The network layer enables the transmission of variable-length packets from a source to a destination and performs routing over the network. The network layer functionality at the source includes accepting the packet from the layer above (transport layer and applications) and encapsulating it in a network level datagram that includes the source and destination addresses. Then, it delivers the packet to the data link layer so that it can be sent to the receiver. The destination node decapsulates the datagram, extracting the packet, that is delivered to the corresponding transport layer.