What is network topology? Explain star and bus topology with its advantages
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Answer :
Topology of LANs
Networks can be laid out in different ways. The physical layout, or shape of network, or the way in which network connections are made is called a topology. It refers especially the locations of computers and how the cable is run between them. It is important to select the right topology for how the network will be used.
Bus topology In a bus topology the computers are connected in a line, the cable is just one or more wires; pass it along from computer to computer. It is a passive topology. When one computer sends a signal up (and down) the wire, all the computers on the network receive the information, but only one (the one with the address that matches the one encoded in the message) accepts the information. The rest disregard the message. Only one computer at a time can send a message; therefore, the number of computers attached to a bus network can significantly affect the speed of the network. A computer must wait until the bus is free before it can transmit.
The important issue in bus networks is termination. Since the bus is a passive topology, the electrical signal from a transmitting computer is free to travel the entire length of the cable. Without termination, when the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an un-terminated bus, it is called ringing. To stop the signals from ringing, you have to attach terminators at either end of the segment. The terminators absorb the electrical energy and stop the reflections. Cables cannot be left un-terminated in a bus network.
Advantages
Simple, easy to use, and suitable for very small networks
Least amount of cable is required to connect the computers together and therefore it is less expensive.
Easy to extend a bus, two cables can be joined with a BNC barrel connector, allowing more computers to join the network.
Star Topology
A star network is one in which all the cables run from the computers to a central location, where they are all connected by a device called a hub. Figure 2 shows a star topology. Each computer on a star network communicates with a central hub that resends the message either to all the computers (in a broadcast star network) or only to the destination computer (in a switched star network). The hub in a broadcast star network can be active or passive.
Figure 2: In a star topology the computers are all connected by Cables to a central point
Advantages
It is easy to modify and add new computers to a star network without disturbing the rest of the network.
Hub can accommodate multiple cable types.
Fault finding becomes very simple
Single computer failure does not bring down the whole network
It is more flexible among the remaining topology.