Journals Proceedings

Abstract

The most popular and widely used Wireless LAN standard all over the world today is IEEE 802.11. It is likely to play a major role in the next generation wireless communication networks. IEEE 802.11 WLANs has two basic co-ordination functions at MAC layer: DCF (Distributed Coordination function) and PCF (Point Coordination Function). DCF is the basic access function for asynchronous data services and is based on carrier sense multiple access with collision avoidance (CSMA/CA) with a binary slotted exponential contention (back off) algorithm .PCF uses a centralized polling method requiring a node to play the role of a point coordinator (PC) developed for time bounded services. Providing QoS support in IEEE 802.11 is challenging task, as QoS solutions for wired networks cannot be applied out-of-the-box for wireless mobile ad hoc networks, due to specifics of radio networking and mobility. QoS problem has two major perspectives: (1)network perspective (2) application/user perspective. Networks receive from the applications implicitly or explicitly their QoS parameters and need to respond to these requests by supplying QoS services. In this paper we first analyze the QoS limitations of legacy DCF and PCF IEEE 802.11 wireless MAC. Then, we present the upcoming IEEE 802.11e standard introduced as a proposal defining the mechanisms for WLANs aiming to provide QoS support to time-sensitive applications, such as, voice and video communications. Finally, we carry out a comparative study of legacy DCF and the IEEE 802.11e (EDCF), when supporting different services, such as voice, video, best-effort and background traffic.