Distributed mechanisms for quality of service in wireless LANs

Wireless local area networks (WLAN) are gaining popularity at an unprecedented rate, at home, at work, and in public hot spot locations. As these networks become ubiquitous and an integral part of the infrastructure, they will be increasingly used for multi-media applications. There is limited Quality of Service (QoS) support in WLANs and this will become an impediment in deploying multi-media applications. In this paper, we present a tutorial on QoS support in IEEE 802.11 WLANs with a focus on the distributed MAC protocol of 802.11. Most QoS support mechanisms proposed for 802.11 use well known techniques such as priority assignment and fair scheduling and map QoS metrics into some existing 802.11 MAC parameter, thereby avoiding a redesign of the MAC protocol. We provide a taxonomy of the mechanisms and describe the essential concepts, problems, and advantages of each mechanism. From our study, we conclude that choosing the right set of MAC parameters and the QoS mechanism itself to provide predictable QoS in 802.11 networks is still an open problem.