The Network Layer

   Packets Across Networks

As we have just seen, a process in the Data Link Layer communicates with only one other peer process across a single communication link. However, a process in the Network Layer communicates with multiple peer processes across all communication links to which that node is attached.

The Network Layer accepts data passed down from the layer above (Transport Layer) and encapsulates it by adding a Network Layer header to the data. The header contains protocol information used by peer Network Layer processes as they forward the packet to its final destination. The Network Layer then passes the packet down to the layer below, the Data Link Layer. The Packets and Network Layer Diagram illustrates the relationship between these layers.