A network topology refers to the physical layout ofthe network in which all the devices are connected.The physical topology describes the actual layout ofthe network hardware. This includes all the hardwarethat makes up the network. The point of connectionto the network by the stations are called nodes orlink-stations. The goal of topology is to find themost economical and efficient way to connect all theusers to the network resources while providingadequate capacity to handle user reliability andminimize delay.

1.Linear Bus: This is the most popular

topology. Here a single main cable connectseach node, in what amounts to a single line ofcomputers accessing it from end to end. Eachnode is connected to two others, except themachines at either end of the cable, whichare connected only to one other. Informationframes originating at a station are propagatedaway from the station in both direction onthe bus. The network operating system keepstrack of unique electronic address for eachnode, and manages the flow of linear bustopology information based on thisaddressing scheme. If the destination fielddoes not matches the station address, thestation discards the information frame backon to the bus. And if the destination matchesthe station address, it accepts theinformation frame and process the frame

2. Ring topology:

This layout is similar to the linear bus,except that the nodes are connected in acircle using cable segments. In thislayout each node is physically connectedonly to two others. Each node passes theinformation along to the next, until itarrives at the intended destination.Performance can be faster on this systembecause each portion of the cablingsystem is handling only the data flowbetween two machines. This type oftopology can be found in peer-to –peernetworks, in which each machinemanages both information processingand the distribution of data files. Failureof a station in a ring topology disruptsthe ring because the information frameis not regenerated.

In this type of topology, a number of stationsare directly connected to a central station orcontroller. Communications on theconnecting inks between the stations arecentral station of a star topology can be bi-directional and are point-to point. A stationof this type of network passes informationframe to the central controller which thenforwards the information to the destinationstation. The central controller manages andcontrols all communications betweenstations on the network. This topology hasthe advantage of minimum data traffic alongthe cables(node to server only), for optimumperformance. But a single machine mustcoordinate all the data communication, thistopology requires an extremely powerful (and expensive) file server, plus additionalcable.

Tree topology arranges linksand nodes into distincthierarchies in order to allowgreater control and easiertrouble shooting. In order tofunction well networks usingtree topologies mustincorporate some form of‘traffic control’, to determinewhen traffic is allowed totravel up and down thebranches of the tree. The treetopology shields desperatenetwork groups affecting eachother.

In this topology each of thecomputer in the network isconnected to all thecomputers in the network.So in this topology if anyone computer fails then thenetwork is not down. But itis difficult to implementthis technology as thenumbering of computers inthe network increase.

Any network that incorporates elements of two ormore of the above discussed topologies is called as ahybrid network with a series of concentrators on thering can be called as a ring of stars.