What is Medium Access Control?

The basic MAC protocol for IEEE 802.11 is carrier sense multiple access with collision avoidance. In this case, the coordination decision is distributed over all the stations. In addition to this, the standard specifies a centralized MAC algorithm, called the point coordination function.

Which is built on top of the distributed algorithm? PCF provides contention-free service and is primarily intended for configurations in which a number of wireless stations are interconnected with each other and some sort of base station that attaches to a wired backbone. This is especially useful if some of the data is time sensitive or high priority.

Distributed Coordination Function:

1. CSMA/CA used for access control
2. when a collision is detected, a random back off timer is set
3. Positive acknowledgements are used.

Point Coordination Function:

1. built on top DCE, the point coordinator uses DCE to seize the medium
2. A point coordinator determines which station currently has the right to transmit by polling.