Computer network

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introduction

• Number of computers (and usually terminals (point of connection)) interconnected by one or more transmission paths.

• Transmission path often is the telephone line due to its convenience and universal presence.

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network

• transfer and exchange of data between the computers and terminals.

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applications

• day-day transactions at department stores, banks, reservation counters, etc.

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advantages

• Sharing of resources.• Allows flexible working environment.– Employees can work at home by using terminals

tied through networks into the computer at the office.

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Computer network

• Collection of autonomous (acting independently) computers interconnected by a single terminology.

• Two computers are said to be interconnected if they are able to exchange information.

• Note:Neither the internet nor the world wide web (distributed system) is a computer network.

@prepared by S.Shrestha (comp 251)

@prepared by S.Shrestha (comp 251)

internet

• Internet is not a single network but a network of networks and the web is a single distributed system that runs on top of the internet.

• Internet stands for international networks.• Largest computer network system in the

world.• Global network of computers.

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@prepared by S.Shrestha (comp 251)

@prepared by S.Shrestha (comp 251)

History of internet?????

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Client server model

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Description

• One can imagine a company’s information system as consisting of one or more databases and some no of employees who need to access them remotely.

• In this model, the data are stored on powerful computers called servers.

• Servers: often these are centrally housed and maintained by a system administration.

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Contd…

• In contrast, the employees have simpler machines, called clients on their desks with which they access remote data.

• For example to include in spreadsheets (i.e. computer program allowing manipulation and flexible retrieval of especially tabulated numerical data).

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Working mechanism

• 2 processes are involved, one on the client machine and one on the server machine.

• Communication takes the form of the client process sending a message over the network to the server process.

• The client process, then waits for a reply meessage.

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Contd…

• When the server process gets the request, it performs the requested work or looks up the requested data and sends back a reply.

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@prepared by S.Shrestha (comp 251)

Network hardware

• 2 types of transmission terminology that are in wide spread use.

Broadcast linksPoint-point links

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1. Broadcast networks

• Single communication channel that is shared by all the machines on the network.

• Short messages (packets) sent by any machine are received by all the others.

• An address field within the packet specifies the intended recipient.

• Upon arriving a packet, a machine checks the address field.

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Contd…

• If the packet is intended for the receiving machine, that machine processes the packet.

intended for some other machine

Packet ignored

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broadcasting

• Addressing a packet to all destinations by using a special code in the address field.

• When a packet with this code is transmitted, it is received and processed by every machine on the network.

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multicasting

• Some broadcast systems also support transmission to a subset of the machines.

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2. point-to-point

• Consists of every connections between individual pairs of machines.

• To go from source-destination a packet on this type of network may have to first visit one or more intermediate machines.

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unicasting

• Point-point transmission with one sender and one receiver.

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internetwork

• Connection of two or more networks.• Example: internet.

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Wireless networks

• Divided into 3 main categories:– System interconnection– Wireless LANs– Wireless WANs

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System interconnection

– Short range wireless network.– System connection networks use master-

slave.– System unit (master), mouse-keyboard

(slave)• Master tells slave what address to use, when

they can broadcast , how long they can transmit, what frequencies they can use, and so on.

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Wireless LANs

• System in which every computer has a radio modem and antenna with which it can communicate with other systems.

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Wireless WANs

• Bluetooth– No cables– No driver installation

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Home networks

• Computers (desktop PC)• TV, DVD, VCR, etc.• Most homes already have networks installed

like:- electricity, telephone, cable TV, water, gas.

@prepared by S.Shrestha (comp 251)

@prepared by S.Shrestha (comp 251)