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During recent years the IEEE 802.11 WLAN standard [1] has been widely deployed as the most preferred wireless access technology in office environments, in public hot-spots and in the homes. Due to the inherent capacity limitations of wireless technologies, the 802.11 WLAN easily becomes a bottleneck for communication. In these cases, the QoS features of the 802.11 e standard will be beneficial to prioritize for example voice and video traffic over more elastic data traffic.

The IEEE 802.11 medium access control (MAC) comprises the mandatory Distributed Coordination Function (DCF) as a contention-based access scheme, and the optional Point Coordination Function (PCF) as a centrally controlled polling scheme. However, PCF is hardly implemented in any products, and DCF represents the commonly used MAC mechanism of 802.11. DCF adopts carrier sense multiple access (“listen-before-talk”) with collision avoidance (CSMA/CA) and uses binary exponential backoff. A station not only goes into backoff upon collision. It also carries out a” post-backoff” after having transmitted a packet, to allow other stations to access the channel before it transmits the next packet.