High Capacity VoIP Services in 802.11 Networks

IEEE 802.11 employs distributed coordination function (DCF) channel access mechanism which is based on carrier sense multiple access with collision avoidance (CSMA/CA). This standard was primarily designed to support best-effort traffic. Moreover, due to the contention-based approach, the bandwidth utilization is inherently inefficient. Therefore, the number of voice over IP (VoIP) calls which can be supported is severely limited. For example, the G.711 speech codec supports only 8 calls in an 802.11b network. We present a new method to increase VoIP capacity in Wi-Fi networks. This methodology requires no change to the existing DCF. It relies on contention-free channel access to improve the efficiency of bandwidth utilization without requiring the support of standard-based point co-ordination function (PCF). The access point (AP) uses packet aggregation in the downlink and scheduling in the uplink to enhance the throughput. Through mathematical analysis, we find that the proposed mechanism results in about 300% improvement over the baseline model. Using this, the G.711 codec supports 27 calls in 802.11b network