Achieving optimal performance by using the IEEE 802.11 MAC protocol with service differentiation enhancements

Wireless local area networks are currently evolving to support adequate degrees of service differentiation. Work is in progress to define an enhanced version of the IEEE 802.11 distributed coordination function, which is capable of supporting quality of service for multimedia traffic at the medium access control layer. In this paper, we aim at gaining insight into one mechanism to differentiate among traffic categories, i.e., differentiating the minimum contention window sizes according to the priority of different traffic categories. The contribution of this paper is the analysis of the optimal operation point where maximum throughput can be achieved. Through the analysis, we answer some fundamental questions about the existence and uniqueness of the optimal operation point, about the maximum system throughput, about the existence of simple rules to decide if the system operates under the optimal state or not, and about procedures to lead the system to the optimal operation point. The other contribution is the proposal of a simple adaptive scheme that makes the system operate under the optimal operation point and, at the same time, achieve target service differentiation between different traffic flows. The results that are obtained in this paper are relevant to both theoretical research and implementations of real systems.