Computer Network

1. Computer Network Compiled by GF Kalumuna January 2014

2. Computer Network • A way of connecting two or more computers together in order to gain access to different information or services

3. Features of a Network • Communication channel • Hardware • Software • Network topology

4. Communications Channel • Wires that connect the network • Node- a computer or hardware in a network • Why many communication channels? • Need for Bandwidth- capacity of a communication channel to carry information • Transmission speed

5. Communications Hardware • These are nodes • Examples of Nodes • Server – a computer that handles traffic and dispenses files/information (Cf Host) • Client- computer that uses services and information from the server • Bridge- connects similar networks together • Controller- Handles incoming dialup calls and forwards them

6. Multiplexer- splits a channel so that many nodes can use it • Router- Determines where to send or forward data on the network • Switch- selects the path for sending data

7. Communications Software The network operating system (NOS) • Helps to share different hardware (printers, applications and files) • Manages people on the network (cf security) The server software • Determines which computer can participate in the network • Ensures proper paths for communications to take place The client software • Helps to obtain information and use the services of servers

8. Network Topology • Also called configuration • The layout of computers and other devices and how they are connected • Bus Topology • Star Topology • Ring Topology • Hierarchical Topology

9. Bus Topology • Also called Ethernet • Each device handles its own communication control • No host computer • All communications travel along a common connecting cable, a bus. • As info passes, it is examined by each device if relevant for it • Ideal for few computers • Less expensive • Not as efficient as star network

11. Star Network • Several devices are linked to a central unit • The central unit may be a host computer or a file server • Each device asked “Polled” if it has a message to send, then allow to send it • Several users can share resources from the central computer • Ideal for linking several computers (organisation database)

13. Ring Network • Each device is connected to two other devices, hence, forming a ring • No central file server or computer • Messages pass around the ring until they reach the correct destination • Mainly used to link mainframes to cover a wide geographical area • Perform their own processing, but may rarely share with other mainframes • Ideal for decentralised organisations

15. Hierarchical Network Also called hybrid network Several computers are linked to a central host computer (cf star network) These other computers are also hosts to other computers or peripheral devices Levels/Hierarchy Mainframes (Top) Minicomputers (Sub) Microcomputers (Sub sub)

16. Allows various computers to share databases, processing power, & different output devices • Ideal in centralised organisations

18. Network Types • Three Important Types • Local Area Networks (LANs) • Metropolitan Area Networks (MANs) • Wide Area Networks (WANs)

19. Local Area Networks • Connects with computers and peripheral devices in close physical proximity • Linked by cable e.g. telephone • Often use a bus design • Users can share equipment (e.g printer, file server) • Other equipment can be added to the LAN e.g mini/mainframe computers, optical storage devices • It can be linked to another LAN

21. Metropolitan Area Networks • Link between office buildings in a city • Covers a larger area than LAN • Used by many individuals and organisations • They use wires/cables • Can extend up to 50 kms

23. Wide Area Networks • Countrywide and worldwide networks • Use microwave relays and satellites to reach users over long distances • The widest WAN is the Internet (entire globe)