TOPOLOGIES OF LAN

The various rules/methods to connect the computers in a networking is known as Topology. In LAN various topologies exist:

Star Topology :-

Star Topology is forerunner of all other topologies. Here server acts as heart of LAN and all PCs are connected individually to it. It is the topology upon which telephone network is built. Every communication from every user's station goes through the central computer before reaching its destination. Central computer is very powerful and takes care of all networks responsibilities. The network is cheapest of all. To connect five systems, we just need four cables. But failure chances are more. If central computer fails whole network will go down. Sometimes star shaped LANs are built with duplicate central computers as it allows rapid recovery from failure. But this will add to cost of networking.

Merits:

Demerits:

1. Central computer must be very powerful.
2. Chances of failure are more.

•  Ring Topology :-

In Ring Topology each PC is connected to its neighboring PCs on either side. When all PCs and the server are similarly connected a ring is formed.

Ring Topology avoids dependence on central computer. Each node on ring can send a message to other terminal with a unique-address as Tag Sender that has a Tag & same is true for receiver. Receiver receives the message & sends an acknowledgement lo send Software for ring topology must contain tool to guard against messages with bad address.

Addition of a new station involves breaking the ring and adding on Ring-Interface Unit (RIU). Every Date Unit in ring contains source & destination address. Since ring is endless, data units will circulate continuously unless they are removed from ring. The sending station removes data unit after it has completed one round.

Merits:

1. It is a true distributed data processing system.
2. More reliable than STAR communication and is not dependent on HOST.

Demerits:

1. Addition of new Node increases delays.
2. complicated control software.

•  Bus Topology :-

All the PCs are connected to same cable in one stream. At one end is server and last terminal, at the other end is called terminator. As with ring structure, Bus Network has also a unique address. If geographic coverage needs to be expanded, repeaters which interconnect two buses are required.

In Bus Topology, least length of physical transmission medium is used. Coverage can be increased by extending the bus through use of repeaters. The Bus Topology is one of most popular in today's LAN marketplace. One reason for popularity is that its wiring requirement is comparatively simple and growth is obtained easily & quickly. With most bus structured networks. Workstations can fail or be added without disturbing the rest of network.

Merits:

Demerits:

1. Addition of new node increases delays.
2. Complicated control software.

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