The network layer is responsible for routing, which is moving packets (the fundamental unit of data transport on modern computer networks) across the network using the most appropriate paths. It also addresses messages and translates logical addresses (i.e., IP addresses) into physical addresses (i.e., MAC addresses). This contrasts with the data link layer below it, which is responsible for the device-to-device delivery of packets using MAC addresses. Above the network layer is the transport layer, which is responsible for making certain that packets are delivered in sequence and without errors, loss or duplication.
