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). 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.

Coaxial cable

UTP cable

Fibre optic cable

Wifi base station

Microwave link

Satellite link

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).