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Chapter 3 ProtocolsChapter 3 Protocols
ProtocolsProtocols
3.13.1 Open Systems
3.23.2 The Layered ModelThe Layered Model
3.33.3 TCP/IPTCP/IP
3.43.4 IP AddressIP Address
3.53.5 SubnetworkSubnetwork
Classful network
Chapter 3 Protocol
ProtocolsProtocols
Protocol is a set of rules and procedures for communicating. When you travel to other countries, you should know
the proper way to • meet
• greet
• communicate with the local people
When two computers communicate, they should speak the same language agree on the same rules of communication
Chapter 3 Protocol
3.1 Open Systems
An open system consists of standardised rules, and procedures
for manufacturers to follow in making their products.
standards are open to the public without costManufacturers need not purchase license, but their products have to conform with the standards
Chapter 3 Protocol
3.1.1 Proprietary Standards (1/3)
Proprietary standards products developed by a vendor no common agreement regarded as trade secret occurred in early stage of the computer industry
Chapter 3 Protocol
3.1.1 Proprietary Standards (2/3)
Bad implications of proprietary products: Expensive
because supply is controlled by the vendor
Users familiar with one proprietary product cannot easily switch to other products
Communication and data sharing are hindered the vendors use different protocolscross platform compatibilityIn networking, gateways are designed to solve this problem
Chapter 3 Protocol
3.1.1 Proprietary Standards (3/3)
Gateway is the interface between two networks using different
protocols translating protocols from one standard to another
e.g. the broadband router in a home network
Chapter 3 Protocol
3.1.2 The needs for an Open System
Open systems: created by people from academic and professional
organisations independent of vendors standards are open to the public without cost
Manufacturers need not purchase license, but their products have to conform with the standards
Chapter 3 Protocol
3.1.3 ISO and IEEE (1/2)
ISO (International Organisation for Standardisation) voluntary organisation has defined Open System Interconnection (OSI)
for networking modelseveral layers
Chapter 3 Protocol
3.1.3 ISO and IEEE (2/2)
IEEE (Institute of Electrical and Electronic Engineers) professional organisation
related to electricity has specified IEEE 802
Local Area Network (LAN) standards
year (1980) and month (February)
lower levels (hardware) of the OSI layered model
Chapter 3 Protocol
3.2 The Layered Model (1/4)
Layered model helps us to understand how a computer works.
Layered Model in Computer Systems
Chapter 3 Protocol
3.2 The Layered Model (2/4)
Layers Description
Layer 7 Application Provides interfaces for applications like Web browser and e-mail package to access network services
Layer 6 Presentation Handles data format for network communication, protocol conversion, data encryption etc.
Layer 5 Session Permits two parties to hold ongoing communications
Layer 4 Transport Segments long data into chunks, handles re-assembling of chunks into original data
Layer 3 Network Translates logical network address to physical MAC address, and vice versa.
Layer 2 Data Link Adds MAC addresses and error-checking information
Layer 1 Physical Converts bits into signals for outgoing messages and vice versa
Chapter 3 Protocol
3.2 The Layered Model (3/4)
Chapter 3 Protocol
3.2 The Layered Model (4/4)
Chapter 3 Protocol
3.2 The Layered Model
3.2.3 Data Flow in Layers
When a message is sent by a user, it goes down through a stack of protocol layers. information are added to the message by each layer
Then, signals are produced by the NIC and transmitted over the cable.
On reaching the destination, the message moves up the same stack of layers, information previously added are removed.
Finally, the recipient views the message as if it were sent directly.
Chapter 3 Protocol
3.2 The Layered Model
3.2.4 Networking Software and Protocols
Networking software handles the tasks of sending and receiving data passes data up and down the protocol layers not a single program multiple programs corresponding to the OSI model
Protocol stack or protocol suite the multiple programs corresponding to the OSI model e.g. TCP/IP
Chapter 3 Protocol
3.3 TCP/IP (1/2)
TCP/IP (Transmission Control Protocol/ Internet Protocol) is not a single protocol is a protocol stack or protocol suite
with a set of protocols Components of TCP/IP are
TCP IP SMTPTelnetFTP HTTP HTTPS UDP ARP
Chapter 3 Protocol
3.3 TCP/IP (2/2)
TCP responsible for
breaking a message into packets re-assembling them at the destinationre-sends packets which have errors during transmission.
IP operates at a level just below TCP
adding and removing the IP addresses used in packets routing packets through the network.
Chapter 3 Protocol
3.3 TCP/IP
3.3.2 Pros and Cons of TCP/IP (1/2)
The advantages of TCP/IP are: Avoiding monopolisation by certain users. Even distribution of load between channels. If part of the network fails, communication can go on. The entire messages is guaranteed to be transmitted.
If a packet is not received properly, the receiver computer would request for re-transmission.
Allowing computers of different hardware and software to communicate
Chapter 3 Protocol
3.3 TCP/IP
3.3.2 Pros and Cons of TCP/IP (2/2)
The major disadvantage of TCP/IP is not designed for transmitting real-time signals,
like live voice or video.
packets may arrive out of sequence and or got lost impossible to re-transmit real-time signalsquality suffers
Solved by Quality of Service (QoS) allowing traffic to be prioritized
Chapter 3 Protocol
3.4 IP address (1/2)
IP address is is unique identifier of
computers, and some connecting devices, e.g. routers
is logical (compare with MAC address which is physical) is 32 bits (4 bytes) long
resulting in 4.3 billion (232 ~ 4.3 × 109) addresses theoretically.
4 numbers from 0 to 255, separated by periods• e.g. 202.148.153.49
Chapter 3 Protocol
3.4 IP address (2/2)
Every packet carries IP addresses of
the sender and receiver.
A router keeps a table of IP addresses of other computers
Chapter 3 Protocol
3.4.1 Global and Internal IP addresses (1/3)
Global IP address (also called registered IP address) is routable
understood by the routers on the Internet is precious resources
managed by ICANN (Internet Corporation for Assigned Names and Numbers).
Each network is assigned with only a few global IP addresses, used in mail server, Web server and routers etc.
As the Internet grows rapidly, global IP addresses will be used up finally.
Chapter 3 Protocol
3.4.1 Global and Internal IP addresses (2/3)
Local IP addresses (also called internal or private IP addresses) are not routable
cannot be used on the Internet identify computers within a network 10.x.x.x., 172.16.x.x., 192.168.x.x the choice is based on
the size of the network up to the discretion of the network adminstrator
The same internal IP address may be used by computers in other networks.
Chapter 3 Protocol
3.4.1 Global and Internal IP addresses (3/3)
Local IP addresses
Chapter 3 Protocol
3.4.2 IP Address and Port Number
Port number between 0 and 65,535 combines with IP address
The combination is called socket for bi-directional communication link between two programs
• of the Web server and Web browser so that received data will be directed to the correct program
Port numbers between 0 and 1,023 are reserved e.g. HTTP: 80, FTP: 21
Port numbers in the range 1,024 to 49,151 used by NAT to identify workstations in a LAN connected to the Internet
Chapter 3 Protocol
3.4.3 Conversion between Local and Global Addresses (1/2)
Network Address Translation (NAT) maintains an address translation table and
rewrites the IP address in the header of each incoming and outgoing packet.
3 main purposes: Translate between internal and global IP
addresses Enable computers to share global IP
addresses, using publicly available yet unused IP
address, or port numbers
Provide protection by hiding internal IP addresses
Chapter 3 Protocol
3.4.3 Conversion between Local and Global Addresses (2/2)
Chapter 3 Protocol
3.4.4 Assigning IP addresses
Two ways to assign IP address: manually assigning static addresses
to devices automatically assigning dynamic
address by Dynamic Host Configuration
Protocol (DHCP) Devices with static IP address:
servers network printers routers
Global IP addresses can be static or dynamic, depending on the ISP e.g. IP address for a home user is
dynamic by the DHCP of the ISP’s server
Chapter 3 Protocol
3.4.5 Problems with Global IP address IPv4 (IP version 4)
current addressing scheme uses 32-bit binary numbers run out soon due to rapid growth of the Internet
always-on Internet connections mobile wireless devices
• both require globally unique IP address
Chapter 3 Protocol
3.4.5 Problems with Global IP address
A. Current Solutions
The problem of scarcity of address in IPv4 solved by NAT
use port numbers to extend the global IP address
Chapter 3 Protocol
3.4.5 Problems with Global IP address
B. IPv6
IPv6 (IP version 6) in early stage of deployment uses 128 bits for each IP address e.g. 2031:32C5:130F:0:0:09C0:876A:130B allow up to 1015 endpoints in total
enough for individual computers and devices. built-in security -- IPSec
protect data by encryption mainly used in
mobile phones, high-end videoconferencing and privacy extension.
Chapter 3 Protocol
3.4.6 IP and MAC address (1/2)
MAC address IP addresses
permanent
burnt into NIC’s ROM
can be changed
logical
understood by NIC, bridge, switch
but not TCP, IP, NAT, routers
understood by TCP, IP, NAT, router
but not by NIC, bridge, switches
difficult to manage
changing a NIC means changing the MAC address
easier to manage
same IP address can be assigned to a computer after change the NIC
only provide information about manufacturer
provides more information
can tell whether the address is used internally or globally
cannot identify a network can identify a network
NetID can be worked out
Chapter 3 Protocol
3.4.6 IP and MAC address (2/2)
Chapter 3 Protocol
3.5 Subnetwork (1/3)
An IP address is logically divided into two parts: prefix NetID
identifies a network suffix HostID
identifies a computer on that network
Note: Subscribers of an ISP have the same NetID - explains why the location of anyone can be identified from the
global IP address
Chapter 3 Protocol
3.5 Subnetwork (2/3)
Why dividing an IP address? improves routing efficiency
reduces the size of routing tables in routers• by storing the NetID of major networks
– e.g. as the ISP’s network
allows network management easierby breaking a large network into smaller ones
• –known as SUBNETTING
• e.g. a school can be subnetted to networks
– for students, and
– for administration.
Chapter 3 Protocol
3.5 Subnetwork (3/3)
Chapter 3 Protocol
3.5.1 Notation and Size of Network (1/2)
CIDR (Classless Inter-Domain Routing) IP address/n, where n = bits for NetID
Ex.1
202.148.153.49/24
24 bits (3 bytes) for NetID HostID may vary from 0 to 255
but, 0 and 255 are reserved.
The maximum size of the network is 254 hosts
Chapter 3 Protocol
3.5.1 Notation and Size of Network (2/2)
Ex.2
128.10.0.0/16 16 bits (2 bytes) for NetID HostID may vary from 0 to 65,535
but, 0 and 65,535 are reserved.
The maximum size of the network is 65,534 hosts Ex.3
192.168.0.32/28 28 bits (3.5 bytes) for NetID HostID may vary from 0 to 15
but, 0 and 15 are reserved.
The maximum size of the network is 14 hosts
Chapter 3 Protocol
3.5.2 Subnet Mask
Subnet mask stored with each IP address specifies the boundary between NetID and HostID determines the maximum size of a network 32 bits long
1…..1 followed by 0 ….. 0
e.g. For 24-bit NetID, the subnet mask is
11111111 11111111 11111111 000000002
(255.255.255.010).
The amount of 0’s = number of bits for HostIDbut, HostID with all 0’s and all 1’s are reserved.
Chapter 3 Protocol
3.5.3 Special IP Address (1/3)
A. Network Address HostID with all 0’s
e.g. 128.10.0.0/16
denotes a network B. Broadcasting Address
HostID with all 1’s broadcasts a packet to all hosts on a network
called directed broadcastinge.g. 128.10.255.255/16 broadcasts to network 128.10.0.0.
Limited broadcasting:
255.255.255.255
used when a computer starts up
Chapter 3 Protocol
3.5.3 Special IP Address (2/3)
C. This Computer Address 0.0.0.0 used to identify a computer when it boots
for communicating with other computers
D. Loopback Address 127.x.x.x
e.g. 127.0.0.0 is called localhost used by programmers to test the communication capability
of a program no packets ever leave a computer
Chapter 3 Protocol
3.5.3 Special IP Address (3/3)
Chapter 3 Protocol
Classful Network (1/3)
The size of network is determined by the first four bits of an address not by the subnet mask Class A size = 224 - 2 = 16,777,214 hosts Class B size = 216 - 2 = 65,534 hosts Class C size = 28 - 2 = 254 hosts
Chapter 3 Protocol
Classful Network (2/3)
Chapter 3 Protocol
Classful Network (3/3)
used in specifying size of a LAN
