ISE MVJCE 2014-15

INFORMATION SCIENCE AND ENGINEERING

SEMESTER 8

10IS831-WIRELESS NETWORK AND MOBILE COMPUTING

Author Details:Name: Vanshika RastogiDesignation: Asst. ProfessorDepartment: ISE

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Unit 5

Mobile Client

1. Moving Beyond the Desktop Mobile devices have been classified as phones, pagers and Personal Data

Assistants (PDA). Initially, each of these devices had a specific role. Phones provided communication facility similar to wired phones. Pagers provided text messaging while the PDAs provided portable data

applications such as contacts, calendars, notes. With the evolving technology, these devices have merged and thus today we have

device integration. Today we have “one-size-fits-all” devices.

Time 1920-1960

1960-1970

1970-1980

1980-1990

1990-2000 2000-2010 and onwards

Devices Marine radio and vehicle-mounted telephone

Shoe phone

Briefcase cell phone

Bat mobile phone

First hand-held phone

NMT hand held

Nokia, Ericsson, Motorola handsets

Nokia Communicator Iphone, Nokia N97, Nokia E72, Blackberry, Samsung.

Carrier Technology

Analog Tecnology

IMTS Cellular Analog System

PCS/GSM GPRS/3G/UMTS/CDMA 3G/3.9G/4G/IMS/HSDPA/Mobile TV

Key Features Based on tubes, large and bulky, basic voice only device

Transistors allowed for miniaturization but still voice only

Cellular concepts were deployed but large heavy voice-only systems

GSM brought digital systems and limited data capability

Sleek, light weight digital systems, capable of carrying multimedia data

Sleek, high battery life, huge memory capacity, large secondary storage, 24X7 internet connected, camera

Fig. 5.1: Evolution of mobile technology

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2. A peek under the hood: Hardware Overview Today’s devices have the MIPS (Million Instructions per Second) capability to

process information stream. The various classes of devices primarily consists of:

a microprocessor a power source a signal converter an I/O unit some memory

Fig 5.2: Overview of a Digital Communication Device

There is a power supply unit (generally Lithium battery) that supplies power to all the components.

Processor is the brain of the device; it handles all processing with the memory and the Digital Signal Processor.

There is a RF to Digital converter that acts as an interface to the network.

3. Mobile Phones

Internally a cell phone consists of the following parts:

Antenna: the signal reception unit.

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Memory DS

ProcessorInput/output

Power Supply

RF to Digital

Antenna

Network

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Circuit Board: the control unit of the system. It has several chips mounted on it. The prominent among these are:

The analog-to-digital and digital-to-analog converter chips represented by the RF to digital block.

The microprocessor controls and coordinates the handset functions.

The ROM and flash memory chips provide storage for the phone’s storage requirements, which include system memory and application memory.

The DSP (Digital Signal Processor) manages the signal manipulation.

The Radio Frequency (RF) chip manages the signal channels while the power section is responsible for power management and recharging.

Display unit is the output unit, generally a LCD panel.

Keyboard

Microphone

Speaker

Battery

4. Features of Mobile Phone

Baseband functionality is helpful in providing provision of cellular control logic, signal processing and user interface management while also contributing to memory and energy management.

Baseband architecture in mobile phones is a group of tradeoffs between electromagnetic capability, performance, power consumption and cost.

Electromagnetic capability is determined by the placement of high speed circuits and RF transmitter locations along with other mechanical constructions.

Performance is calibrated in terms of user requirements, instructions processed per second and other system requirements.

Power consumption highly depends on the system activity.

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Cost is a function of number of components and their types or sizes, complexity involved and their integration and testing time.

Processor masters nearly all other individual functional components present in the set.

There can be a set of processors in the mobile phone as well like the Master Controller Unit (MCU), Digital Signal Processor (DSP), hardware processors, etc.

MCU is a general purpose processor that handles upper layers of cellular protocols.

For audio, hardware needs to be supportive of listening to different radio bands.

Audio hardware should also support polyphonic ringtones, speech manipulations suitable for different formats stereo music support.

For video/still images, hardware should at least have CMOS (Complementary Metal-Oxide Semiconductor) image sensors and optical lens assembly with logic.

There are various issues for video/image capture like:

Cost optimization with respect to resolution of the camera.

Dust protection and operating temperature.

Mechanical design of the camera.

Object mobility

Sensitivity limit with respect to available glare.

Noise.

The display in mobile phones, now support more than 65536 true colors.

The dominant technology today is LCD (Liquid Crystal Display).

5. PDA

PDA has a similar architecture as the desktops have.

They have a microprocessor, an I/O mechanism, memory and additionally a wireless or IR port, power source, generally a battery.

They have a Operating system and tries to mimic the applications on the desktop.

These are considered to be the extension to the desktop.

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Microprocessor

It is the control unit, and is responsible for initiating and coordinating the PDA’s functions.

PDA’s use cheap low-end processors such as the Motorolla Dragonball.

The processors used are very basic but are sufficient for the requirements of the PDA.

The application developers have to ensure that they do not overload the processor, leading to processor degradation and poor performance.

Operating System

The OS has a lot of responsibilities here.

The OS used here are simple, with fewer instructions.

The major OS are, Palm OS, Symbian and Pocket PC.

Memory

PDA does not have any concept of hard drive.

It has a solid-state memory like Static RAM or flash memory.

It usually has a memory of about 2MB.

This is used to store the OS and application programs; these remain intact even when the machine shut downs.

The user data is stored in the RAM.

Battery

PDA’s uses rechargeable lithium, nickel-cadmium or nickel-metal hydride batteries that last for an average of two hours.

Batteries may drain because of :

Additional memory

Color LCD display

High-end features like voice recording, camera, MP3 players.

LCD Display

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LCD is used for both input and output.

The display may be grayscale (16) or color (65,536) has resolution of 160X160, 240X320, etc.

While backlight helps in better reading in the dark but consume more battery power.

Input Device-Buttons in combination with Touch-Screen or Keyboard

These devices use a stylus and touch screen in combination with a handwriting recognition program.

Most of them have buttons to bring up frequently used applications.

Input/Output ports

PDA must be able to communicate with a PC.

This communication is called data synchronization and is done through a serial or USB port.

6. Design Constraints in Applications for Handheld Devices

Processing Power

The processing speed starts at about 16MHz.

If everything is shifted to the server side, leads to poor performance.

Based on the functionality and specificity of the software, clients are of three types:

Thin clients: are similar to web browsers. These offers generality at the cost of bandwidth. This is important where the user pays for the data and not for the call time.

Thick clients: this resolves the bandwidth problem but introduces two new problems; the size of the application on the device and distribution of the application when an update or fix happens.

Thin plus or semi-thick clients: how thick or thin is decided based on the functionality of the application, the bandwidth availability and cost constraints.

Screen Size

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Most handheld devices have a small screen size, limiting to the information that can be displayed.

A general rule of thumb is that the depth of navigation should be atmost four clicks.

Cumbersome Input Devices

Most devices sport a stylus or T keypads or a small “qwerty” keypad where keying in long strings is a pain.

Hence input should be kept to minimum.

Application load time

The load time for any application should be very low, as users woul not like to wait for getting the application loaded.

Battery

One of the key to success of the application is battery life.

A service that utilizes more CPU consumes more power.

Memory

All devices have a limited storage space.

External memory can be used with the devices.

Data Storage

All devices provide some amount of persistent storage.

Different devices organize data in different ways.

Backend Compatibility

Applications should be written in a manner that they may run on all the versions of the device.

Application Size

Applications need to be stored on the device.

Most of the devices will have an upper limitation on the size of the executables.

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7. Mobile IP: Intrduction

Why not to use a mobile computer in the internet???

Reason: you will not receive any packet as soon as you leave your home network.

The reason for this is the routing mechanism,

The host sends an IP packet with a header containing destination address and other fields.

The destination address determines the receiver of the packet and also determines the subnet of the receiver.

Routers look at the destination address and forward the packet according to the internal look-up table.

As long as the receiver can be reached within its physical subnet it gets the packets; as soon as it is out of the subnet, it will not receive any packet.

A solution to this could be to assign to the computer a new topologically correct IP address.

So, moving to a new location mean assigning a new IP address.

Problem with this is that no one is aware of this new address.

The next solution could be dynamically adapting the IP address with respect to the current location.

The problem is that the Domain Name System (DNS) needs some time before it updates the internal tables necessary to map a logical to an IP address.

This fails when mobile node is continuously on the move.

Since, the quick solutions failed, there is a need of a generally architecture.

Several requirements accompanied to the development of the standard:

Compatibility: a new standard can not introduce changes for applications or network protocols already in use. Mobile IP has to be integrated into an existing operating system or at least work with them. Mobile IP must not require special media or MAC/LLC protocols. It has to ensure that users can still access all the other servers and systems in the internet.

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Transparency: mobility should remain ‘invisible’ for many higher layer protocols and applications.

Scalability and efficiency: enhancing IP for mobility must not generate too many new messages flooding the whole network. Special care has to be taken considering the lower bandwidth of wireless links.

Security: all the messages related to Mobile IP should be authenticated.

Entities and Terminology

Mobile Node (MN): an end-system or router that can change its point of attachment to the internet using Mobile IP. The MN keeps its address and can communicate with any other system in the internet as long as link-layer connectivity is given.

Correspondent Node (CN): a partner is needed for any communication. CN is that partner.

Home Network: subnet the MN belongs to with respect to its IP address.

Foreign Network: current subnet the MN visits and which is not the home network.

Foreign Agent: FA provides several services to the MN during its visit to the foreign network

Care-of-Address: the current location of the MN from an IP point of view.

Home Agent: provides several services to the MN and is located in the home network.

IP Packet Delivery

CN want to send an IP packet to the MN.

CN does not need to know anything about the MN’s current location and sends the packet to IP address of the MN.

i.e. CN sends the packet to MN with destination as address of MN and source as address of CN.

The internet does not have any information regarding the location of MN.

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It routes the packet to the router responsible for the home network of the MN.

The HA intercepts the packet, knowing that MN is currently not in the home network.

The packet is not forwarded to the subnet as usual, but encapsulated and tunneled to the COA.

A new header is putted now, with COA as the destination address and HA as the source address.

The foreign agent decapsulates the packet; i.e. removes the additional header.

Forwards the packet with CN as source and MN as destination to the MN.

For the MN, mobility is not visible.

It receives the packet with the same sender and the receiver, as it would have been done in the home network.

8. Agent Discovery

One initial problem of MN after moving is how to find a foreign agent?

For this purpose, Mobile IP describes two methods:

Agent Advertisement

Foreign agents and home agents advertise their presence periodically using special advertisement messages.

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For the advertisement, Internet Control Message Protocol (ICMP) messages with some mobility extension.

The type is set to 9, the code can be 0, if the agent also routes traffic from non-mobile nodes, or, 16, if it does not route anything other than mobile traffic.

The number of addresses advertised with this packet is in #addresses.

Lifetime denotes the length of time this advertisement is valid.

Preference level for each address help a node to choose the router that is the most eager one to get a new node.

The mobility extension has the following fields;

Type is set to 16; length depends on the number of COAs provided with the message.

An agent shows the total number of advertisements sent since initialization in the sequence number.

By the registration lifetime the agent can specify the maximum lifetime in seconds.

The R bit (registration) shows, if a registration with this agent is required even when using a co-located COA.

If the agent is too busy to accept any new registration, it can set the B bit.

The bits H and F denote whether the agent is serving as a Home Agent or Foreign Agent.

Bits M and G specify the method of encapsulation used for the tunnel.

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Agent Solicitation

If no agent advertisement is present or the inter-arrival time is too high, and the MN has not received a COA by any means, it should send Agent Solicitation.

A MN can send three solicitations, one per second, as soon as it enters a new network.

If a node does not receive an answer to its solicitation, it must reduce the number of solicitation to flooding the system.

After these steps, the MN can now receive the COA.

9. Registration

Having received the COA, the MN has to register with the HA.

The main purpose of this registration is to inform the HA of the current location for correct forwarding of packets.

Registration can be done in two ways depending on the location of COA:

If the COA is at FA

HA sets up a mobility binding containing the MN’s home IP address and the current COA.

The mobility binding contains the lifetime of the registration.

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Registration expires automatically after the lifetime and is deleted; so the MN should register before expiration.

If the COA is co-located

Registration is simple.

The MN sends the registration request directly to the Home Agent.

This is also the registration procedure for the MN’s returning to their home network.

10.Tunneling

When a mobile node is registered with a home agent, the home agent must be able to intercept IP datagrams sent to the mobile node home address so that these datagrams can be forwarded via tunneling. T

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the standard does not mandate a specific technique for this purpose but references Address Resolution Protocol (ARP) as a possible mechanism.

The home agent needs to inform other nodes on the same network (the home network) that IP datagrams with a destination address of the mobile node in question should be delivered (at the link level) to this agent.

In effect, the home agent steals the identity of the mobile node in order to capture packets destined for that node that are transmitted across the home network.

To forward an IP datagram to a care-of address, the home agent puts the entire IP datagram into an outer IP datagram.

This is a form of encapsulation, just as placing an IP header in front of a TCP segment encapsulates the TCP segment in an IP datagram.

Three options for encapsulation are allowed for Mobile IP and we will review the first two of the following options:

IP-within-IP encapsulation: This is the simplest approach, defined in RFC 2003.

Minimal encapsulation: This approach involves fewer fields, defined in RFC 2004.

Generic routing encapsulation (GRE): This is a generic encapsulation procedure, defined in RFC 1701, that was developed prior to the development of Mobile IP.

In the IP-within-IP encapsulation approach, the entire IP datagram becomes the payload in a new IP datagram .

The inner, original IP header is unchanged except to decrement Time To Live (TTL) by 1.

The outer header is a full IP header. Two fields (indicated as unshaded in the figure) are copied from the inner header.

The version number is 4, the protocol identifier for IPv4, and the type of service requested for the outer IP datagram is the same as that requested for the inner IP datagram.

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11.Cellular IP

Mobile IP is optimized only for:

macro level mobility and

relatively slow moving hosts

Cellular IP is: new robust, simple, and flexible protocol for highly mobile hosts

CIP supports local mobility & efficiently interworks with Mobile IP

can accommodate large no. of users by separating idle from active hosts

requires no new packet formats, encapsulations, or address space allocations

Easy Global Migration

Cheap Passive Connectivity

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Efficient Location Management

Flexible Handoff

Simple Memory less Mobile hosts

Comparison with Mobile IP

Location management

a. Mobile IP: Care-of-address

b. Cellular IP: paging update packet

Routing

c. Mobile IP: registration

d. Cellular IP: routing cache

Handoff

e. Mobile IP: encapsulation, triangle routing

f. Cellular IP: routing cache

Cellular IP uses two parallel structures of mappings through Paging Caches (PC) and Routing Caches (RC).

PCs maintain mappings for stationary and idle hosts.

RC maintains mappings for mobile hosts.

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