Overload Protection for IEEE 802.11 Cells

This paper presents a distributed admission control for the distributed coordination function of IEEE 802.11 wireless LANs that limits the risk of congestion collapse due to a high arrival rate of flows. This control scheme requires no modification to the current distributed coordination function; it works by performing a short, non-disturbing probe that estimates the MAC service time. The flow is admitted if the estimate is below a threshold. We show how the threshold may be adjusted dynamically to maintain an average packet loss rate below a configurable limit. We show via extensive simulations that the admission control avoids congestion due to flow arrivals and that it maintains the loss probability below the given threshold regardless of the offered load or number of stations. Our simulations also analyze the main drawback of our scheme: a reduction in the link utilization. The admission control efficiently protects cells from overload and it may offer soft QoS guarantees to multimedia flows without the need for scheduling or polling mechanisms in IEEE 802.11