The 802.11 MAC
O ne of the most important aspects of the 802.11 standard is the rules laid down for Media Access Control (MAC). Regardless of the physical layer 802.11 is implemented on (2.4-GHz ISM band, 5-GHz UNII band, and so on), the MAC rules stay the same. Distributed Coordination Function The 802.11 standard specifies two modes in which MAC can operate: contention free and contention based. In contention-based MAC, stations basically fight for access to the media. Similar to Ethernet, when a station wants to transmit first, it checks to see if another station is using the wire. In an Ethernet network, a station waits until the media is not in use and then transmits the packet. If another station transmits at the same time, it will detect the collision and randomly back off. This makes Ethernet a carrier sense multiple access/collision detection (CSMA/CD)–based algorithm.