Computer network mean a compilation of autonomous computers consistent by a single technology. Two computers are said to be organized if they are able to exchange information. The old model of a single computer helping all of the association computational needs has been replaced by one in which a large number of separate but organized computers do the trade. These systems are called computer networks.

Network topologies:
Network topology definite as the logical association of various processors in the network. The six essential complex topologies are as in bus, ring, star, tree, mesh and hybrid.

1. Bus Topology:
In bus topology all the computers are linked to a long cable entitle a bus. A node that needs to send data puts the data on the bus that carries it to the target node. In this topology any processor can information over the bus at any time. Since, the bus is shared in the middle of all the computers. When two or additional computers to send data at the similar time, an arbitration mechanism are needed to prevent simultaneous access to the bus.

A bus topology is easy to install but is not bendable such as it is difficult to add a new node to bus. In addition to this the bus stops functioning even if a bit of the bus smash down. It is also very difficult to separate blunder.

2. Ring Topology:
In ring topology, the computers are related in the form of a ring. Each node has accurately two nearby neighbours. To send data to a remote node on a ring it passes through many midway nodes to reach to its ultimate target.

A ring topology is as to install and reconfigure. In this topology, error isolation is easy because a signal that circulates all the time in a ring helps in identifying a faulty node. The data transmission takes place in only one direction. When a node fails in ring, it smashes down the whole ring. To overcome this drawback some ring topologies use dual rings. The topology is not practical to connect large number of computers.