILE COMPUTING
bull A station aborts its transmission if it senses another transmission is
also happening (that is it detects collision) in the same time
CSMACD Protocol
1 If medium idle transmit otherwise 2
2 If medium busy some time and then sense the medium again then transmit
with p=1
3 If collision detected transmit brief jamming signal and abort transmission
4 After aborting wait random time try again
Summary
CSMA (Carrier Sense Multiple Access)
Improvement Start transmission only if no transmission is
ongoing
CSMACA (CSMA with Collision Avoidance)
Improvement Wait a random time and try again when carrier is
quiet If still quiet then transmit
CSMACD (CSMA with Collision Detection)
Improvement Stop ongoing transmission if a collision is
detected
19 Reservation based scheme
CONCEPT
MACAW A Media Access Protocol for Wireless LANs is based on
MACA (Multiple Access Collision Avoidance) Protocol
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MIETCSEIII YRMOBILE COMPUTING
MACA
bull When a node wants to transmit a data packet it first transmit a
RTS (Request to Send) frame
bull The receiver node on receiving the RTS packet if it is ready to
receive the data packet transmits a CTS (Clear to Send) packet
bull Once the sender receives the CTS packet without any error it
starts transmitting the data packet
bull If a packet transmitted by a node is lost the node uses the binary
exponential back-off (BEB) algorithm to back off a random
interval of time before retrying
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MIETCSEIII YRMOBILE COMPUTING
MACAW
Variants of this method can be found in IEEE 80211 as DFWMAC
(Distributed Foundation Wireless MAC)
MACAW (MACA for Wireless) is a revision of MACA
bull The sender senses the carrier to see and transmits a RTS
(Request to Send) frame if no nearby station transmits a RTS
bull The receiver replies with a CTS (Clear to Send) frame
bull Neighbors
bull See CTS then keep quiet
bull See RTS but not CTS then keep quiet until the CTS is
back to the sender
bull The receiver sends an ACK when receiving a frame
bull Neighbors keep silent until see ACK
bull Collisions
bull There is no collision detection
bull The senders know collision when they donrsquot receive CTS
bull They each wait for the exponential back off time
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MIETCSEIII YRMOBILE COMPUTING
UNIT II
MOBILE INTERNET PROTOCOL AND TRANSPORT LAYER
21 Overview of Mobile IP
Mobile IP (or MIP) is an Internet Engineering Task Force
(IETF) standard communications protocol that is designed to allow mobile
device users to move from one network to another while maintaining a
permanent IP address
MOBILE IP Terminology
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Mobile Node (MN)
A system (node) that can change the point of attachment to the
network without changing its IP address The Mobile Node is a device such
as a cell phone personal digital assistant or laptop which has roaming
capabilities
Home Network
Home Network is the network of a mobile node where it gets its
original IP Address
Home Agent (HA)
bull Stores information about all mobile nodes and its permanent address
bull It maintains a location directory to store where the node moves
bull It acts as a router for delivering the data packets
Foreign Agent (FA)
ds the packet to the MN
Care-of Address (COA)
Care-of address is a temporary IP address for a mobile node
(mobile device) that helps message delivery when the device is connected
somewhere other than its home network The packet send to the home
network is sent to COA
COA are of two types
Foreign agent COA It is the static IP address of a foreign agent on a visited
network
Co-located COA Temporary IP address is given to the node visited the
new network by DHCP
Correspondent Node (CN)
Node communicating to the mobile node
Foreign Network
The foreign network is current subnet to which the mobile node is visiting
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MIETCSEIII YRMOBILE COMPUTING
Tunnel
It is the path taken by the encapsulated packets
22 Features of Mobile IP
Transparency
mobile end-systems keep their IP address
Continuation of communication after interruption of link
Compatibility
Compatible with all the existing protocols
Security
Provide secure communication in the internet
Efficiency and scalability
only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
World-wide support of a large number of mobile systems in
the whole Internet
23 Key Mechanism in Mobile IP
To communicate with a remote host a mobile host goes through three
phases
Agent discovery registration and data transfer
bull Agent Discovery A Mobile Node discovers its Foreign and Home Agents during its move bull Registration
The Mobile Node registers its current location with the Foreign Agent
and Home Agent during registration
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MIETCSEIII YRMOBILE COMPUTING
bull Tunneling
A Tunnel(like a pipe) is set up by the Home Agent to the care-of
address (current location of the Mobile Node on the foreign network) to
send the packets to the Mobile Node as it roams
PACKET DELIVERY
1) Agent discovery
A mobile node has to find a foreign agent when it moves away from its
home network To do this mobile IP describes two methods
Agent advertisement
Agent solicitation
Agent advertisement
The Home Agent and Foreign Agent advertise their services on the network
by using the ICMP Router Discovery Protocol (IRDP) The Mobile Node
listens to these advertisements to determine if it is connected to its home
network or foreign network
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MIETCSEIII YRMOBILE COMPUTING
Home agents and foreign agents broadcast advertisements at regular
intervals by using the packet format given below
Type 16 agent advertisement
Length depends on number of care-of addresses advertised
Sequence number Number of advertisement sent since the
agent was initialized
Lifetime Lifetime of advertisement
Address Number of address advertised in this packet
Addresses Address of the router
Registration Lifetime Maximum lifetime a node can ask during
registration
R Registration with this foreign agent is required (or another foreign agent
on this network) Even those mobile nodes that have already acquired a
care-of address from this foreign agent must reregister
B Busy
H home agent on this network
F foreign agent on this network
M minimal encapsulation
G This agent can receive tunneled IP datagrams that use Generic Routing
Encapsulation (GRE)
Y This agent supports the use of Van Jacobson header compression
Care-of address The care-of address or addresses supported by this agent
on this network
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MIETCSEIII YRMOBILE COMPUTING
Type 19 indicates that this is a prefix-length advertisement
Length N where N is the value of the Numb Address field in the ICMP
router advertisement portion of this ICMP message
Agent Solicitation If the MN doesnrsquot receive any advertisement by the
agent then the MN must ask its IP by means of solicitation
2) Registration
Mobile nodes when visiting a foreign network informs their home agent of
their current care-of address renew a registration if it expires
Diagram
The mobile node when travels to the foreign network and gets the care of
address from the foreign network it has to inform this to the home network
This is done using the registration process
The process are
1) It first sends the registration request message to the foreign network This
is the registration process with the foreign network The registration request
message consists of mobile nodersquos Permanent IP Address and the home
agentrsquos IP address
2) The foreign agent will send the registration request message to the home
agent
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MIETCSEIII YRMOBILE COMPUTING
3) The home agent will store this information in its routing table This is
called mobility binding
4) The home agent then sends an acknowledgement to the foreign agent
5) The foreign agent passes this reply to the mobile node
6) The foreign agent updates its visitor list
3) Tunneling and encapsulation
This process forward IP datagram (packet) from the home
agent to the care-of address
Tunnel makes a virtual pipe for data packets between a tunnel
entry and a tunnel endpoint
Packets entering a tunnel travel inside the tunnel and comes out
of the tunnel without changing
When a home agent receives a packet for a mobile host it forwards
that packet to the care of address using IP-within-IP encapsulation
IP-in-IP encapsulation means the home a get inserts a new IP
header (COA address) added to the original IP packet
The new header contains HA address as source and Care of Address
as destination
Tunneling ie sending a packet through a tunnel is achieved by using
encapsulation
Encapsulation means taking a packet consisting of packet header and data
and putting it into the data part of a new packet
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MIETCSEIII YRMOBILE COMPUTING
The new header is also called the outer header for obvious reasons
Old header is called inner header There are three methods of
encapsulation
IP-in-IP encapsulation The figure shows the format of the packet
The packet consists of outer header and inner header
Outer header fields
The version field 4 for IP version 4
IHL DS (TOS) is just copied from the inner header
The length field covers the complete encapsulated packet
TTL must be high enough so the packet can reach the tunnel
endpoint
The next field here denoted with IP-in-IP is the type of the protocol
used in the IP payload This field is set to 4 the protocol type for IPv4
because again an IPv4 packet follows after this outer header
IP checksum is calculated as usual
The next fields are the tunnel entry as source address (the IP address
of the HA) and the tunnel exit point as destination address (the
COA)
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MIETCSEIII YRMOBILE COMPUTING
Inner header fields
It starts with the same fields as outer header The only change is TTL
which is decremented by 1 This means that the whole tunnel is considered
a single hop from the original packetrsquos point of view Finally the payload
follows the two headers
24 Route Optimization
Triangle Routing Tunneling forwards all packets go to home network (HA)
and then sent to MN via a tunnel
(CN-gtHNMN)
Two IP routes that need to be set-up one original and the
second the tunnel route
It causes unnecessary network overhead and adds Delay
Route optimization allows the correspondent node to learn the current
location of the MN and tunnel its own packets directly Problems arise with
Mobility correspondent node has to updatemaintain its cache
Authentication HA has to communicate with the
correspondent node to do authentication
Message transmitted in the optimized mobile IP are
1 Binding request
Correspondent Node (CN) sends a request to the home Agent to know
the current location of mobile IP
2 Binding Update
The Home agent sends the Address of the mobile node to CN
3 Binding Acknowledgement
The correspondent node will send an Acknowledgement after
getting the address from the HA
4 Binding Warning
When a correspondent node could not find the Mobile node it
sends a Binding Warning message to the HA
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DHCP
It is Dynamic Host Configuration Protocol
Administrator manually assigns the IP address to the system
Manual configuration is difficult and error-prone
Dynamic Host Configuration Protocol (DHCP) is used to configure IP
automatically
Using DHCP server
DHCP provides static and dynamic address allocation that can be manual
or automatic
In static allocation a DHCP server has a manually created static
database that binds
Physical addresses to IP addresses
Dynamic address allocation
The DHCP server maintains a pool (range) of available addresses This
address wil l be allocated to the system if it wants
1 A host which is joined newly in the network sends a DHCPDISCOVER
message to Broadcast IP address (255255255255) to all the server In
the fig given below two servers receive the broadcast message
2 Servers reply to the clientrsquos request with DHCPOFFER and offer a list of
configuration parameters Client can now choose one of the configurations
offered
3 The client in turn replies to the servers by accepting one of the
configurations and rejecting the others using DHCPREQUEST
4 If a server receives a DHCPREQUEST with a rejection it can free the
reserved configuration for other clients
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MIETCSEIII YRMOBILE COMPUTING
5 The DHCP server will say ok by giving a command called DHCPACK
6 The new system will take the new IP address assigned by the DHCP server
7 The addresses assigned from the pool are temporary addresses
8 The DHCP server issues that IP address for a specific time when the time
expires the client must renew it The server has the option to agree or
disagree with the renewal
9 If a client leaves a subnet it should release the configuration received by
the server using DHCPRELEASE Now the server can free the context
stored for the client and offer the configuration again
Origins of TCPIP
Transmission Control ProtocolInternet Protocol (TCPIP)
effort by the US Department of Defense
(DOD)
Advanced Research Projects Agency (ARPA)
inclusion of the TCPIP protocol with Berkeley UNIX (BSD UNIX)
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25 Overview of TCPIP
The TCPIP model explains how the protocol suite works to
provide communications
layers Application Transport Internetwork and Network Interface
Requests for Comments (RFCs)
describe and standardize the implementation and
configuration of the TCPIP protocol suite
26 TCPIP Architecture
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MIETCSEIII YRMOBILE COMPUTING
Application Layer
Protocols at the TCPIP Application layer include
File Transfer Protocol (FTP)
Trivial File Transfer Protocol (TFTP)
Network File System (NFS)
Simple Mail Transfer Protocol (SMTP)
Terminal emulation protocol (telnet)
Remote login application (rlogin)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Hypertext Transfer Protocol (HTTP)
Transport Layer Performs end-to-end packet delivery reliability and flow
control
Protocols
TCP provides reliable connection-oriented
communications between two hosts
Requires more network overhead
UDP provides connectionless datagram services between two hosts
Faster but less reliable
Reliability is left to the Application layer Ports
TCP and UDP use port numbers for communications between hosts
Port numbers are divided into three ranges
Well Known Ports are those from 1 through 1023
Registered Ports are those from 1024 through 49151
DynamicPrivate Ports are those from 49152 through 65535
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
TCP three-way handshake
Establishes a reliable connection between two points
TCP transmits three packets before the actual data transfer occurs
Before two computers can communicate over TCP they must
synchronize their initial sequence numbers (ISN)
A reset packet (RST) indicates that a TCP connection is to be terminated
without further interaction
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27 Adaption of TCP Window
TCP sliding windows
Control the flow and efficiency of communication
Also known as windowing
A method of controlling packet flow between hosts
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Allows multiple packets to be sent and affirmed with a
Single acknowledgment packet
The size of the TCP window determines the number of
acknowledgments sent for a given data transfer
Networks that perform large data transfers should use large window
sizes
TCP sliding windows (continued)
Other flow control methods include
Buffering
Congestion avoidance
Internetwork Layer
Four main protocols function at this layer
Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
ARP
A routed protocol
Maps IP addresses to MAC addresses
ARP tables contain the MAC and IP addresses of other devices on the
network
When a computer transmits a frame to a destination on the local
network
It checks the ARP cache for an IP to MAC Address mapping for the
destination node
ARP request
If a source computer cannot locate an IP to MAC address mapping in
its ARP table
It must obtain the correct mapping
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MIETCSEIII YRMOBILE COMPUTING
ARP request (continued)
A source computer broadcasts an ARP request to all hosts on the
local segment
Host with the matching IP address responds this request
ARP request frame
See Figure 3-7
ARP cache life
Source checks its local ARP cache prior to sending packets on the
local network
ARP cache life (continued)
Important that the mappings are correct
Network devices place a timer on ARP entries
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MIETCSEIII YRMOBILE COMPUTING
ARP tables reduce network traffic
Reverse Address Resolution Protocol (RARP)
Similar to ARP
Used primarily by diskless workstations
Which have MAC addresses burned into their network cards but no IP
addresses
Clientrsquos IP configuration is stored on a RARP Server RARP request frame
RARP client Once a RARP client receives a RARP reply it configures its
IP networking components
By copying its IP address configuration information into its
local RAM
ARP and RARP compared
ARP is concerned with obtaining the MAC address of other clients
RARP obtains the IP address of the local host
ARP and RARP compared (continued)
The local host maintains the ARP table
A RARP server maintains the RARP table
The local host uses an ARP reply to update its ARP table and to send
frames to the destination
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The RARP reply is used to configure the IP protocol on the local host
Routers and ARP
ARP requests use broadcasts
Routers filter broadcast traffic
Source must forward the frame to the router
ARP tables
Routers maintain ARP tables to assist in transmitting frames from one
network to another
A router uses ARP just as other hosts use ARP
Routers have multiple network interfaces and therefore also include the
port numbers of their NICs in the ARP table
The Ping utility
Packet Internet Groper (Ping) utility verifies connectivity between two
points
Uses ICMP echo requestreply messages
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
The Trace utility
Uses ICMP echo requestreply messages
Can verify Internetwork layer (OSI-Network Layer) connectivity shows
the exact path a packet takes from the source to the destination
Accomplished through the use of the time-to-live (TTL) counter
Several different malicious network attacks have also been created using
ICMP messages
Example ICMP flood
Network Interface Layer
Plays the same role as the Data Link and Physical layers of the OSI
model
The MAC address network card drivers and specific interfaces for the
network card function at this level
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
No specific IP functions exist at this layer
Because the layerrsquos focus is on communication with the network
card and other networking hardware Assume congestion to be the primary
cause for packet losses and unusual delays
Invoke congestion control and avoidance algorithms resulting in
significant degraded end-to-end performance and very high interactive
delays
TCP in Mobile Wireless Networks Communication characterized by sporadic
high bit-error rates (10-4 to 10-6) disconnections intermittent connectivity due to
handoffs low bandwidth
Mobile Networks Topology
TCP Performance with BER
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Classification of Schemes
End-to-End protocols
loss recovery handled by sender
Link-layer solutions
hide link-related losses from sender
TCP sender may not be fully shielded
Split-connection approaches
hide any non-congestion related losses from TCP sender
since the problem is local solve it locally End-to-End Protocols
Make the sender realize some losses are due to bit-error not congestion
Sender avoid invoking congestion control algorithms if non-congestion
related losses occur
Eg Reno New-Reno SACK
Link-Layer Protocols Hides the characteristics of the wireless link from the
transport layer and tries to solve the problem at the link layer
Uses technique like forward error correction (FEC)
Snoop AIRMAIL(Asymmetric Reliable Mobile Access In Link-layer)
Pros
The wireless link is made more reliable
Doesnrsquot change the semantics of TCP
Fits naturally into the layered structure of network protocols
Cons
If the wireless link is very lousy sender times-out waiting for ACK and
congestion control algorithm starts Split Connection
Split the TCP connection into two separate connections
1st connection sender to base station
2nd connection base station to receiver
The base station simply copies packets between the connections in both
directions
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MIETCSEIII YRMOBILE COMPUTING
Pros
Sender shielded from wireless link
Better throughput can be achieved by fine tuning the wireless protocol link
Cons
Violates the semantics of TCP
Extra copying at the Base station
Classification of Schemes
28 Improving TCPIP Performance over Wireless Networks
Snoop-TCP
A (snoop) layer is added to the routing code at BS which keep track of packets in
both directions
Packets meant to MH are cached at BS and if needed retransmitted in the
wireless link
BS suppress DUPACKs sent from MH to FH
BS use shorter local timer for local timeout Changes are restricted to BS
and optionally to MH as well
E2E TCP semantics is preserved
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MIETCSEIII YRMOBILE COMPUTING
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MIETCSEIII YRMOBILE COMPUTING
I-TCP Indirect TCP for Mobile Hosts
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
I-TCP ndashLAN Performance
I-TCP ndashLAN Performance
Normal and overlapped ndash effective reaction to high BER Non-Overlapped ndash No congestion avoidance algorithm I-TCP ndashLAN Performance
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
I-TCP ndash WAN Performance Disadvantages End-to-end semantics is not followed MSR sends an ack to the correspondent but loses the packet to the mobile
host Copying overhead at MSR Conclusion I-TCP particularly suited for applications which are throughput intensive
Slow Start Sender starts by transmitting 1 segment On receiving Ack congestion window is set to 2 On receiving Acks congestion window is doubled Continues until Timeout occurs After thresh the sender increases its window size by [current window]on
receiving Ack(Congestion Avoidance phase)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Fast Recovery
After Fast retransmit perform congestion avoidance instead of slow start Why Duplicate ACK indicates that there are still data flowing between the two ends rarr Network resources are still available TCP does not want to reduce the flow abruptly by going into slow start
End to End Protocols Tahoe Original TCP Slow start Congestion avoidance fast retransmit Reno TCP Tahoe + Fast Recovery Significant Improvement - single packet loss Suffers when multiple packets are dropped New-Reno Reno + Stay in Fast Recovery The first non-duplicate ACK but not the expected one SACK Reno + SACK option When multiple packets are dropped Packet Loss Scenario Fast Retransmission ssthresh = 05 x current window size congestion window = 1 Reno New-Reno and SACK Fast Retransmission Fast Recovery congestion window = 05 x current window size +3 x segment size Increase window size by 1 on receiving a dup ACK
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT III
MOBILE TELECOMMUNICATION SYSTEM
Cellular Network Organization
Use multiple low-power transmitters (Base station) (100 W or less)
Areas divided into cells
Each served by its own antenna
Served by base station consisting of
transmitter receiver and control unit
Band of frequencies allocated
Cells set up such that antennas of all neighbors are equidistant
(Hexagonal pattern)
Cellular systems implements Space Division Multiplexing Technique
(SDM) Each transmitter is called a base station and can cover a fixed area called
a cell This area can vary from few meters to few kilometres
Mobile network providers install several thousands of base stations each
with a smaller cell instead of using power full transmitters with large cells
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Basic concepts
High capacity is achieved by limiting the coverage of each base station to
a small geographic region called a cell
Same frequencies timeslotscodes are reused by spatially separated base
station
A switching technique called handoff enables a call to proceed
uninterrupted when one user moves from one cell to another
Neighboring base stations are assigned different group of channels so as to
minimize the interference
By systematically spacing base station and the channels group may be
reused as many number of times as necessary
As demand increases the number of base stations may be increased thereby
providing additional capacity
Frequency Reuse
adjacent cells assigned different frequencies to
avoid interference or crosstalk
Objective is to reuse frequency in nearby cells
10 to 50 frequencies assigned to each cell
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
1 Higher capacity
Smaller the size of the cell more the number of concurrent userrsquos ie huge cells
do not allow for more concurrent users
2 Less transmission power
Huge cells require a greater transmission power than small cells
3 Local interference only
For huge cells there are a number of interfering signals while for small cells
there is limited interference only
4 Robustness
As cellular systems are decentralized they are more robust against the failure of
single components
Disadvantages
Infrastructure needed Cellular systems need a complex
infrastructure to connect all base stations
Handover needed The mobile station has to perform a handover
when changing from one cell to another
31 GSM ARCHITECTURE
GSM is a digital cellular system designed to support a wide variety of
services depending on the user contract and the network and mobile
equipment capabilities
formerly Group Special Mobile (founded 1982)
now Global System for Mobile Communication
GSM offers several types of connections
voice connections data connections short message service
There are three service domains
Bearer Services
Telematics Services
Supplementary Services
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MIETCSEIII YRMOBILE COMPUTING
311 GSM SERVICES AND FEATURES
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
Data Service (circuit
switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 1200 bits
Data service (packet switched)
synchronous 24 48 or 96 kbits
asynchronous 300 - 9600 bits
Tele Services
Telecommunication services helps for voice communication via mobile
phones
Offered voice related services
electronic mail (MHS Message Handling System implemented in
the fixed network)
ShortMessageServiceSMS
alphanumeric data transmission tofrom the mobile terminal using
the signaling channel thus allowing simultaneous use of basic
services and SMS (160 characters)
MMS
Supplementary services
Important services are
identification forwarding of caller number
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM
standard within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem) covers all radio aspects
NSS (network and switching subsystem) call forwarding
handover switching
OSS (operation subsystem) management of the network
313 GSM SYSTEM ARCHITECTURE
Winter 2001ICS 243E - Ch4 Wireless
Telecomm Sys
412
GSM elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN PSTN
RSS
radio cell
radio cell
MS
AUCOSS
signaling
O
GSM Network consists of three main parts
Radio subsystem RSS
Base Station Subsystem BSS
Network and Switching Subsystems NSS
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Radio subsystem
The Radio Subsystem (RSS) contains three main parts
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Mobile Stations (MS)
Base Transceiver Station (BTS) defines a cell and is responsible for radio
link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages radio
channel setup and handovers The BSC is the connection between the
Mobile Station and Mobile Switching Center
A mobile station (MS) is a hand portable and vehicle mounted unit
It contains several functional groups
SIM (Subscriber Identity Module)
personalization of the mobile terminal stores user parameters
PIN
IMEI
Cipher key
Location Area Identification
It also has Display loudspeaker microphone and programmable keys
Base Station Subsystem Consists of
Base Transceiver Station (BTS) defines a cell and is responsible for
radio link protocols with the Mobile Station
Base Station Controller (BSC) controls multiple BTSs and manages
radio channel setup and handovers The BSC is the connection between
the Mobile Station and Mobile Switching Center
Network and Switching Subsystems
It consists of
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitors Location Register (VLR)
Authentication Center (AuC)
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Mobile Switching Center (MSC) is the central component of the NSS
Its functions
Manages the location of mobiles
Switches calls
Manages Security features
Controls handover between BSCs
Resource management
Interworks with and manages network databases
Collects call billing data and sends to billing system
Collects traffic statistics for performance monitoring
Home Location Register (HLR)
Contains all the subscriber information for the purposes of call control and
location determination There is logically one HLR per GSM network
Visitors Location Register (VLR)
Local database for a subset of user data - data about all users currently visiting in
the domain of the VLR
Operation subsystem
The OSS (Operation Subsystem) used for centralized operation
management and maintenance of all GSM subsystems
The main Components of OSS are
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operation and Maintenance Center (OMC)
Authentication Center (AUC)
It is a protected database that stores the security information for each
subscriber (a copy of the secret key stored in each SIM)
Equipment Identity Register (EIR)
It contains a list of all valid mobile equipment on the network
Operation and Maintenance Center (OMC)
It has different control capabilities for the radio subsystem and the network
subsystem
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Radio spectrum is very limited resource and this is shared by all users Time- and
Frequency-Division Multiple Access (TDMAFDMA) is used to share the
frequency FDMA divides frequency bandwidth of the (maximum) 25 MHz into
124 carrier frequencies Each Base Station (BS) is assigned one or more carrier
frequencies
Time Division Multiple Access (TDMA) - the users take turns (in a round robin)
each one periodically getting the entire bandwidth for a little time
Frequency Division Multiple Access (FDMA) - the frequency spectrum is
divided among the logical channels with each user using some frequency band
Mobile unit can be in two modes
Idle - listening Dedicated sendingreceiving data
There are two kinds of channels Traffic channels (TCH) and Control channels
Organization of bursts TDMA frames and multi frames for speech and data
The fundamental unit of time in TDMA scheme is called a burst period and it
lasts 1526 msec Eight bust periods are grouped in one TDMA frame (12026
msec) which forms a basic unit of logical channels One physical channel is
one burst period per TDMA frame Traffic channels It is used to transmit data
It is divided to Full rate TCH and Half rate TCH
In GSM system two types of traffic channels used
Full Rate Traffic Channels (TCHF) This channel carries information at
rate of 228 Kbps
Half Rate Traffic Channels (TCHH) This channels carries information
at rate of 114 Kbps
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Control channels carries control information to enable the system to operate
correctly
1 BROADCAST CHANNELS (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
2 DEDICATED CONTROL CHANNELS (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
3 COMMON CONTROL CHANNELS (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
GSM Protocol
GSM architecture is a layered model used to allow communications
between two different systems The GMS protocol stacks diagram is shown
below
MS Protocols
GSM signaling protocol is divided in to three layers
Layer 1 The physical layer It uses the channel structures over the air
interface
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Layer 2 The data-link layer Across the Um interface the data-link layer
is LAP-D protocol is used Across Abs interface (LAP-Dm) is used Across
the A interface the Message Transfer Part (MTP) is used
Layer 3 GSM protocolrsquos third layer is divided into three sub layers
o Radio Resource Management (RR)
o Mobility Management (MM) and
o Connection Management (CM)
THIRD LAYER (RR MM AND CM)
The RR layer (radio resource) is the lower layer that manages both radio
and fixed link between the MS and the MSC The work of the RR layer is to
setup maintenance and release of radio channels
The MM layer is above the RR layer It handles the functions of the
mobility of the subscriber authentication and security and Location
management
The CM layer is the topmost layer of the GSM protocol stack This layer
is responsible for Call Control Supplementary Service Management and Short
Message Service Management call establishment selection of the type of service
(including alternating between services during a call) and call release
SECOND LAYER
To Signal between entities in a GSM network requires higher layers For
this purpose the LAPDm protocol is used at the Um interface for layer two
LAPDm is called link access procedure for the D-channel (LAPD LAPDm gives
reliable data transfer over connections sequencing of data frames and flow
control
PHYSICAL LAYER
The physical layer handles all radio-specific functions It multiplexes the
bursts into a TDMA frame synchronization with the BTS detection of idle
channels and measurement of the channel quality on the downlink
The physical layer at Um uses GMSK for digital modulation and performs
encryptiondecryption of data
The main tasks of the physical layer comprise channel coding and error
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MIETCSEIII YRMOBILE COMPUTING
detectioncorrection
It uses forward error correction (FEC) schemes
The GSM physical layer tries to correct errors but it does not deliver
erroneous data to the higher layer
The physical layer does voice activity detection (VAD)
CONNECTION ESTABLISHMENT
Mobile Terminated Call
1 call ing a GSM subscriber
2 forwarding call to GMSC
3 signal call setup to HLR
4 5 request MSRN from VLR
6 forward responsible MSC to GMSC
7 forward call to current MSC
8 9 get current status of MS
10 11 paging of MS
12 13 MS answers
14 15 security checks
16 17 set up connection
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MIETCSEIII YRMOBILE COMPUTING
Security in GSM
Security services
Access controlauthentication
User SIM (Subscriber Identity Module) secret
PIN (personal identification number)
SIM network challenge response method
Confidentiality
voice and signaling encrypted on the wireless link (after
successful authentication)
Anonymity
temporary identity TMSI (Temporary Mobile Subscriber
Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
A3 for authentication (ldquosecretrdquo open interface)
A5 for encryption (standardized)
A8 for key generation (ldquosecretrdquo open interface)
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AUTHENTICATION
Authentication key Ki the user identification IMSI and the algorithm
used for authentication A3 is stored in the sim This is known only to the MS
and BTS Authentication uses a challenge-response method The access
control AC (BTS) generates a random number RAND this is called as
challenge and the SIM within the MS reply with SRES (signed
response) This is called as SRES response
NW side
BTS send random number RAND to MS
MS side
MS prepares SRES response by giving the random number RAND and
Ki to the algorithm A8The output is the SRES which is sent to the BTS
BTS side
BTS also prepares the same SRES and the output from the MS is compared
with result created by the BTS
If they are the same the BTS accepts the subscriber otherwise the
subscriber is rejected
ENCRYPTION
To maintain the secrecy of the conversation all messages are encrypted
in GSM Encryption is done by giving the cipher key Kc with message to the
algorithm A5 Here the key is generated separately
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Kc is generated using the Ki which is stored in SIM and a random
number RAND given by BTS by applying the algorithm A8 Note that the SIM
in the MS and the network both calculate the same Kc based on the random value
RAND The key Kc itself is not transmitted over the air
MOBILITY MANAGEMENT
Handover or Handoff
Handover basically means changing the point of connection while
communicating
Whenever mobile station is connected to Base station and there is a need to
change to another Base station it is known as Handover
A handover should not cause a cut-off also called call drop handover
duration is 60 ms
There are two basic reasons for a handover
The mobile station moves out of the range The received signal level
decreases Error rate may increase all these effects may lower the
quality of the radio link
The traffic in one cell is too high and shift some MS to other cells with
a lower load (if possible) Handover may be due to load balancing
Four possible handover scenarios in GSM
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MIETCSEIII YRMOBILE COMPUTING
Intra-cell handover
Within a cell narrow-band interference could make transmission at
a certain frequency impossible
The BSC could then decide to change the carrier frequency (scenario
1)
Inter-cell intra-BSC handover
The mobile station moves from one cell to another but stays within
the control of the same BSC
The BSC then performs a handover assigns a new radio channel in
the new cell and releases the old one (scenario 2)
Inter-BSC intra-MSC handover
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As a BSC only controls a limited number of cells GSM also has to
perform handovers between cells controlled by different BSCs
This handover then has to be controlled by the MSC (scenario 3)
Inter MSC handover A handover could be required between two cells
belonging to different MSCs Now both MSCs perform the handover
together (scenario 4)
Whether to take handover or not
HD depends on the average value of received signal when MS moves away
from BT sold to another closer BTS new
BSC collects all values from BTS and MS calculates average values
Values are then compared with threshold (HO_MARGIN_ hysteresis to
avoid ping-pong effect)
Even with the HO_MARGIN the ping-pong effect may occur in GSM-a
value which is too high could cause too many handovers
Typical signal flow during an inter-bsc intra-msc handover
The MS sends its periodic measurements reports to BTS old the BTSold
forwards these reports to the BSC old together with its own measurements
Based on these values and eg on current traffic conditions the BSC old
may decide to perform a handover and sends the message HO_required to
the MSC
MSC then checks if the resources available needed for the handover from
the new BSC BSC new
This BSC checks if enough resources (typically frequencies or time slots)
are available and allocates a channel at the BTS new to prepare for the arrival
of the MS
The BTS new acknowledges the successful channel activation to BSC new
BSC new acknowledges the handover request
The MSC then issues a handover command that is forwarded to the MS
The MS now breaks its old connection and accesses the new BTS
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The next steps include the establishment of the link (this includes layer
two link
Establishment and handover complete messages from the MS)
the MS has then finished the handover release its old resources to the old
BSC and BTS
32 GPRS NETWORK ARCHITECTURE
GPRS is the short form of General Packet Radio Service It is mainly used
to browse internet in mobile devices GPRS is GSM based packet switched
technology It needs MS (mobile subscriber) or user to support GPRS network
operator to support GPRS and services for the user to be enabled to use GPRS
features
GPRS network Architecture
Entire GPRS network can be divided for understanding into following basic
GPRS network
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MIETCSEIII YRMOBILE COMPUTING
Serving GPRS Support Node (SGSN)- It is similar to MSC of GSM
network SGSN functions are outlined below
Data compression Authentication of GPRS subscribers VLR
Mobility management
Traffic statistics collections
User database
Gateway GPRS Support Node(GGSN)-
Packet delivery between mobile stations and external networks
Authentication
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Packet data is transmitted from a PDN via the GGSN and SGSN directly
to the BSS and finally to the MS
The MSC which is responsible for data transport in the traditional circuit-
switched GSM is only used for signaling in the GPRS scenario
Before sending any data over the GPRS network an MS must attach to it
following the procedures of the mobility management A mobile station must
register itself with GPRS network
GPRS attach
GPRS detach
GPRS detach can be initiated by the MS or the network
The attachment procedure includes assigning a temporal identifier called a
temporary logical link identity (TLLI) and a ciphering key sequence number
(CKSN) for data encryption
A MS can be in 3 states
IDLE
READY
STANDBY
In idle mode an MS is not reachable and all context is deleted
In the standby state only movement across routing areas is updated to the
SGSN but not changes of the cell
In the ready state every movement of the MS is indicated to the SGSN
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PROTOCOL ARCHITECTURE
Protocol architecture of the transmission plane for GPRS
All data within the GPRS backbone ie between the GSNs is transferred
using the GPRS tunneling protocol (GTP)
GTP can use two different transport protocols either the reliable TCP
(needed for reliable transfer of X25 packets) or the non-reliable UDP
(used for IP packets)
The network protocol for the GPRS backbone is IP (using any lower
layers)
Sub network dependent convergence protocol (SNDCP) is used
between an SGSN and the MS On top of SNDCP and GTP user packet
data is tunneled from the MS to the GGSN and vice versa
To achieve a high reliability of packet transfer between SGSN and MS a
special LLC is used which comprises ARQ and FEC mechanisms for PTP
(and later PTM) services
A base station subsystem GPRS protocol (BSSGP) is used to convey
routing and QoS-related information between the BSS and SGSN
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MIETCSEIII YRMOBILE COMPUTING
BSSGP does not perform error correction and works on top of a frame
relay (FR) network
Finally radio link dependent protocols are needed to transfer data over the
Um interface
The radio link protocol (RLC) provides a reliable link
33 UMTS (Universal Mobile Telephone System
bull Reasons for innovations
- new service requirements
- availability of new radio bands
bull User demands
- seamless Internet-Intranet access
- wide range of available services
- compact lightweight and affordable terminals
- simple terminal operation
- open understandable pricing structures for the whole
spectrum of available services
UMTS Basic Parameter
bull Frequency Bands (FDD 2x60 MHz)
ndash 1920 to 1980 MHz (Uplink)
ndash 2110 to 2170 MHz (Downlink)
bull Frequency Bands (TDD 20 + 15 MHz)
ndash 1900 ndash 1920 MHz and 2010 ndash 2025 MHz
bull RF Carrier Spacing
ndash 44 - 5 MHz
bull RF Channel Raster
ndash 200 KHz
bull Power Control Rate
ndash 1500 Cycles per Second
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UMTS W-CDMA Architecture
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UNIT 4
MOBILE AD HOC NETWORKS
HISTORICAL DEVELOPMENTS OF MANET
In early 1970s the Mobile Ad hoc Network (MANET) was called packet radio
network which was sponsored by Defense Advanced Research Projects Agency
(DARPA) They had a project named packet radio having several wireless
terminals that could communication with each other on battlefields ldquoIt is interesting
to note that these early packet radio systems predict the Internet and indeed were part
of the motivation of the original Internet Protocol suiterdquo
The whole life cycle of Ad hoc networks could be categorized into the First second and the third generation Ad hoc networks systems Present Ad
hoc networks systems are considered the third generation
The fi rst generation goes back to 1972 At the time they were called
PRNET (Packet Radio Networks) In conjunction with ALOHA (Arial
Locations of Hazardous Atmospheres) and CSMA (Carrier Sense Medium
Access) approaches for medium access control and a kind of distance-vector
routing PRNET were used on a trial basis to provide different networking
capabilities in a combat environment
The second generation of Ad hoc networks emerged in 1980s when the
Ad hoc network systems were further enhanced and implemented as a part of
the SURAN (Survivable Adaptive Radio Networks) program This
provided a packet-switched network to the mobile battlefield in an
environment without infrastructure This Program proved to be beneficial in
improving the radios performance by making them smaller cheaper and
resilient to electronic attacks
In the 1990s (Third generation) the concept of commercial Ad hoc networks arrived with notebook computers and other viable communication equipmentrsquos At the same time the idea of a collection of mobile nodes was Proposed at several researchers gatherings IEEE 80211
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
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MIETCSEIII YRMOBILE COMPUTING
Had adopted the term Ad hoc networks and the research community had
started to look into the possibility of deploying Ad hoc networks in other
areas of application
41 BASIC CONCEPTS OF MOBILE AD HOC NETWORKS
An Ad hoc network is a collection of mobile nodes which forms a
temporary network without the aid of centralized administration or standard
support devices regularly available as conventional networks These nodes
generally have a limited transmission range and so each node seeks the
assistance of its neighboring nodes in forwarding packets and hence the nodes
in an Ad hoc network can act as both routers and hosts Thus a node may
forward packets between other nodes as well as run user applications By
nature these types of networks are suitable for situations where either no fixed
infrastructure exists or deploying network is not possible Ad hoc mobile
networks have found many applications in various fields like mili tary
emergency conferencing and sensor networks Each of these application areas
has their specific requirements for routing protocols
Since the network nodes are mobile an Ad hoc network will typically
have a dynamic topology which wi l l have profound effects on
network characteristics Network nodes will often be battery powered which
limi ts the capacity of CPU memory and bandwidth This will require network
functions that are resource effective Furthermore the wireless (radio) media
will also affect the behavior of the network due to fluctuating link bandwidths
resulting from relatively high error rates These unique desirable features pose
several new challenges in the design of wireless Ad hoc networking protocols
Network functions such as routing address allocation authentication and
authorization must be designed to cope with a dynamic and volatile network
topology In order to establish routes between nodes which are farther than a
single hop specially configured routing protocols are engaged The unique
feature of these protocols is their ability to trace routes in spite of a dynamic
topology In the simplest scenarios nodes may be able to communicate directly
with each other for example when they are within wireless transmission
range of each other However Ad hoc networks must also support
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communication between nodes that are only indirectly connected by a series
of wireless hops through other nodes For example in Fig 31 to establish
communication between nodes A and C the network must enlist the aid of node
B to relay packets between them The circles indicate the nominal range of each
nodersquos radio transceiver Nodes A and C are not in direct transmission range of
each other since Arsquos circle does not cover C
Figure 31 A Mobil Ad hoc network of three nodes where nodes A and C
Must discover the route through B in order to communicate
In general an Ad hoc network is a network in which every node is
potentially a router and every node is potentially mobile The presence
of wireless communication and mobility make an Ad hoc network unlike
a traditional wired network and requires that the routing protocols used in an
Ad hoc network be based on new and different principles Routing protocols
for traditional wired networks are designed to support tremendous
numbers of nodes but they assume that the relative position of the nodes
will generally remain unchanged 42 CHARACTERSTICS OF MOBILE AD HOC NETWORKS
Characteristics of MANET
In MANET each node act as both host and router That is it is
autonomous in behavior
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Multi-hop radio relaying- When a source node and destination node for a
Message is out of the radio range the MANETs are capable of multi-hop
routing
Distributed nature of operation for security routing and host
configuration A centralized firewall is absent here
The nodes can join or leave the network anytime making the network
topology dynamic in nature
Mobile nodes are characterized with less memory power and light
weight features
The reliability efficiency stability and capacity of wireless links are
often inferior when compared with wired links This shows the
fluctuating link bandwidth of wireless links
Mobile and spontaneous behavior which demands minimum human
intervention to configure the network
All nodes have identical features with similar responsibilities and
capabilities and hence it forms a completely symmetric environment
High user density and large level of user mobility
Nodal connectivity is intermittent
The mobile Ad hoc networks has the following features-
Autonomous terminal Distributed operation Multichip routing
Dynamic network topology Fluctuating link capacity Light-
weight terminals
Autonomous Terminal
In MANET each mobile terminal is an autonomous node which may
function as both a host and a router In other words beside the basic processing
ability as a host the mobile nodes can also perform switching functions as a
router So usually endpoints and switches are indistinguishable in MANET
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Distributed Operation
Since there is no background network for the central control of the
network operations the control and management of the network is distributed
Among the terminals The nodes involved in a MANET should collaborate
amongst themselves and each node acts as a relay as needed to implement
functions like security and routing Multi hop Routing
Basic types of Ad hoc routing algorithms can be single-hop and multi hop
based on different l ink layer at tr ibutes and rout ing protocols Single-
hop MANET is simpler than multi hop in terms of structure and implementation
with the lesser cost of functionality and applicability When delivering data
packets from a source to its destination out of the direct wireless transmission
range the packets should be forwarded via one or more intermediate nodes
Dynamic Network Topology
Since the n o d e s are mobile the network topology may change rapidly
and predictably and the connectivity among the terminals may vary with time
MANET should adapt to the traffic and propagation conditions as well as the
mobility patterns of the mobile network nodes The mobile nodes in the network
dynamically establish routing among themselves as they move about forming
their own network on the fly Moreover a user in the MANET may not only
operate within the Ad hoc network but may require access to a public fixed
network (eg Internet)
Fluctuating Link Capacity
The nature of high bit-error rates of wireless connection might be more
profound in a MANET One end-to-end path can be shared by several sessions
The channel over which the terminals communicate is subjected to noise fading
and interference and has less bandwidth than a wired network In
some scenarios the path between any pair of users can traverse multiple
wireless links and the link themselves can be heterogeneous
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MIETCSEIII YRMOBILE COMPUTING
Light Weight Terminals
In most of the cases the MANET nodes are mobile devices with less
CPU processing capability small memory size and low power storage Such
devices need optimized algorithms and mechanisms that implement the
computing and communicating functions 43 APPLICATIONS OF AD HOC NETWORKS
Defense applications On-the-fly communication set up for soldiers on
the ground fighter planes in the air etc
Crisis-management applications Natural disasters where the entire
communication infrastructure is in disarray
Tele-medicine Paramedic assisting a victim at a remote location can
access medical records can get video conference assistance from a
surgeon for an emergency intervention
ele-Geo processing applications Combines geographical information
system GPS and high capacity MS Queries dependent of location
information of the users and environmental monitoring using sensors
Vehicular Area Network in providing emergency services and other
information in both urban and rural setup
Virtual navigation A remote database contains geographical
representation of streets buildings and characteristics of large metropolis
and blocks of this data is transmitted in rapid sequence to a vehicle to
visualize needed environment ahead of time
Education via the internet Educational opportunities on Internet to K-
12 students and other interested individuals Possible to have last-mile
wireless Internet access
A Vehicular Ad hoc Network [VANET] VANET is a form of Mobile Ad hoc network to provide communications among
nearby vehicles and between vehicles and nearby fixed equipment usually
described as roadside equipment The main goal of VANET is providing safety
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MIETCSEIII YRMOBILE COMPUTING
and comfort for passengers To this end a special electronic device will be placed
inside each vehicle which will provide Ad hoc Network connectivity for the
passengers This network tends to operate without any infrastructure or legacy
client and server communication Each vehicle equipped with VANET device
will be a node in the Ad hoc network and can receive and relay others messages
through the wireless network Collision warning road sign alarms and in-place
traffic view will give the driver essential tools to decide the best path along the
way There are also multimedia and internet connectivity facilities for passengers
all provided within the wireless coverage of each car Automatic Payment for
parking lots and toll collection are other examples of possibilities inside
VANET Most of the concerns of interest to MANETS are of interest in
VANETS but the details differ Rather than moving at random vehicles tend to
move in an organized fashion The interactions with roadside equipment can
likewise be characterized fair ly accurately And finally most vehicles
are restricted in their range of motion for example by being constrained to follow
a paved high way
Fig 35 A Vehicular Ad hoc Network
In addition in the year 2006 the term MANET mostly describes an
academic area of research and the term VANET perhaps its most promising
area of application In VANET or Intelligent Vehicular Ad hoc Networking
defines an intelligent way of using Vehicular Networking In VANET integrates
on multiple Ad hoc networking technologies such as WiFi IEEE 80211 bg
WiMAX IEEE 80216 Bluetooth IRA ZigBee for easy accurate effective and
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
simple communication between vehicles on dynamic mobility Effective
measures such as media communication between vehicles can be enabled as well
methods to track the automotive vehicles are also preferred In VANET helps in
defining safety measures in vehicles streaming communication between
vehicles infotainment and telematics Vehicular Ad hoc Networks are expected
to implement variety of wireless technologies such as Dedicated Short Range
Communications (DSRC) which is a type of WiFi Other candidate wireless
technologies are Cellular Satellite and WiMAX Vehicular Ad hoc Networks
can be viewed as component of the Intelligent Transportation Systems (ITS)
Wireless Sensor Networks
Advances in processor memory and radio technology will enable small
and cheap nodes capable of sensing communication and computation
Networks of such nodes called wireless sensor networks can coordinate
to perform distributed sensing of environmental phenomena
Sensor networks have emerged as a promising tool for monitoring (and
possibly actuating) the physical world util izing self-organizing networks of
battery-powered wireless sensors that can sense process and communicate A
sensor network] is a network of many tiny disposable low power devices called
nodes which are spatially distributed in order to perform an application-oriented
global task These nodes fo rm a network by communicating with each other
through the existing wired networks The primary component of the network is
the sensor essential for monitoring real world physical conditions such as sound
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temperature humidity intensity vibration pressure motion pollutants etc at
different locations
Wireless sensor networks can be considered as special case of mobile Ad
hoc networks (MANET) with reduced or no mobility Initially WSNs was
mainly motivated by military applications Later on the civilian application
domain of wireless sensor networks as shown in Fig 36 have been considered
such as environmental and species monitoring disaster management smart
home production and healthcare etc These WSNs may consist of
heterogeneous and mobile sensor nodes the network topology may be as simple
as a star topology the scale and density of a network varies depending on the
application Wireless mesh networks
Wireless mesh networks are Ad hoc wireless networks which are formed
to provide communication infrastructure using mobile or fixed nodesusers
The mesh topology provides alternative path for data transmission from the
source to the destination It gives quick re-configuration when the fi rstly chosen
path fails Wireless mesh network shou ld be capable o f se l f -
organization and se l f - maintenance The main advantages of wireless mesh
networks are high speed low cost quick deployment high scalability and high
availability It works on 24 GHz and 5 GHz frequency bands depending on
the physical layer used For example if IEEE 80211a is used the speed
can be up to 54 Mbps An application example of wireless mesh network
could be a wireless mesh networks in a residential zone which the radio
relay devices are built on top of the rooftops In this situation once one of the
nodes in this residential area is equipped with the wired link to the Internet
this node could be the gateway node Others could connect to the Internet
from this node Other possible deployments are highways business zones
and university campus
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44 DESIGN ISSUES OF MOBILE AD HOC NETWORKS
Ad hoc networking has been a popular field of study during the last few
years Almost every aspect of the network has been explored in one way or other
at different level of problem Yet no ultimate resolution to any of the problems
is found or at least agreed upon On the contrary more questions have arisen
The topics that need to be resolved are as follows
Scalability
Routing
Quality of service
Client server model shift Security
Energy conservation
Node cooperation
Interoperation
The approach to tackle above aspects has been suggested and possible
update solutions have been discussed [31] In present research work one of the
aspects ldquothe routingrdquo has been reconsidered for suitable protocol performing
better under dynamic condition of network Scalability
Most of the visionaries depicting applications which are anticipated to
benefit from the Ad hoc technology take scalability as granted Imagine for
example the vision of ubiquitous computing where networks can be of any
size However it is unclear how such large networks can actually grow Ad
hoc networks suffer by nature from the scalabi l i ty problems in
capaci ty To exemplif y this we may look into simple interference
studies In a non- cooperative network where Omni-directional antennas
are being used the throughput per node decreases at a rate 1radicN where N
is the number of nodes
That is in a network with 100 nodes a single device gets at most Approximately one tenth of the theoretical network data rate This problem
however cannot be fixed except by physical layer improvements such as
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MIETCSEIII YRMOBILE COMPUTING
directional antennas If the available capacity like bandwidth radiation pattern of
antenna sets some limits for communications This demands the formulation of
new protocols to overcome circumvents Route acquisition service location and
encryption key exchanges are just few examples of tasks that will require
considerable overhead as the network size grows If the scarce resources are
wasted with profuse control traffic these networks may see never the day dawn
Therefore scalability is a boiling research topic and has to be taken into account
in the design of solutions for Ad hoc networks
Routing
Routing in wireless Ad hoc networks is nontrivial due to highly dynamic Environment An Ad hoc network is a collection of wireless mobile nodes
dynamically forming a temporary network without the use of any preexisting
network infrastructure or centralized administration In a typical Ad hoc
network mobile nodes come together for a period of time to exchange
information While exchanging information the nodes may continue to move
and so the network must be prepared to adapt continually to establish routes
among themselves without any outside support Quality of Service
The heterogeneity o f e x i s t i n g I n t e r n e t a p p l i c a t i o n s h a s
c h a l l e n g e d network designers who have built the network to provide best-
effort service only Voice live video and file transfer are just a few
applications having very diverse requirements Qualities of Service (QoS)
aware solutions are being developed to meet the emerging requirements of
these applications QoS has to be guaranteed by the network to provide certain
performance for a given flow or a collection of flows in terms of QoS
parameters such as delay jitter bandwidth packet loss probability and
so on Despite the current research efforts in the QoS area QoS in Ad hoc
networks is still an unexplored area Issues of QoS in robustness QoS in
routing policies algorithms and protocols with multipath including
preemptive priorities remain to be addressed
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MIETCSEIII YRMOBILE COMPUTING
Client-Server Model Shift
In the Internet a network client is typically configured to use a server as
its partner for network transactions These servers can be found automatically or
by static configuration In Ad hoc networks however the network structure
cannot be defined by collecting IP addresses into subnets There may not be
servers but the demand for basic services still exists Address allocation name
resolution authentication and the service location itself are just examples of the
very basic services which are needed but their location in the network is
unknown and possibly even changing over time Due to the infrastructure less
nature of these networks and node mobility a different addressing approach may
be required In addition it is still not clear who will be responsible for managing
various network services Therefore while there have been vast
research initiatives in this area the issue of shift from the traditional client-
server model remains to be appropriately addressed
Security
A vital issue that has to be addressed is the Security in Ad hoc networks
Applications like Military and Confidential Meetings require high degree of
security against enemies and activepassive eavesdropping attacker Ad hoc
networks are particularly prone to malicious behavior Lack of any centralized
network management or certification authority makes these dynamicall y
changing wireless st ructures very vulnerable to in f i l t rat ion
eavesdropping interference and so on Security is often considered to be
the major roadblock in the commercial application Energy Conservation
Energy conservative networks are becoming extremely popular within the
Ad hoc networking research Energy conservation is currently being addressed
in every layer of the protocol stack There are two primary research topics
which are almost identical maximization of lifetime of a single battery
and maximization of the lifetime of the whole network The former is related
to commercial applications and node cooperation issues whereas the latter is
more fundamental for instance in mili tary environments where node cooperation
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
is assumed The goals can be achieved either by developing better batteries or
by making the network terminals operat ion more energy ef f ic ient
The f i rs t approach is likely to give a 40 increase in battery life in the near
future (with Li-Polymer batteries) As to the device power consumption the
primary aspect are achieving energy savings through the low power hardware
development using techniques such as variable clock speed CPUs flash
memory and disk spin down However from the networking point of view
our interest naturally focuses on the devices network interface which is
often the single largest consumer of power Energy efficiency at the network
interface can be improved by developing transmissionreception technologies
on the physical layer
Much research has been carried out at the physical medium access control
(MAC) and routing layers while little has been done at the transport and
application layers Nevertheless there is still much more investigation to be
carried out
Node (MH) Cooperation
Closely related to the security issues the node cooperation stands in the
way of commercial application of the technology To receive the corresponding
services from others there is no alternative but one has to rely on other peoplersquos
data However when differences in amount and priority of the data come into
picture the situation becomes far more complex A critical fi re alarm box should
not waste its batteries for relaying gaming data nor should it be denied access
to other nodes because of such restrictive behavior Encouraging nodes to
cooperate may lead to the introduction of billing similar to the idea suggested
for Internet congestion control Well-behaving network members could be
rewarded While selfish or malicious users could be charged higher rates Implementation
of any kind of billi ng mechanism is however very challenging These issues
are still wide open
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Interoperation
The self-organization of Ad hoc networks is a challenge when two
independently formed networks come physically close to each other This is
an unexplored research topic that has implications on all levels on the
system design When two autonomous Ad hoc networks move into same
area the interference with each other becomes unavoidable Ideally the
networks would recognize the situation and be merged However the issue
of joining two networks is not trivial the networks may be using different
synchronization or even different MAC or routing protocols Security also
becomes a major concern Can the networks adapt to the situation For
example a military unit moving into an area covered by a sensor network
could be such a situation moving unit would probably be using different
routing protocol with location information support while the sensor network
would have a simple static routing protocol Another important issue comes into
picture when we talk about all wireless networks One of the most important
aims of recent research on all wireless networks is to provide seamless
integration of all types of networks This issue raises questions on how the Ad
hoc network could be designed so that they are compatible with wireless LANs
3 Generation (3G) and 4G cellular networks
ISSUES TO BE CONSIDERED WHEN DEPLOYING MANET The following are some of the main routing issues to be considered when
Deploying MANETs Unpredictability of environment Unreliability of Wireless Medium Resource- Constrained Nodes
Dynamic Topology
Transmission Error
Node Failures
Link Failures
Route Breakages
Congested Nodes or Links
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Unpredictability of Environment Ad hoc networks may be deployed
in unknown terrains hazardous conditions and even hostile environments
where tampering or the actual destruction of a node may be imminent
Depending on the environment node failures may occur frequently Unreliability of Wire less Medium Communication through the
wireless medium is unreliable and subject to errors Also due to varying
environmental conditions such as h igh levels of electro-magnetic
inter ference (EMI) or inclement weather the quality of the wireless link may
be unpredictable Resource-Constrained Nodes Nodes in a MANET are typical ly
battery powered as well as limited in storage and processing capabilities
Moreover they may be situated in areas where it is not possible to re- charge
and thus have limited lifetimes Because of these limitations they must have
algorithms which are energy efficient as well as operating with limited
processing and memory resources The available bandwidth of the wireless
medium may also be limited because nodes may not be able to sacrifice the
energy consumed by operating at full link speed Dynamic Topology The topology in an Ad hoc network may change
constantly due to the mobility of nodes As nodes move in and out of range of
each other some links break while new links between nodes are created
As a result of these issues MANETs are prone to numerous types of faults
included
Transmission Errors The unreliabilit y of the wireless medium and the
unpredictabilit y of the environment may lead to transmitted packets being
Garbled and thus received packet errors Node Failures Nodes may fail at any time due to different types of hazardous
conditions in the environment They may also drop out of the network either
voluntarily or when their energy supply is depleted
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Link Failures Node failures as well as changing environmental conditions
(eg increased levels of EMI) may cause links between nodes to break Link
failures cause the source node to discover new routes through other links
Route Breakages When the network topology changes due to nodelink
failures andor nodelink additions to the network routes become out-of-date
and thus incorrect Depending upon the network transport protocol packets
forwarded through stale routes may either eventually be dropped or be delayed
Congested Nodes or Links Due to the topology of the network and the nature
of the routing protocol certain nodes or links may become over util ized ie
congested This will lead to either larger delays or packet loss
45 ROUTING PROTOCOLS
Collection of wireless mobile nodes (devices) dynamically forming a
temporary network without the use of any existing network infrastructure
or centralized administration
ndash useful when infrastructure not available impractical or expensive
ndash mili tary applications rescue home networking
ndash Data must be routed via intermediate nodes Proactive Routing Protocols
Proactive protocols set up tables required for routing regardless of any
traffic This protocol is based on a l ink -state algori thm Link-state
algorithms f lood their in format ion about neighbors periodical ly with
routing table
Ex Destination sequence distance vector (DSDV)
Advantage of proactive
QoS guaranteed
The routing tables reflect the current topology with a certain precision Disadvantage
erheads in lightly loaded networks
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MIETCSEIII YRMOBILE COMPUTING
Example of proactive Routing Destination sequence distance vector (DSDV) Destination sequence distance vector (DSDV) routing is the extension to
distance vector routing for ad-hoc networks
Concept
Each node exchanges routing table periodically with its neighbors
Changes at one node in the network passes slowly through the network
This create loops or unreachable regions within the network
DSDV now adds two things to the distance vector algorithm Sequence numbers Each routing advertisement comes with a sequence
Number Advertisements may propagate along many paths Sequence numbers
help to receive advertisements in correct order This avoids the loops that are in
distance vector algorithm
Damping changes in topology that are of short duration should not
destabilize the Routing
Advertisements about such short changes in the topology are therefore not
transmitted further A node waits without advertisement if these changes are
unstable Waiting time depends on the time between the first and the best
announcement of a path to a certain destination Next Hop number of nodes the source will jump to reach the Destination Metric Number of Hops to Destination Sequence Number Seq No of the last Advertisement Install Time when entry was made
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MIETCSEIII YRMOBILE COMPUTING
The routing table for N1 in Figure would be as shown in Table
Advantages Loop free
Low memory
Quick convergence REACTIVE PROTOCOLS Reactive protocols setup a path between sender and receiver only if there
is a need for communication
Ex
Dynamic source routing and ad-hoc on-demand distance vector AODV
Advantage
evices can utilize longer low-power periods
Disadvantages initial search latency caching mechanism is useful only when there is high mobility Dynamic source routing (DSR)
In DSDV all nodes maintain path to all other nodes
Due to this there is heavy traffic
To save Battery power DSR is used
DSR divides the routing into two separate problems
1) Route Discovery
2) Route Maintenance Route discovery A node discover a route to a destination one and only i f
it has to send something to this destination and there is currently no known route
Route maintenance If a node is continuously sending packets via a route it
has to maintain that route If a node detects problems with the current route
it has to find a different route
Working Principle If a node needs to discover a route it broadcasts a route request with a unique
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Identifier and the destination address as parameters
Node that receives a route request does the following 1) If the node has already received the request it drops the request packet 2) If the node finds its own address as the destination the request has reached
its target
3) Otherwise the node adds its own address in the route and broadcasts this
updated route request
When the request reaches the destination it can return the request packet
containing the list to the receiver using this list in reverse order
One condition for this is that the links work bi-directionally
The destination may receive several lists containing different paths from the
Sender It has to choose the shortest path
Route discovery
From N1 to N3 at time t1 1) N1 broadcasts the request (N1 id = 42 target = N3) to N2 and N4 1-a)N2 broadcasts ((N1 N2) id = 42 target = N3) to N3N5 N3 recognizes itself as target N5 broadcasts ((N1 N2 N5) id = 42 target = N3) to N3 and N4 N4 drops N5rsquos broadcast N3 recognizes (N1 N2 N5) as an alternatebut longer route
1-b) N4 broadcasts ((N1 N4) id = 42 target = N3) to N1N2 and N5 N1
N2 and
N5 drop N4rsquos broadcast packet because they received it already
2) N2 has to go back to the path from N3-gtN2-gtN1It is called reverse
forwarding(Symmetric link assumed)
Route Maintenance
After a route is discovered it has to be maintained until the node sends
packets through this route
If that node uses an acknowledgement that acknowledgement can be
considered for good route
The node can listen to the next node forwarding the packet in the route A node can ask for an acknowledgement if the data is successfully sent
Multicast routing with AODV Routing protocol
AODV is a packet routing protocol designed for use in mobile ad hoc
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
networks (MANET)
Intended for networks that may contain thousands of nodes
One of a class of demand-driven protocols The route discovery mechanism is invoked only if a route to a destination
is not known
Route requests
This Protocol finds out multicast routes on demand using a
broadcast route discovery mechanism When a node wishes to join the
multi cast group or it wants to send packets to the group it needs to find
a route to the group This is done using two messages RREQ and RR
EP
When a node wants to join a multicast group it
sends a route request (RREQ) message to the group Only the members of
the multicast group respond to the join RREQ If any nonmember receives
a RREQ it rebroadcast the RREQ to its neighbors But if the RREQ is not
a join request any node of the multicast group may respond
Figure 1 depicts the propagation of RREQ
Fig RREP Propagation
The important fields for RREQ are given as follows
Source address The address of the node which sends the data
Destination address The address of the multicast group that is the target
of the discovery
Join ndashflag if this is set then the node originating RREQ wants to join the
multicast tree If it is unset then the originator is a source of multi cast
transmission
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Pointers Every node sets up pointers to determine the reverse route in its routing table
when receiving a RREQ This entry is used later to pass on a response back to
the route requester This entry is not activated until or unless it gets multicast
activation message from the requester The responding node unicasts the route
response RREP (figure 2) back to the route requester after the completion of
necessary updates on it routing table Route reply
When a node receives a RREQ for a multicast route it first checks the
Join -flag in the message If the Join -flag is set then the node may answer
only if it is itself a member of the multicast tree and its sequence number for
this tree greater than the number in the RREQ If the Join -flag is not set then any node may answer Creation of the multicast tree
The first node that wants to join the multicast group selects itself as
the multicast group leader The reason of this node is to keep the count of
the sequence number that is given to the multicast group address
The group leader assigns the sequence number by sending periodic Group
Hello messages Group Hellos messages are used to distribute group
information
Message types
MAODV uses four different message types for creation of the
multi cast routing table These messages are
Route request (RREQ) Route reply (RREP) Multi cast activation (MACT)
Group hello (GRPH)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Control tables
MADV has a routing table for the multicast routes The entries in this
table have the following attributes
Multicast group IP address Multicast group leader IP address
Multicast group sequence number Next hop(s) Hop count to next
multicast group member Hop count to multicast group leader Each next hop entry has the following fields
Next hop IP address
Next hop interface Link
direction Activated flag
In addition a node may also keep a multicast group leader table which is
used to optimize the routing This has the following fields
Multicast group IP address
Group leader IP address Multicast activation
A single node may get multiple replies to the RREQ message It must
choose the best out of these to be used for the multicast tree creation For
This reason the node joining the group send the in red to the node having
greatest seq no and less distance This is done using MCAST message
The receiver of the MACT message updates its multicast routing table by
setting the source of the message as a next hop neighbor
The MACT message has four flags These are join prune grpld r and update
The join is used if the node wishes to join the tree p ru n e is for leaving the
tree The two other messages are used if the tree breaks and must be
repaired
Leaving the tree
The membership of the multicast group is dynamic Each node can join
or leave the group at any time The leaving of the tree is done by sending the
MACT message with the prune-flag set
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MIETCSEIII YRMOBILE COMPUTING
48 VEHICULAR AREA NETWORK (VANET)
Basic objective is to find some relevant local information such as close by
gas stations restaurants grocery stores and hospitals
Primary motivation is to obtain knowledge of local amenities
Hello beacon signals are sent to determine other vehicle in the vicinity
Table is maintained and periodically updated in each vehicle
Vehicle in an urban area move out relatively low speed of up to 56 kmhr
while
Speed varies from 56 kmhr to 90 kmhr in a rural region
Freeway-based VANET could be for emergency services such as
accident traffic-jam traffic detour public safety health conditions etc
Early VANET used 80211-based ISM band
75 MHz has been allocated in 5850 - 5925 GHz band
Coverage distance is expected to be less than 30 m and data rates of 500
kbps
FCC has allocated 7 new channels of in 902 - 928 MHz range to cover a
distance of up to 1 km using OFDM
It is relatively harder to avoid collision or to minimize interference
Slotted ALOHA does not provide good performance
Non-persistent or p-persistent CSMA is adopted
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MIETCSEIII YRMOBILE COMPUTING
49 SECURITY CHALLENGES IN MANET
Missing authorization facilities hinders the usual practice of distinguishing
nodes as trusted or non-trusted
Malicious nodes can advertise non-existent links provide incorrect link
state information create new routing messages and flood other nodes
with routing traffic
Attacks include active interfering leakage of secret information
eavesdropping data tampering impersonation message replay message
distortion and denial-of-service (DoS)
Encryption and authentication can only prevent external nodes from
disrupting the network traffic
Internal attacks are more severe since malicious insider nodes are protected with the networkrsquos security mechanism Disrupting Routing Mechanism by A Malicious Node
Changing the contents of a discovered route
Modifying a route reply message causing the packet to be dropped as
an invalid packet
Invalidating the route cache in other nodes by advertising incorrect paths
Refusing to participate in the route discovery process
Modifying the contents of a data packet or the route via which that data
packet is supposed to travel
Behaving normally during the route discovery process but drop data
packets causing a loss in throughput
Generate false route error messages whenever a packet is sent from a
source to a destination Attacks by A Malicious Node
Can launch DoS attack
A large number of route requests due to DoS attack or a large number
of broken links due to high mobility
Can spoof its IP and send route requests with a fake ID to the same
destination
Routing protocols like AODV DSDV DSR have many vulnerabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Authority of issuing authentication is a problem as a malicious node can
leave the network unannounced
Security Approaches
Intrusion Detection System (IDS)
Automated detection
Subsequent generation of an alarm
IDS is a defense mechanism that continuously monitors the
network for unusual activity and detects adverse activities
Capable of distinguishing between attacks originating from inside the
network and external ones
Intrusion detection decisions are based on collected audit data
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
UNIT V
MOBILE PLATFORMS AND APPLICATIONS
51 Mobile Device Operating Systems
Mobile Operating System Structure
JAVA ME Platform
Special Constrains amp Requirements
Commercial Mobile Operating Systems
Windows Mobile
Palm OS
Symbian OS
iOS
Android
Blackberry Operating system
an operating system
that is specifically designed to run on mobile devices such as mobile phones
smartphones PDAs tablet computers and other handheld devices
programs called application programs can run on mobile devices
include processor memory files and various types of attached devices such as
camera speaker keyboard and screen
and networks
Control data and voice communication with BS using different types of
protocols
A mobile OS is a software platform on top of which other programs called
application programs can run on mobile Devices such as PDA cellular phones
smart phone and etc
MIET ENGINEERING COLLEGE
(Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY ndash PUDUKKOTTAI ROAD TIRUCHIRAPPALLI ndash 620 007
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Features
Java ME Platform
J2ME platform is a set of technologies specifications and libraries developed
for small devices like mobile phones pagers and personal organizers
va ME was designed by Sun Microsystems It is licensed under GNU
General Public License Configuration it defines a minimum platform
including the java language virtual machine features and minimum class
libraries for a grouping of devices Eg CLDC
Profile it supports higher-level services common to a more specific class of
devices A profile builds on a configuration but adds more specific APIs to make
a complete environment for building applications Eg MIDP
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Java ME platforms are composed of the following elements
52 Special Constrains amp Requirements
Limited memory
Limited screen size
Miniature keyboard
Limited processing power
Limited battery power
Limited and fluctuating bandwidth of the wireless medium
Requirements
Support for specific communication protocol
Support for a variety of input mechanism
Compliance with open standard
Extensive library support
Support for integrated development environment
53 Commercial Mobile Operating Systems
Windows Mobile
Windows Mobile OS
Windows Mobile is a compact operating system designed for mobile devices and
based on Microsoft Win32
to manipulate their data
Edition) - designed specifically for
Handheld devices based on Win32 API
PDA (personal digital assistant) palmtop computer Pocket were original
intended platform for the Windows Mobile OS
For devices without mobile phone capabilities and those that included mobile
phone capabilities
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Palm OS
Palm OS is an embedded operating system designed for ease of use with a touch
screen-based graphical user interface
on a wide variety of mobile devices such as
smartphones barcode readers and GPS devices
-based processors It is designed as a 32-b
The key features of Palm OS
-tasking OS
but it does not expose
tasks or threads to user applications In fact it is built with a set of threads
that cannot be changed at runtime
higher) does support multiple threads but doesnrsquot
support creating additional processes by user applications Expansion support
This capability not only augments the memory and IO but also it facilitates
data interchanges with other Palm devices and with other non-Palm devices
such as digital cameras and digital audio players
synchronization with PC computers
Support of serial port USB Infrared Bluetooth and Wi-Fi connections
management)
applications to store calendar address and task and note entries accessible by
third-party applications
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Symbian OS Features
Multimedia
recording playback and streaming
and Image conversion
-oriented and component- based
-server architecture
-efficient inter process communication This
feature also eases porting of code written for other platforms to Symbian OS
A Hardware Abstraction Layer (HAL)
layer provides a consistent interface to hardware and supports device-
independency
s hard real-time guarantees to kernel and user mode threads
54 Software Development Kit
541 iPhone OS
Applersquos Proprietary Mobile
iOS is Applersquos proprietary mobile operating system initially developed for
iPhone and now extended to iPAD iPod Touch and Apple TV
ldquoiPhone OSrdquo in June 2010
renamed ldquoiOSrdquo
enabled for cross licensing it can only be used on Applersquos devices
The user interface of iOS is based on the concept of usage of multi touch gestures
is a UNIX based OS
iOS uses four abstraction layers namely the Core OS layer the Core
Services layer the Media layer and the Cocoa Touch layer
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
rsquos App store contains close to 550000 applications as of March
2012
is estimated that the APPs are downloaded 25B times til l now
version of iOS is released in 2007 with the mane lsquoOS Xrsquoand then in 2008
the first beta version of lsquoiPhone OSrsquo is released
mber Apple released first iPod Touch that also used this OS
iPad is released that has a bigger screen than the iPod and iPhone
Cisco owns the trademark for lsquoIOSrsquo
Apple licenses the usage of lsquoiOSrsquo from Cisco
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
542 Android
Google owns a trademark for Android ndash Googlersquos permission is necessary to
use Androidrsquos trademark
made an agreement with Android device
manufacturers (including Samsung and HTC) to collect fees from them
source code is available under Apache License version 20 The
Linux kernel changes are available under the GNU General Public License
version 2
Android is Linux based mobile OS for mobile devices such as Tablets and
Smartphones
in 2007 Google formed an Open Handset Alliance with 86 hardware
software and telecom companies Now this OS is being used by multiple device
manufacturers (Samsung Motorola HTC LG Sony etc) in their handsets
community has large number of developers preparing APPs
in Java environment and the APP store lsquoGoogle Playrsquo now has close to 450000
APPs among which few are free and others are paid
that as of December 2011 almost 10B APPs were downloaded
It is estimated that as of February 2012 there are over 300M Android devices and
approximately 850000 Android devices are activated every day
earliest recognizable Android version is 23 Gingerbread which supports
SIP and NFC
32) are released with focus on
Tablets This is mainly focused on large screen devices
Handset layoutsndashcompatible with different handset designs such as larger
VGA 2D graphics library 3D graphics library based
ndasha lightweight relational database is used for data storage
- DO UMTS Bluetooth Wi-Fi
LTE NFC amp ndashSMS MMS threaded text messaging and
Android Cloud To Device Messaging (C2DM)
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Google faced many patent lawsuits against Android such as by Oracle in 2006
that included patents US5966702 and US6910205
543 Blackberry OS
The first operating system launched by Research in Motion
(RIM the company behind BlackBerry)
-
Interface)
Blackberry OS Features
Gestures
Multi-tasking
Blackberry Hub
Blackberry Balance
Keyboard
Voice Control
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Key Terms in Blackberry OS
Process Management
ndash Microkernel
Advantages of Blackberry OS
It provides good security for data
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and
ratings help users find the right app
(in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
Yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
is opened you have to swipe
up to return to the main display
Android Software Development Kit a software development kit that
enables developers to create applications for the Android platform
e Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots Manage port‐forwarding set breakpoints and view
thread and process information directly from Eclipse
promotion Dedicated content channels and feature banners that
provide prime real estate to help distribute your app to the right users
discovery Universal search top lists social sharing reviews and ratings
help users find the right app
The Games app (in combination with Score loop) A specialized portal for
gaming allowing multiplayer social connections
Disadvantages of Blackberry OS
New operating system was introduced too late into the ever-growing market
yet to have as many apps available for purchase or download compared to
other phone in the market
Consumers have switched over to other devices made by Apple or Android
Once an application is opened you have to swipe up
to return to the main display
Android Software Development Kit
A software development kit that enables developers to create applications
for the Android platform
Android SDK includes sample projects with source code development
tools an emulator and required libraries to build Android applications
Dalvik a custom virtual machine designed for embedded use which runs on top
of a Linux kernel
Android SDK Environment
The Android Development Tools (ADT) plugin for Eclipse adds powerful
extensions to the Eclipse integrated development environment It allows you to
create and debug Android applications easier and faster
IT6601 ndash MOBILE COMPUTING
MIETCSEIII YRMOBILE COMPUTING
Advantages
inside the Eclipse
IDE For example ADT lets you access the many capabilities of the DDMS
tool take screenshots
Manage port‐forwarding set breakpoints and view thread and process
information directly from Eclipse
55 M- Commerce
M-commerce (mobile commerce)is the buying and selling of goods and
services through wireless handheld devices such as cellular telephone and
personal digital assistants (PDAs)Known as next- generation e-commerce m-
commerce enables users to access the Internet without needing to find a place
to plug in
-commerce which is based on the Wireless
Application Protocol (WAP) has made far greater strides in Europe where
mobile devices equipped with Web-ready micro-browsers are much more
common than in the United states
M-commerce can be seen as means of selling and purchasing of goods and
services using mobile communication devices such as cellular phones PDA s
etc which are able to connect to the Internet through wireless channels and
interact with e- commerce systems
-commerce can be referred to as an act of carrying- out transactions using a
wireless device
is understood as a data connection that results in the transfer of value in
exchange for information services or goods It can also be seen as a natural
extension of e-commerce that allows users to interact with other users or
businesses in a wireless mode anytimeanywhere
perceived to be any electronic transaction or information interaction
conducted using a mobile device and mobile network thereby guaranteeing
customers virtual and physical mobility which leads to the transfer of real or
perceived value in exchange for personalized location-based information
services or goods
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MIETCSEIII YRMOBILE COMPUTING
-commerce can also be seen and referred to as wireless commerce
It is any transaction with a monetary value that is conducted via a mobile
telecommunications network M-commerce can also be seen and referred to as
wireless commerce
any transaction with a monetary value that is conducted via a mobile
telecommunications network
access an IT-System whilst moving from one place to the other
using a mobile device and carry out transactions and transfer information
wherever and whenever needed to
Mobile commerce from the future development of the mobile telecommunication
sector is heading more and more towards value-added services Analysts
forecast that soon half of mobile operatorrsquos revenue will be earned through mobile
commerce
Consequently operators as well as third party providers will focus on value-
added-services To enable mobile services providers with expertise on different
sectors will have to cooperate
scenarios will be needed that meet the customerlsquos
expectations and business models that satisfy all partners involved
Generations
-1992 wireless technology
current wireless technology mainly accommodates text
3rd generation technology (2001-2005) Supports rich media
(Video clips)
faster multimedia display (2006-2010)
M-Commerce Terminology
Terminology and Standards
-based Global Positioning System
mdashhandheld wireless computer
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MIETCSEIII YRMOBILE COMPUTING
Application Protocol
mdashInternet-enabled cell phones with attached applications
56 M-Commerce Structure
57 Pros of M-Commerce
M-commerce is creating entirely new service opportunities such as payment
banking and ticketing transactions - using a wireless device
-commerce allows one-to-one communication between the business and
the client and also business-to-business communication
-commerce is leading to expectations of revolutionary changes in
business and markets
-commerce widens the Internet business because of the wide coverage by
mobile networks
Cons of M-Commerce
Mobile devices donrsquot have enough processing power and the developer has to be
careful about loading an application that requires too much processing Also
mobile devices donrsquot have enough storage space The developer has to be also
concerned about the size of his application in the due process of development
quite vulnerable to theft loss and corruptibility Security
solutions for mobile appliances must therefore provide for security under these
challenging scenarios
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58 Mobile Payment System
Mobile Payment can be offered as a stand-alone service
also be an important enabling service for other m-
commerce services (eg mobile ticketing shopping gamblinghellip)
-
friendly
service providers have to gain revenue from an m-commerce service The
consumer must be informed of
how much to pay options to pay the payment must
be made payments must be traceable
Customer requirements
consistent payment interface when making the
Purchase with multiple payment schemes like
Merchant benefits
-to-use payment interface development
Bank and financial institution benefits
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59 Security Issues
WAP Risks
WAP Gap
WTLS protects WAP as SSL protects HTTP
protocol to another information is
decrypted and re-encrypted recall the WAP Architecture
-encryption in the same process on the WAP
gateway Wireless gateways as single point of failure
Platform Risks Without a secure OS achieving security on mobile devices is
almost impossible
Memory protection of processes protected kernel rings
File access control Authentication of principles to resources
untrusted code
Does not differentiate trusted local code from untrusted code downloaded from
the Internet So there is no access control
-safe
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MIETCSEIII YRMOBILE COMPUTING
can be scheduled to be pushed to the client device without the userrsquos
knowledge
Theft or damage of personal information abusing userrsquos
authentication information maliciously offloading money saved on smart cards
Bluetooth Security
Bluetooth provides security between any two Bluetooth devices for user
protection and secrecy
authentication
encryption key length
allowed to have access service Y)
The device has been previously authenticated a link key is
stored and the device is marked as ldquotrustedrdquo in the Device Database
Untrusted Device The device has been previously authenticated link key is
stored but the device is not marked as ldquotrustedrdquo in the Device Database
Device No security information is available for this device This is
also an untrusted device Automatic output power adaptation to reduce the
Range exactly to requirement makes the system extremely difficult to eavesdrop
New Security Risks in M-Commerce Abuse of cooperative nature of ad-hoc
networks An adversary that compromises one node can disseminate false
routing information
A single malicious domain can compromise devices by
downloading malicious code
Users roam among non-trustworthy domains Launching attacks from
mobile devices with mobility it is difficult to identify attackers
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MIETCSEIII YRMOBILE COMPUTING
security at the lower layers only a stolen device can still be
trusted Problems with Wireless Transport Layer Security (WTLS) protocol
Server only certificate (Most Common)
-establishing connection without re-authentication
new Privacy Risks Monitoring
userrsquos private information
added services based on location awareness (Location-Based Services)