4. IEEE 802.11e extension for quality of service

The 802.11e QoS amendment was approved in July 2005. Based on IEEE 802.11, it defines several mechanisms to facilitate the use of multimedia applications on wireless LANs. In particular, for each class of traffic defined by IEEE 802.1p, this amendment defines a set of access rules adapted to the medium.

• These rules are implemented by two new coordination functions.

  • The first, centralized one, is called HCF (Hybrid Coordination Function). The corresponding medium access policy, HCCA (HCF Controlled Channel Access), is equivalent to PCF, but gives more control to the access point, particularly when it comes to interrupting a contention period.

  • The second distributed method is called EDCF (Enhanced Distributed Coordination Function). The corresponding medium access...