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3 Computing System Fundamentals. 3.4 Networked Computer Systems. 3.4.2 Network Hardware. 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 ).
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3 Computing System Fundamentals • 3.4 Networked Computer Systems
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.
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.
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.
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.
Switch • A switch is similar to a hub but with some ability to filter out irrelevant traffic.
Bridge • A bridge links together LANs, letting through only the data destined for that LAN (thus reducing unnecessary traffic).
Gateway • A gateway is similar to a bridge, but can also translate data from one network protocol to another.
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.
Modem • A modem converts a computer’s digital data (stream of bits) to analogue (continuous wave) sound (DA conversion or DAC) and vice versa.
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).