Computer network @prepared by S.Shrestha (comp 251)
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Transcript of Computer network @prepared by S.Shrestha (comp 251)
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Computer network
@prepared by S.Shrestha (comp 251)
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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.
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@prepared by S.Shrestha (comp 251)
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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)
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@prepared by S.Shrestha (comp 251)
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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)
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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.
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@prepared by S.Shrestha (comp 251)