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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
CHINTAN PATEL(ASSISTANT PROFESSOR)
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.