A Contention Window Based Differentiation Mechanism for providing QoS in Wireless LANs

Running real time applications over wireless LANs is becoming common place. These applications require QoS. But the most widely used wireless LAN, IEEE 802.11, does not have QoS support. Hence, providing QoS in 802.11 WLANs is an important issue due to its large installation base. In this paper, we propose a priority based service differentiation mechanism at the MAC layer. The MAC assigns different contention windows to two priority classes to provide service differentiation. The MAC protocol was designed such that minimal change is required in 802.11 firmware and yet the performance is comparable to 802.11e MAC. When collision occurs, contention window is increased in a linear fashion and the new contention windows for high and low priority traffic become non-contiguous. This unique method of contention window management provides better relative performance between the two classes. We also propose an enhancement to our base protocol that further increases throughput at light load condition. We present our simulation experiment results that show that our protocol has performance comparable to 802.11e.