Supporting VoIP Services in IEEE 802.11e WLANs

Voice over Internet Protocol (VoIP) over Wireless Local Area Network (WLAN) is becoming popular thanks to its cost efficiency. However, it has been a challenge to provide good quality of VoIP services in WLANs, which is due mainly to (i) the nature of contention-based channel access of WLAN Medium Access Control (MAC); (ii) the presence of coexisting non-real-time data traffic; and (iii) the time-varying WLAN capacity caused by transmission rate diversity and variation of stations over time. In this paper, we propose a simple, effective and viable solution to improve the quality of VoIP services in 802.11e contention-based WLANs, which basically utilizes the advanced features of 802.11e MAC for QoS support. The key ingredients of our solution include (i) a priority queue to serve the VoIP traffic with higher priority than the non-realtime data traffic; and (ii) a conservative history-based admission control scheme for VoIP services, which accommodates the transmission rate diversity and variation of ongoing VoIP sessions over time. Simulation results demonstrate that our solution admits as many VoIP calls as possible without compromising the quality of their services.