Admission control for variable bit rate traffic using variable service interval in IEEE 802.11e WLANs

Abstract

The IEEE 802.11 working group is currently working on the standard IEEE 802.11e and introduces the hybrid coordination function (HCF) to provide better QoS support to real-time traffic. A reference design of simple scheduling and admission control algorithm is proposed in a TGe consensus proposal. However, this scheduling and admission control unit only consider the mean data rate and mean packet size. The rate and packet size variation are not taken into account. Thus, it is only efficient to CBR traffic and the packet loss rate of VBR traffic may be very high. In W. F. Fan et al. (Aug. 2004), we analyzed the packet loss rate of the reference scheme and proposed a new method to determine the effective TXOP duration for admission control so that the packet loss rate of VBR flows can be guaranteed. In both reference and our proposed scheme, all stations use fixed schedule service interval (SI) which is the minimum of all maximum service interval of all admitted flows. Thus, maximum packet delay of all stations is limited by the most stringent SI and some traffic with larger delay bound may be over-guaranteed. Also, the efficiency of the admission control scheme in W. F. Fan et al. (Aug. 2004), becomes lower than that of the reference one. In this paper, we extend our admission control scheme by using variable service interval to improve the efficiency about 20% - 30% and avoid over guarantee on packet delay. Also, the packet loss rate of VBR traffic can be guaranteed