This layer controls the operation of the subnet,how packets are routed from source to destination.
If too many packets are present, such congestion is controlled by network layer.
n/w layer allows heterogeneous n/ws to be interconnected.
The basic function of the transport layer is to accept data from above,split it up into smaller units if need be,pass these to n/w layer and ensure that pieces all arrive correctly at the other end.
The transport layer is a true end-to-end layer,air the way from source to destination.
The difference between layer1 through 3,which are chained and layers4 through 7,which are end-to-end.
To be continued..