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RoutersRepeatersBridgesHubSwitchesGateways

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FillersServersModemsNetwork CardsCables

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You will all have come across the term 'Computer Networks' many times. The chances are you know all about LANs and WANs, network topologies, Intranets and Internet.

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A Router is a device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route.

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• Reads the data packet's destination address• Looks up all the paths it has available to get to that address.•• Checks on how busy each path is at the

moment•• Sends the packet along the least congested

(fastest) path.

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• ill signals fade as they travel from one place to another.

• Each type of network cable has a maximum useable length. If you go beyond that length, the signal will be too weak to be useful.

• Of course, computers on a real network can easily be more than 200 meters apart. Therefore the network cable is split up into segments. Each segment is less than the maximum length allowed. Joining the segments together is a device known as a 'Repeater'.

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• A Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network

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• There are many network topologies available:• Star - uses a hub• Tree - uses a hub• Bus - does not use a hub• Ring - does not use a hub• To allow the Star and Tree network topologies to work

properly, each computer must be able to send data packets to any other computer on the network.

• The network 'Hub' allows computers to share data packets within a network.

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• Each computer will be connected to a single 'port' on the hub. So if you purchase an '8 port hub', you will be able to connect up to eight computers together.

• You can also 'daisy chain' hubs to allow even more computers to join the network.

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• A network cable can only have one data packet in it at any instant.

• So if two or more computers want to place a data packet on to the network at exactly the same time, then a 'data collision' will take place.

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• A gateway converts the data passing between dissimilar networks so that each side can communicate with each other. i.e. converts data into the correct network protocol.

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• Just like Gateways, a Filter can be a mix of hardware and software components.

• A filter can also prevent data packets from leaving the company network. For example, a rule could be set up that only allows an authorized server within the network to send data outside the local network.

• A filter is an essential component of a 'Firewall'.

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• In some small networks, every machine is equally likely to have a resource that another machine needs to use.

• For example a small home network may be set up like this:

• There are files stored on each computer. One machine is linked to the scanner, whilst another is linked to a printer. The game machine is linked to the internet, which all three machines can use.

• This is fine for small networks as the number of requests to use a resource is not going to be too high.

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• A server is any machine that provides a service for other users on the network.

Common services include:• Email server• Internet Proxy server• Intranet server.

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• Some trivia: 'Modem' is a made-up word.• Originally engineers called it the 'MODulation -

DEModulation' box. But it was such a mouthful that naturally they ended up calling it the MODEM.

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• Standard modems come in two forms. An external box that links to your computer either through a serial or USB port, or an internal modem that is plugged directly to the motherboard inside the computer.

Wi-Fi modems• In addition to telephone modems, radio has now

become very popular as a means of connecting to the internet. The device that allows you to do this is called the Wi-Fi modem

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• Network cards are required in every machine connected to the network. They allow the signal from the network to be transmitted to the machine – this could be via a fixed cable, infra red or radio waves.

A network card that uses a standard cable network socket.

A Wi-Fi network card with an external aerial for the signal. Vishesh Kumar

How do you transfer data from one point to another on a network?This has to be done by some physical effect.There are three main methods of transferring data:•Electrical•Radio or Microwave•Infrared

•Electrical:•A multi-wired cable with a socket at each end is used to connect the various devices together e.g. computer to hub, hub to switch or switch to router etc.

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Radio or MicrowaveMicrowaves are just a small part of the radio spectrum, but because they are so widely used, they tend to be called by their own name.

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Infra-RedThis is a very familiar method of transferring data if you are at all aware of your remote control ! The television remote control makes use of an infra-red link.PDA and personal organisers often make use of an infra-red link to synchronise calendars and 'to-do' lists.

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Vishesh Kumar MCA -5th Sem.