3 Computing System Fundamentals

1

3 Computing System Fundamentals

3.4 Networked Computer Systems

3.4.2 Network Hardware

3

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.

4

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.

5

Coaxial cable

6

UTP cable

7

Fibre optic cable

8

Wifi base station

9

Microwave link

10

Satellite link

11

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.

12

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.

13

Switch

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

14

Bridge

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

15

Gateway

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

16

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.

17

Modem

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

18

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).