Network Layer (Layer 3)
The primary responsibility of the network layer is routingproviding mechanisms by which data can be passed from one network system to another. It does not specify how the data is passed, but rather provides the mechanisms to do so. Functionality at the network layer is provided through protocols, which are software components.
Protocols at the network layer are also responsible for route selection, which refers to determining the best path for the data to take throughout the network. In contrast to the data-link layer, which uses MAC addresses to communicate on the LAN, network protocols use software configured addresses and special routing protocols to communicate on the network. The term packet is used to describe the logical grouping of data at the data-link layer.