Computer Network Compiled by: GF Kalumuna January 2015

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

Features of a Network Communication channel Hardware Software Network topology

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

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

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

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

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

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

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)

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

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)

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

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

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

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

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)