On a shared medium, data link addresses are unique within the medium. In the enterprise, data link protocols provide functions such as finding a path and managing parallel paths.

The data-link and physical layers add new optional features. Elements in blue are required, those in green are unchanged from Ethernet, and those in beige are optional.

Network Layer: Handles routing of data packets across networks and includes protocols like IP. Transport Layer: Ensures reliable data transfer and includes protocols like TCP and UDP. Session Layer: ...

Networking author Howard C. Berkowitz begins a series on dealing with failures in specific layers and protocols.