A Geometric Backoff Time Distribution of IEEE 802.11 DCF: An Analytical Study

Abstract

Today’s networks, including WLANs, transportdifferent classes of service. A service differentiation is thenessential to provide QoS. However, IEEE 802.11 for WLANs wasprimarily designed for best effort traffic and did not provide QoSspecifications. IEEE 802.11e MAC has been then described tosupport QoS in WLAN. In this paper, we propose a new schemefor service differentiation which is based on the 802.11 standardand requires minor modifications. In fact, we act on DCF whichuses the backoff procedure to solve contention in WLANs.For this scheme, we use, instead of the uniform distribution,a geometric distribution for random backoff time selection.Using a multi-class system, we propose three parametrizationsof the geometric distribution which imply different dynamicdifferentiation modes and we provide an analytical study, usinga Markov chain model, to compare our differentiation modes.We discuss our numerical results which give the performancesevaluation of the proposed mechanism in term of throughputand delay.