Bus Topology :
Bus topology is multi-point data communication circuit. A single coaxial cable acts as backbone to link all the devices in the network. When one computer sends a signal up to the cable, all the computers on the network receive the information and where the address matches computer accept the information while all the others reject the information. Speed of bus topology is slow because only one computer can send a message at a time. A computer must wait until the bus is free before it can transmit. A heavy network traffic slows down the bus speed.
Bus topology requires proper termination at both ends of cable because adding and cancellation of waves results standing waves. The standing waves can distort the normal signal which are travelling along the cable. So terminators are attached at both ends of the cable terminators absorb the electric energy and stop reflection.
Bus topology is easy to understand, install and use for small networks. The cabling cost is less as the bus topology requires the least amount of cable to connect the computers. In the expansion of bus topology, repeaters can be used to boost the signal and increase the distance.
Ring Topology :
In a ring topology each node is connected to the next node, with the last one connected to the first. A ring topology is sometimes called a loop. Message flow around the ring is in one directional. There is no termination because there is no end to the ring. Each computer or device on the ring topology network acts as a repeater. It transmits data by passing a token around the network. If token is free computer waiting to send takes it, attaches the data and destination address and sends it. when token reaches its destination computer, data is removed. No one computer can monopolise the network because every computer is given equal access to the token. Failure of one computer on the ring can affect the whole network. Adding or removing the computer disturbs the network activity.
Star Topology :
In star topology all cables run from computer to central location where they are all connected by a device called hub. Signals from sending computers go to the hub and then transmitted to all the computers in broadcast star network or only the destination computer in switched star network. Since each workstation has separate connection to hub it is easy to troubleshoot. If the central hub fails, the whole network fails to operate. Here cabling cost is more. Many star network requires a device at a central point to rebroadcast or switch the network traffic.
Mesh Topology :
In mesh topology every device has a dedicated point to point link to every other device. Dedicated means that the link carries traffic only between two devices it connects. A fully connected mesh network has n(n-1)/2 physical channel to link n devices. Point to point links make fault diagnose easy. Mesh topology is robust because failure of single computer does not bring down the entire network. It provides security because every message sent travels along a dedicated line. Here cabling cost is more.
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