1. 1 3 Computing System Fundamentals 3.4 Networked Computer Systems

2. 3.4.1 Network Topology

3. 3 Network: definition A way of connecting computers so they can: ‣ share software (programs and data), ‣ share hardware (expensive peripheral devices e.g. laser printers) and ‣ allow communication. The computers and peripherals on a network are collectively called nodes.

4. 4 LANs A Local Area Network (LAN) connects nodes over a single building or site. They tend to use electrical cable or short- range radio signals (wifi).

5. 5 WANs Wide Area Networks (WANs) operate over much larger distances than LAN’s. They tend to use other communications systems such as telephone lines, long-range radio signals (wi-max), microwave links and satellite links. The internet is a WAN.

6. 6 Network organisation Older LANs had a central mainframe computer and associated non-processing (dumb) terminals. Modern tendency in business is away from mainframes towards networked PC’s (workstations), which can also work as stand-alone machines, connecting to a PC working as a server.

7. 7 Network organisation The cost of a network is always greater than that of the individual computers. Networks may be peer-to-peer (all machines equal) or there may be one or several network servers, which control security and hold users' files and other resources. Such client/server networks are more common in business.

8. 8 Network topology The four main LAN topologies (shapes) are bus, ring, star and mesh. They may be connected to other networks via bridges or routers and a large network will probably be a hybrid type i.e. it will involve two or more of these topologies.

9. 9 Bus topology Cheapest since they use a common cable or backbone to which all devices are connected. The cable must be properly terminated so that signals are absorbed and don't bounce up and down the bus.

10. 10 Bus topology

11. 11 Bus topology Bus networks can be fragile - a bad connection or actual break can bring down most of the network. Bus networks can be slow when large data files are being transferred (they can only send one message at a time).

12. 12 Ring topology Nodes are connected in a ring (bus with the ends joined). More robust than a bus since data can go round either way. An electronic token can be used to regulate transmission (if a node has the token, it can receive/transmit, if it is finished it passes the token on).

13. 13 Ring topology

14. 14 Star topology Individual computers radiate out from the server or via a switch or hub. The cabling is more expensive, but wifi is now cheaper (wifi is always star). Vulnerable to a hub failure but if a cable breaks the other computers still operate.

15. 15 Star topology

16. 16 Hybrid topology

17. 17 Mesh topology Nodes to several or many of their nearest neighbours. Very reliable since data can be transmitted along any of several routes (the network can route around any failures). The internet is a mesh network.

18. 18 Mesh topology Node Node Node Node Node Node Node Node Node