We know that inter networking is the process of connecting two or more networks together so that data transmission between networks may take place. There is possibility that the networks, which are to be connected, are not compatible. In such cases of incompatibility of networks, it is required that a "black box" be inserted at the junction point so that necessary conversions are possible as data packet moves from one network to the other. Such a black box in general is called 'relay'. Relays may connect to or more networks. Bridges and gateways are examples of relays used for this purpose.
BRIDGE
A bridge is a device to link two networks. A bridge is used to link same type of networks (LANs). When a packet (data packet) reaches the bridge, it decides whether it is to be addressed to a node on the other side of the bridge or on the same side. A bridge filters out those packets which are addressed to the same side of the network and passes all other packets which are addressed to some nodes on the other side of the network.
ROUTER
A router is similar in operation to a bridge, but it can connect two networks with different protocols. A router may be connecting two networks A and B. A message originating from node 3 of network A may be directed to node 5 of network B. The router checks the node address and the network address and use algorithms to find the best path to reach the destination. Different networks may use different protocols for communication. Therefore some kind of mutual understanding is required for compatibility between the two protocols so that data can be transferred from one network to any other. A router is the device which establishes understanding between the protocols of different networks.
GATEWAY
A gateway is used to connect two networks of different types, it is like a router in the sense that it finds the optimal path for a message directed to a specific node in a different network. In addition, it can convert the message from one code to another. For example, it can convert an e-mail message received in one format into another.
 |
| VARIOUS NETWORK CONNECTORS |
