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

Today’s networks, including WLANs, transport different classes of services. A service differentiation is then essential to provide QoS. However, IEEE 802.11 for WLANs was primarily designed for best effort traffic and did not provide QoS specifications. IEEE 802.11e MAC has been then described to support QoS in WLAN. In this paper, we propose a new scheme for service differentiation which is based on the 802.11 standard and requires minor modifications. In fact, we act on DCF which uses 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 parameterizations of the geometric distribution which imply different dynamic differentiation modes and we provide an analytical study, using a Markov chain model, to compare our differentiation modes. We discuss our numerical results which give the performances evaluation of the proposed mechanism in term of throughput and delay.