Network Laye
The network layer provides communication between the multiple networks. Whereas the data link layer provides the communication between two systems on the same network of two systems are connected to the same link there is usually more need for a network layer. However if the systems are attached to the different networks ( links) with connecting devices there is often a need for the network layer to accomplish sources to destination delivery. It defines addressing and routing ( logical link) between sources and destination. This layer also makes sure that data packets are transmitted across the networks correctly.Other responsibilities of the network layer include the followings.
- Logical addressing. The physical addressing implemented by the data link layer handles the addressing problems locally. If a packet passes the network boundary we need another addressing systems to help distinguish the source and destination systems. A header to the packet coming from the upper layer the among other things includes the logical addresses of the sender and receiver.
- Routing. When independent networks or links are connected to create internet works of a large network the connecting devices ( called routers or switches) route or switch the packets to their final destination. One of the functions of the networks layer is to provide this mechanism.