Hello Friends, In this blog post I am going to let you know about the network layer need, why do we need network layer while establishing the communication over the network.
The network layer is responsible for routing a packet within the subnet, that is from the source to the destination nodes across multiple nodes in the same network, or across multiple networks.
This layer ensures the successful delivery of a packet to the destination node. To perform this, it has to choose a route. A route could be chosen before sending all the packets belonging to the same message(virtual circuit) or it could be chosen for each packet at each node(datagram).
This layer is also responsible for tackling the congestion problem at a node when there are too many packets stored at a node to be forwarded to the next node. Where there is only one small network based on broadcast philosophy(e.g. a single ethernet LAN), this layer is either absent or has very minimal functionality.
There are many private and or public subnet operators who provide the hardware links and the software consisting of physical, data link, and network layers(X.25).
They guarantee error-free delivery of a packet to the destination at a charge. This layer has to carry out the accounting function to facilitate this billing based on how many packets are routed.
When packets are sent across national boundaries, the rates may change, thus making this accounting function complex. A router can connect two networks with different protocols, packet lengths, and formats.
The network layer is responsible for the creation of a homogenous network by helping to overcome these problems. At this layer, a header is added to a packet, which includes the source and destination addresses(logical addresses).
These are not the same as the physical addresses between each pair of adjacent nodes at the data link layer. If we want to send a packet from A to D(Fig1), addresses of nodes A and D ( i,e ADDL(A) and ADDL(D)) are these logical addresses…
Which are added to the actual data to form a data unit at the network layer(Dn). These addresses, and in fact the whole of Dn remains unchanged throughout the journey of the packet from A to F to G to D.
Only the physical addresses of the adjacent nodes keep getting added and removed, as the packet travels from A to F to G To D. Finally, at node D, after verifying the addresses, ADDL(A) and ADDL(D) is removed and the actual data is recovered and sent to the transport layer at node D, as shown in fig2(a,b).
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