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Transcript
3 Computing System Fundamentals 3.4 Networked Computer Systems 1 3.4.1 Network Topology Network: definition • A way of connecting computers so they can: ‣ ‣ share software (programs and data), ‣ allow communication. share hardware (expensive peripheral devices e.g. laser printers) and • The computers and peripherals on a network are collectively called nodes. 3 LANs • A Local Area Network (LAN) connects nodes over a single building or site. • They tend to use electrical cable or shortrange radio signals (wifi). 4 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. 5 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. 6 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. 7 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. 8 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. 9 Bus topology 10 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). 11 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). 12 Ring topology 13 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. 14 Star topology 15 Hybrid topology 16 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. 17 Mesh topology Node Node Node Node Node Node Node Node 18 Node