Mr Satyendra Mohan Srivastava JIT Barabanki

COMPUTER NETWORKS

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COMPUTER NETWORKS

1/4/2017

A network is a collection of device referred to as nodes connected via media links

A node may be a computer, joysticks, printer and other devices generated by other nodes on the network

The various links connecting the devices are known as communication channels

The main purpose of a communication system is the exchange of data or information between two parties or points

TransmitterTransmission

systemSource Receiver Destination

Source System Destination System

BASIC COMMUNICATION MODEL

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PSTNServerModemModem

Public Telephone NetworkWorkstation

ESTABLISMENT OF COMMUNICATION

BASIC COMMUNICATION MODEL

The terminology communication refers to information or data transfer mechanism via telegraphy, telephony, television and other modes

The generated information or data transfer mechanism must follow the agreement between the two parties

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COMPUTER NETWORK CRITERIA

A network must meet certain criteria. Few of them are:

Performance

a) Transit time (Time elapsed between two devices)b) Response time (Time elapsed between enquiry and response)

Reliability

Security

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OSI MODEL

1/4/2017

International Organization of standardization (ISO) ensure the nationwide and world wide data communication

The various standards can be accumulated into a framework. The framework designed and developed by the ISO is known as Model for Open System Interconnection (OSI)

It is usually known as OSI reference model

It is also known as ISO-OSI model due to its ability to deal with other system

The term open refers to the systems which are open for interconnection with the other systems

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OSI MODEL

1/4/2017

Layer 7 Application layer

Layer 6 Presentation Layer

Layer 5 Session Layer

Layer 4 Transport Layer

Layer 3 Network Layer

Layer 2 Data Link Layer

Layer 1 Physical Layer

Layer 0 Transmission media

User

A seven layer ISO-OSI reference model

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OSI MODEL

1/4/2017

Router Router Host A Host B

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

PhysicalPhysical Physical

Physical Physical

Physical Physical

Application protocol

Presentation protocol

Session protocol

Transport protocol

Respective layer host router protocol

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OSI MODEL

1/4/2017

All the application may or may not use all the seven layers

The lowest three layers are mostly used by all applications

Each layer must handle the message or data above or below it

Each layer must process the data to the next layer

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AN EXCHANGE USING OSI MODEL

1/4/2017

7

6

5

4

3

2

1

7

6

5

4

3

2

1

Transmission Medium

T2 T2

1110010101010101010101

H6

L7 data

L7 data

L6 data H5

L5 data H4

L4 data H3

L3 data H2

H6

L7 data

L7 data

L6 data H5

L5 data H4

L4 data H3

L3 data H2

1110010101010101010101

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PHYSICAL LAYER

1/4/2017

101010100101

L2 data

Physical layer

Physical layer

101010100101

L2 data

From data link layer To data link layer

Transmission Medium

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PHYSICAL LAYER

1/4/2017

The physical layer allows the transfer of data from one computer to another

The bits on the physical layer is only concerned with reception and transmission of signals

The electrical and physical signals are usually represented by either 1 or 0

It defines the type of encoding, transmission rate (the no. of bits transmitted per second) and synchronization of transmitter and receiver

It determine the type of topologies, network connection type (point to point connection or multipoint connection), bandwidth and multiplexing among devices

It also determines the characteristics and transmission mode between two devices

The various connecting device associated at the physical layer are hubs, couplers, cables, connectors, repeater, receivers, transmitters and multiplexers

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DATA LINK LAYER

1/4/2017

From network layer

Data link layer

L3 data

L3 data T2 H2

10101100011101

Frame Frame

L3 data

L3 data T2 H2

10101100011101

Data link layer

To network layer

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DATA LINK LAYER

1/4/2017

Data link layer is responsible for node to node delivery of the data

The reliability of data packet is major focus point

The various data from network layer in the form of packets are transform into frames

The various frames at the Data link layer is provided to the physical layer

Frames are usually manageable data units received from network layer

It add header with the frame to define the address of the receiver or the physical address of the sender

It provide the mechanism for flow, error and access control

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NETWORK LAYER

1/4/2017

From Transport layer

Network layer

L4 data

L4 data H3 Packet

L3 data

To data link layer

From Transport layer

Network layer

L4 data

L4 data H3 Packet

L3 data

To data link layer

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NETWORK LAYER

1/4/2017

The function of network layer is ensure the delivery of packets from source node to the destination node across networks

Network layer doesn’t play an important role when the system are connected via the same links

The network layer transform the logical network address into the physical machine address

It also provide the priorities and routes to the messages

It is mainly focused on the circuits or packet switching (messages)

It mainly provide the various communication services like network layer error control, flow control and packet sequence control

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TRANSPORT LAYER

1/4/2017

From session layer

To network layer

L4 data

Transport layer

L5 data

H4 H4 H4

Packets

L4 data

L4 data From network layer

L4 data

Transport layer

L5 data

H4 H4 H4

Packets

L4 data

L4 data

To session layer

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TRANSPORT LAYER

1/4/2017

Transport layer ensures the arrival of intact and in order messages

It also ensure the error and flow control from source to the destination level

It provide the mechanism for division of messages into the packets

The header of transport layer include the services of addressing of different processes to the destination

End to end flow control is provided rather than a single link

It ensure the error free intact and in order arrival of message

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SESSION LAYER

1/4/2017

From presentation layer

To transport layer

L6 data

H5

Sessionlayer

synsynsyn

L5 data

To presentation layer

From transport layer

L6 data

H5

Sessionlayer

synsynsyn

L5 data

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SESSION LAYER

1/4/2017

The Session layer ensure the synchronization, establishment and maintenance of communication system

It allows an interaction session(dialogue) between the two systems

It provide the mechanism for check points(synchronization of points)

In the transmission during the crash, it ensures the transmission of data from that point irrespective of the retransmission of data from the start

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PRESENTATION LAYER

1/4/2017

L7 data

L7 data

Decode, encrypted and compressed data

H6

Presentation layer

L7 data

L7 data

Decode, encrypted and compressed data

H6

Presentation layer

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PRESENTATION LAYER

1/4/2017

The layer ensure the syntax and semantics of the information exchanged over the communication link

It ensures the format of data(translation of data into desired form) for the user and the system

It provide the mechanism for decryption at the receiver end and encryption at the transmitter end

Data compression and other mechanism can be implemented to reduce the bandwidth requirement of the data

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APPLICATION LAYER

1/4/2017

User

L7 data

FTAM

Application layer

User

L7 data

FTAM

Application layer

To presentation layer From presentation layer

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APPLICATION LAYER

1/4/2017

It is the upper or top layer in the OSI model

It endure the mechanism(services) to support the various user application such as e-mail, file transfer and database

The application layer provides a software emulation of a terminal at the host node located remotely across the geographical data

The user node communicate software terminal and via software terminal user node can communicate to the host terminal and vice versa

The software provide the elusion that the remote host can communicate to its own terminal

It ensure the mechanism of file access, management and its transfer

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TCP/IP REFERENCE MODEL

1/4/2017

OSI Model TCP/IP model

Application Application

Presentation

Session

Transport Transport

Network Internet

Data Link Host-to-network

Physical

These two layers are not present in this model

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NETWORK TOPOLOGY

1/4/2017

Network Topology

MeshTopology

StarTopology

BusTopology

RingTopology

TreeTopology

The topology of a network refers to geometric representation of the relationship existing between all the links via connecting devices or nodes

The various geometrical representation can be classified as follow :

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BUS TOPOLOGY

1/4/2017

Dropline

Dropline

Dropline

Dropline

Tap Tap TapTapCable end Cable end

The bus topology is a multipoint data communication circuit

The bus is a passive topology due to absence of electronics to amplify the signal

When the signal sends on the cable, all computer on the network receive the information i.e. information is broadcasted

One with the address matches the packet information, it receives the informations and other neglects it

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RING TOPOLOGY

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Ring TopologyRepeater

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STAR TOPOLOGY

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Hub

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MESH TOPOLOGY

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TREE TOPOLOGY

1/4/2017

HubHub

HUB

Hub

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LOCAL ACCESS NETWORKS

1/4/2017

Modem

Modem

Access links

Edge router

(a) Local network

(b) Company networkEnd systems

Edge router

Access links

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PHYSICAL LAYER TRANSMISSION MEDIUM

1/4/2017

The terminology medium represent the messages transmitted in the some space or in a communication channel

The different media show different properties and can be used in a different environment

The main function of physical layer is to provide mechanism for the transportation of stream of data from one device to another

We categorizes the transmission media as wireless or wired media, guided and unguided media and so on

A basic classification of transmission medium is shown on the next slide

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CLASSIFICATION OF TRANSMISSION MEDIUM

1/4/2017

Transmission Media

Guided or wired media

Unguided or wireless media

Twisted pair cable

Co-axial cable

Fibre-optic cable

Microwave links

Infrared

Air acts as medium

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SWITCHING METHODS

1/4/2017

Packet Switching

Switching

Message Switching

Circuit Switching

Switching methods provide the information regarding the connections and data flow in the network

Data is send via the public switch telephone network

Switching mechanism allows data to traverse between different routes

Switching can be mainly divided into following categories:

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ISDN

1/4/2017

ISDN stands for Integrated Services Digital Network (ISDN)

ISDN is a WAN (Wide Area Network)

ISDN can be understand as a resultant of the computer and communication technologies

A narrow band ISDN is the first generation of ISDN

The first generation of ISDN provide 64 kbps of user channel as the basic mode of switching with the circuit switching orientation

Frame relay is the important narrow band device in the first generation

The broadband ISDN is the second generation ISDN

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ISDN

1/4/2017

The advantage of broadband ISDN is its higher data rate, mainly in Mbps

ISDN is based on the standard define by the ITU – T

It provide the services over the wide range of application

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