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.