1. Slide 1 What is a Computer Network? A computer network is a linked set of computer systems capable of sharing computer power and resources such as printers, large disk drives, CD-ROM and other databases. There are two types of network:  Local Area Network (LAN)  Wide Area Network (WAN)

2. Slide 2 Local Area Networks A local area network is a computer network across one building or site. Fileserver Printer Work Station Network Cable

3. Slide 3 Peer to Peer Network This describes a very simple network structure where shared resources such as printers are available but where there are very few other facilities. All computers on the network have similar specification and status.

4. Slide 4 Client-Server Network This method of network organisation requires one or more servers to which a number of clients may obtain services. The servers act as central resource managers for the network. A star topology is often used for this form of network.

5. Slide 5 Network Hardware Network hardware will include:  stations  servers file, print, web  passive components cables, connections, etc  active components repeaters, hubs, switches

6. Slide 6 Network Stations The network station (often called the client) will normally comprise:  PC  Network interface card (NIC). The NIC allows the computer to communicate with the network  Network Operating Systems eg. Windows 95/98, Windows NT, Appleshare, etc

7. Slide 7 Network Servers A network server is a computer which acts as a central storage point for files and applications. Servers also act as a connection point to shared peripherals such as printers.

8. Slide 8 Active Components Active components are required for all but the simplest of networks. These include:  repeaters  hubs  switches

9. Slide 9 Repeaters Due to loss of signal strength it is often necessary to use a repeater to boost the signal. A repeater is a hardware device to link together two cable segments. The repeater amplifies the signal it receives before passing it on.

10. Slide 10 Hubs A hub is a device which allows the interconnection of a group of users. A hub will forward any packet of data it receives over one port from one station to all of the remaining ports. Hubs are used in the star topology.

11. Slide 11 Switches A switch is “smarter” than a hub and offers more bandwidth. A switch forwards data packets only to the appropriate port for the intended recipient.The switch establishes a temporary connection between the source and the destination.

12. Slide 12 Routers A router receives packets of data transmitted over a network, and using their IP address, forwards them to the correct destinations over the most efficient available path.

13. Slide 13 Network Topologies The network topology is the theoretical arrangement of components on a network. There are four network topologies which you need to be aware of:  bus  star  Ring  mesh

14. Slide 14 Bus Topology Each device is connected to a main communications line called a bus.

15. Slide 15 Star Topology In the star topology all stations are connected to a central node, called a hub.

16. Slide 16 Ring Topology Each device is connected to a ring around which signals are sent. The devices are connected to the ring via spurs, or the connection may pass through the interface card

17. Slide 17 Mesh Topology A mesh network is the most expensive type of network to install

18. Slide 18 Protocols A protocol is a standard set of rules used to ensure the proper transfer of data between devices. In network design it is vital that a recognised protocol is used.

19. Slide 19 TCP/IP TCP/IP is a protocol which allows computer on different networks to communicate. TCP/IP is a pair of protocols  TCP - transmission control protocol  IP Internet Protocol

20. Slide 20 IP Addressing Every computer station on the internetwork must have an IP address. This IP address must be unique but is not encoded in the network interface. It is set by software in the computer.

21. Slide 21 Internetwork Hardware Connecting LANs together will require extra hardware:  bridges  routers  gateways

22. Slide 22 Bridges A bridge acts as a link between LANs. This will allow two LANs to appear to users as though they are a single LAN.

23. Slide 23 Routers A router is a device which receives data packets and sends them on via an appropriate route. It will have a number of network interface ports to allow connection to different segments to which data packets may be directed.

24. Slide 24 Gateways A gateway is a link between two dissimilar networks.. The communications between the networks are usually via public telecommunications networks. A gateway will normally be used to connect a LAN to the Internet.

25. Slide 25 Implications of Networks Computer networks have developed as a result of a perceived need and as a result of economic and technical factors. Computer networks have social, legal and ethical implications

26. Slide 26 Economic Factors The cost of communication technology  equipment costs are continually reducing and improving features mean that more is available for the same money. Access to expensive equipment  printers and mass storage are expensive so it makes sense to share them. Geographic spread of organsiations  video-conferencing and email, etc allow organisations to cope with geographic isolation.

27. Slide 27 Technical Factors Adoption of Internet technology  TCP/IP Adoption of International Standards  ISO OSI Development of Communication Technology  fast modems, ISDN, etc

28. Slide 28 Social Implications Individuals may become withdrawn from society Personal privacy may be compromised as a result of monitoring network use People may not have to move from rural communities to find Home working may allow strengthening of family life (?)

29. Slide 29 Ethical Implications Bogus doctors could easily offer medical advice over the Internet. Availability of unacceptable and inappropriate material within education Antisocial, criminal, racist or other prejudiced material may be distributed freely.

30. Slide 30 Legal Implications Copyright law  British law makes it illegal to copy someone elses copyright material. A lot of material on web pages is copyright Sometimes the breaking of this law is unwitting but in others it is deliberate (eg MP3 files of commercial recordings)