3 Computing System Fundamentals
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Transcript of 3 Computing System Fundamentals
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3 Computing System Fundamentals
3.4 Networked Computer Systems
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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).