Computer Network Collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users Computer network is an interconnected collection of autonomous computers. Two computers are said to be interconnected if they are able to exchange information through transmission media. Any type of data i.e. text, picture, audio and video can be transmitted by using network.

Advantages or Need Resource Sharing Simultaneous Access High Reliability due to alternative sources of data Reduced Costs Easier Backup Communication Medium Access to Remote Information Person -to- person Communication Interactive Entertainment

Network Topology Network topology is the physical interconnections of the elements (links, nodes, etc.) of a computer network The physical and logical topologies may or may not be identical in any particular network. The path taken by data from sender to receiver computer mainly depends upon the topology of the network.

Selection of a Topology Availability of physical communication line Reliability of the entire system Number of cables required Expandability of the system Transmission delays Maximum distance Maximum number of nodes Cost

Bus Topology A single cable acts as a backbone of the network and all the nodes or computers are attached to it by using T connectors . Each node on the network has a direct connection with the backbone cable. When one computer sends a signal up the cable, all nodes receive the information ,but the one with the address in the message, accepts the information while all other reject . Slow as the computer must wait until the bus is free. Requires a proper termination at both the ends of the cable.

Advantages and Disadvantages Less number of cable required. Easy to understand Nodes can be added without disturbing the rest of network Easy to understand and install If the communication lines fail, the entire system breaks down It is very difficult to repair the fault in this topology Heavy network traffic slows down the speed

Star Topology Each network host is connected to a central hub. Connects each node to the hub with a point-to-point connection. All traffic that transverses the network passes through the central hub. The hub acts as a signal booster or repeater. E.g. .Telephone Network

Advantages and Disadvantages Cheaper media of networking Less number of cables required Transmission delays do not increase by adding nodes If any node fails, the remaining portion of the network is unaffected Hub offers limited number of connections Hub represents a single point of failure. Cabling cost is more

Ring Topology Each computer is connected to the network in a closed loop or ring. Each machine or computer has a unique address that is used for identification purposes. The signal passes through each machine or computer connected to the ring in one direction. A token passing scheme is used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time.

Advantages and Disadvantages Shorter cable length required Delivers fast and efficient performance Suitable for high speed networks The failure of one machine will cause the entire network to fail. Addition of new node increases the communication delays Difficult to reach at the fault Difficult to add, remove or reconfigure the nodes in the network

Mesh Topology Each node is connected to more than one nodes of the system There exist multiple paths between two nodes In case of failure of one path, the other path can be followed Generally too costly and complex for practical networks, Used when there are only a small number of nodes to be interconnected