COMPUTER NETWORK

UNIT 1

IntroductionProf. Chintan Patelchintan.patel@marwadieducation.edu.inMEFGI , Rajkot

COMPUTER NETWORK

TEACHING SCHEME

Theory : 4 lecture / weekPractical : 1 lab / week

Evaluation Scheme

University exam (theory) : 70Mid sem exam (theory) : 30Internal : 50

Books

1 Computer network, by Tanenbaum , Pearson.2 Introduction to data communication and

networking by Forouzan,TMH.

Syllabus

• Introduction :

• The Physical Layer :

• The data link layer

• The medium access control sublayer

• The network layer

• The transport layer

• The application layer

Introduction

• Use of computer network• Network hardware• Network software• OSI Model(Open system interconnect)• TCP/IP Model• Comparison • The internet• X.25 Frame relay • ATM(Asynchronus transfer mode)• ETHERNET• WIRELESS LAN : 802.11

Computer NetworkNetworking is the linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software.

Use of computer network

• Business Application• Home application• Mobile usage• Social issues

Business Application

• Resource sharing Make all programs , equipments , and specially data available

to anyone on the network without regards to the physical location of the resource and user.

• Client server modal• Communication medium• E commerce

Client – server model

Small network with 2 clients and one server

Client : Simple user computer in networkServer : Powerful Computer on which data is storedRequest : Message send by client to serverReply : Reply by server to client based on request

Client – server model

Communication medium

• Email • E commerce

Home applications• Access to remote information• Person to person communication• Interactive entertainment• Electronic commerce

Difference between Client-server model and person to person communication

In person to person communication , There is no fix client and server.

Best example : Watsapp , Wechat for mobile and yahoo group chat or google group chat, mobile conference

Network Hardware

• Broadcasting• Multicasting• Point to point network

• Local Area Network• Metropolitan Area network• Wide area network

Local Area Network

• Within single building or campus• Used to connect personal computer and work

stations.• Traditional LAN runs at 10 mbps to 100 mbps.• Broad cast LAN.

Ring and Bus

Metropolitan Area Network

• Communication Subnet• Transmission Lines• Switching element(Routers)

Wide area network

• Covers city….• Cable television network

• Relation between hosts on LANs and the subnet.

• A stream of packets from sender to receiver.

Wireless Networks• System interconnecting.

Wireless components of computer, Keyboard , mouse Connect using bluetooth

• Wireless LANs. IEEE 802.11 Standard

• Wireless WANs.

• (a) Bluetooth configuration• (b) Wireless LAN

Network software

• Protocol Hierarchy• Design issues of layer• Connection-oriented and Connection

less services

Protocol hierarchy

• Layers, protocols, and interfaces.

• Physical medium• Interface• Header• Design Issues

Error Control Flow control Routing Multiplexing and De multiplexing

Connection Oriented and Connection less service

• Connection oriented service• After telephone system

Establish a connection Use the connection Releases the connection

• Connection less service• After postal system

Message have full destination address Routed through system and reached to destination

• Quality of service Reliable service (no packet loss)

With acknowledgement

• Request reply service used in client server model

• Service : Set of operations that a layer provides to the layer above it. What operations to be performed.

• Protocol : Set of rules governing the formats and meaning of packet or messages.

• GOOGLE FIBER.• GOOGLE BALLON

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REFERENCE MODELS• The OSI Reference Model

• The TCP/IP Reference Model

• A comparison of the OSI And TCP/IP

Reference model

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• OSI Model is very important as well as protocol discussed are also very important.

• TCP / IP model it self is not much of use but protocols inside are very important.

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The OSI Reference model• Proposed by ISO(International Standard Organization).• Called As ISO OSI Reference model. (Open System Inter connections).• Why open system inter connection?• Open system is a set of protocols that allows any two different system to

communicate regardless of their underlying architecture.• Purpose of OSI Model is to show how to facilitate communication

between different system without changing in their underling hardware.

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Principles applied to layers

• Where different abstraction is needed• Each layer should perform well defined

functions.• Must follow internationally standardized

protocol.• Information flow should be minimum.

EACH LAYER HAS SEPARATE INTERNATIONAL STANDARD

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Peer-to-peer process• Layer x on one machine directly communicate with Layer X on

another m/c with some series of rules called protocols.

The physical Layer• Transmitting raw bits over communication channel.• Representation of Bits.• Defines transmission mode : • Defines encoding(0 and 1 changed in signal)• Defines the types of transmission mediums• Defines topology configuration.• Decides data rate.• Purely hardware layer.

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Data link layer• Converts physical layer data into error free data for network layer• framing• Transmit the frames.• Physical addressing (provide sender and receiver mac address in header)• Traffic regulation mechanism• Flow control• Error control• MAC Sub layer : To control access to the shared channel .

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Hop to Hop delivery

To send data from A to F, First Data link layer at A will send data to the Data link layer B.GATE: Data link layer is responsible for Hop to Hop delivery.

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The Network Layer• Responsible for the delivery of individual packet from one host to another host• Routing : (How packets are routed from source to destination).• Logical Addressing.• Congestion control.• Quality of service provided(Delay, transit time , Jitter).• Solves problems like:

Address used by 2nd network may be different by 1st

Packet may be too large. Protocol may differ.

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Source to Destination delivery

• GATE : Network layer is responsible for End to End or Source to Destination delivery.

Router makes the decision based on destination.

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The Transport Layer• Segmentation and Reassembly• Service point Addressing

Delivery should not be from one computer to the next but it should also be from specific running process on computer to specific running process on another.

Adds service point address or Port number• End to End Error control and flow control.• GATE : Error correction is usually achieved through Retransmission.• GATE: Responsible for Process to Process delivery

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The Session layer• Allow user on different machine to establish session between them.• Dialog Control(Keeping track of whose turn is to transmit).• Token management(Preventing two parties from the attempting same critical operations

at same time).• Synchronization (Check pointing long transmissions to allow them to continue from

where they were after crash ). If system is sending file of 2000 pages. its advisable to insert check point after every

100 pages. In this case if crash happens at 523 page no. than retransmission of 501 to 523.not

previous pages.

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The presentation layer• Concerned with syntax and semantics of the information

transformed.• Translation : Presentation layer at sender changes the

information from sender dependent format to common format. Presentation layer at receiver dos vice versa.

• Encoding• Encryption• Compression

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• Providing services to users.• Widely used application protocols like HTTP.• File transfer protocol , SMTP Protocol.• Allows user to access files in remote host , to retrieve files

from a remote computer for use in local computer.

The Application layer

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GATE• Layer responsible for dialog control – Session layer.• Suppose in packet loss , system is retransmitting only loss packets .

which layer is responsible : Session layer. Which activity : Synchronization or check point.

• Which layer of OSI Provides privacy : Presentation layer by encryption.

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TCP/IP Reference model

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The Internet Layer• IP(Internetworking protocol)

Unreliable and connection less protocol – A best effort delivery. No error checking. No guarantee of receiving .

• GATE: IP transforms packet in datagram format.• Data gram can travel along different route and can arrive out of sequence.• ICMP(internet control message protocol)

To send notification of datagram to sender. sends query and error reporting messages.

• IGMP(Internet group message protocol)• ARP(Address resolution protocol) : Associating logical address with physical

address. Used to find physical address when logical address is known

• RARP(Reverse ARP) : provides IP address when physical address is known.

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The Transport Layer

• Responsible for delivery of message from one running process to another process.

• Similar to OSI Model.• End-to-End transport layer protocols.

TCP (Transmission control protocol) UDP (User datagram protocol) SCTP (Stream control transmission protocol)

Combines best features of TCP And UDP

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TCP And UDP

• TCP : Reliable connection oriented protocol• Allows byte streaming originating at one m/c to be delivered without

error on any other m/c in internet.• Divides a stream of data into smaller units called segment.• GATE : In Transport layer data will be in which formats : segments• Segments have sequence number for reordering .• TCP collects data grams from IP and reorders them based on

sequence number.• Receiver will reassemble the received message.• Also handles flow control.

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UDP(User Datagram Protocol)

• unreliable• Process to process protocol • Adds port address , checksum error control and

length information.

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The Application Layer

• Contains all higher level protocols.• TELNET(Provides bidirectional text oriented

communication).• FTP• SMTP• DNS (domain name system)• HTTP

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Comparison of OSI And TCP / IP• Central concept in OSI are

Services Interface Protocol

• TCP/IP Model did not clearly distinguish between above 3.• OSI Model was devised before the corresponding protocol were invented.• TCP/ IP , protocol was came first and model is just description of existing

protocols.• OSI model has 7 layers and the TCP/IP has 4 layer.• OSI Model supports connectionless and connection oriented communication in network layer and only connection oriented communication in transport

layer.• TCP/IP model has only connection less in network layer but supports both in

transport layer.

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Some Important Devices

• WORK STATION• HUB• SWITCH• BRIDGE• ROUTER• GATEWAY

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CONNECTION ORIENTED NETWORKS

History• Comes from world of telephone companies.• All packet will follow same route.• So if line will down , call is aborted.• Why telephone companies like it??

1. Quality of service Once connection is established , less chance of packet loss

because resources are reserved for that connection. 2. Billing

Clock can be easily maintained . so billing can easily done.

Connection Oriented Networks• X.25

Establish a connection with remote computer. That is placed a telephone call.

Data packet was consisting of 3 byte header and 128 byte of data. Header consisting of Connection number, A packet sequence number , An

acknowledgement number.

• Frame Relay

Connection oriented network with no error control and no flow control. In order delivery , No error control , No flow control. Most important application is interconnecting LAN at multiple company

offices.

• ATM (Asynchronous Transfer Mode)

ATM

• Asynchronous transfer mode.• Connection oriented.• Solved many communication problem by

merging voice , data , cable TV , smoke signals.• ATM was more success full than OSI and now

widely used in telephone systems.

ATM Virtual circuit• Virtual circuit is connection.• Permanent virtual circuit is permanent

connection between two hosts.• First sending a packet for to set up connection.• Router will make entry in its internal table.

• After establishing the connection , send a data.• Here data will be small , fixed size packets called

a cells. Total 53 byte = 5 byte header + 48 byte data.

• Connection identifier is there in header based on that router can tell which cell belong to which connection.

• Helps router in routing decisions

• Fixed length packet can be sended at high speed but variable length can not.

• All cells follows the same route to destination.• Cell delivery is not guarantee but order is.• During talk, problem can not occur in telephone.• ATM N/W’s are organized like WAN , With lines

and router.• Most common speeds for ATM n/w are 155

mbps.

ATM Reference model• Different than OSI and TCP/IP.

• 3 LAYERS. The physical layer. ATM ATM Adaption layer.

• Physical layer will deals with physical medium• ATM Layer deals with cells and cell transport.

Defines layout of cell and tells about header fields. Deals with establishment and release of virtual circuit. Congestion controls.

• ATM Adaption layer(AAL). Deal with packet segmentation and reassembly.

• User plane : Deals with data transport, flow control , error control.

• Control plane : Deals with connection management.

• Plane and layer management deals with resource management and interlayer coordination.

• Physical layer = Transmission convergence(TC) + PMD(Physical medium dependent)

• Transmission Convergence sub layer : converts bits (0 and 1s ) in cells.

• PMD : Handle bit timing.

Ethernet

• Architecture of the original Ethernet.

Wireless LANs

• (a) Wireless networking with a base station.• (b) Ad hoc networking.

Wireless LANs (2)

• The range of a single radio may not cover the entire system.

Figure (a)The hidden station problem. (b) The exposed station problem.

The Hidden Terminal Problem• Wireless stations have transmission ranges

and not all stations are within radio range of each other.

• Simple CSMA will not work!• C transmits to B.• If A “senses” the channel, it will not hear C’s

transmission and falsely conclude that A can begin a transmission to B.

The Exposed Station Problem

• The inverse problem.• B wants to send to C and listens to the

channel.• When B hears A’s transmission, B falsely

assumes that it cannot send to C.

Wireless LANs (3)

• A multi cell 802.11 network.