Medium access control

All practical communications devices share a medium, even a point-to-point connection, and medium access control (MAC) techniques are the means by which sharing is possible. Applications include local area networks both wired and wireless, longer-ranged wireless networks such as cellular telephony and military tactical radio communications, and long-haul resources such as satellites and optical networks. It is not limited to data networks.

In the Open Systems Interconnection Reference Model, medium access control is at the data link layer, but there are many communications systems in which the medium access has to be arbitrated at the physical layer.

Methods include reservation, contention, and token-based. A reservation method reserves some resource, such as a time slot relative to the start of a cycle of communications, a frequency within a shared part of the electromagnetic spectrum, or a physical connection within an interconnection fabric.