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3 Computing System Fundamentals

3.4 Networked Computer Systems

3.4.2 Network Hardware

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The network interface

•Computers may be directly connected to a LAN, in which case they will need special hardware (the network interface card or NIC).

•Even if they only connect occasionally to a WAN (e.g. using a dial-up connection via a telephone line) they need a modem.

•Direct connections e.g. DSL are faster than dial-up connections.

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Connection media

•The medium of transmission may be:

‣ an electrical cable (e.g. coaxial or unshielded twisted pair - UTP),

‣fibre optic cable or

‣ via radio waves.

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Coaxial cable

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UTP cable

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Fibre optic cable

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Wifi base station

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Microwave link

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Satellite link

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Network hardware

•Various connection boxes co-ordinate the transmission of data with varying degrees of programability.

•Of those that follow, the important ones are:

‣hub,

‣ switch and

‣ router.

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Hub

•A hub is a junction box, acts as a repeater, amplifying and sending on signals to networked devices, but not discriminating on where they are for or from.

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Switch

•A switch is similar to a hub but with some ability to filter out irrelevant traffic.

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Bridge

•A bridge links together LANs, letting through only the data destined for that LAN (thus reducing unnecessary traffic).

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Gateway

•A gateway is similar to a bridge, but can also translate data from one network protocol to another.

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Router

•A router can translate and direct the traffic.

•They are used to manage internet traffic: data will always be passed on to a router nearer to their destination.

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Modem

•A modem converts a computer’s digital data (stream of bits) to analogue (continuous wave) sound (DA conversion or DAC) and vice versa.

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Modems

•Dial-up modem speed theoretically up to 56kbps (bps = bits per sec).

•ISDN (Integrates Services Digital Network), transfer rates of up to 144kbps).

•ADSL (Asynchronous Digital Subscriber Line), incoming rate ~8Mbps and outgoing ~1Mbps).