Supporting VBR VoIP Traffic in IEEE 802.11 WLAN in PCF Mode

With fast deployment of wireless local area networks (WLANs), the ability of WLAN to support real time services with stringent quality of service (QoS) requirements is attracting ever-increasing research interest. In this paper, we evaluate the capability of the point coordination function (PCF), which is part of the medium access control (MAC) mechanisms specified in the IEEE 802.11 standard for WLANs to support voice over IP (VoIP) applications. The capability of PCF mode in support of variable bit rate (VBR) VoIP traffic is investigated, where the silence suppression technique is employed in voice codecs so that no packets are generated in silence period. The impact of voice traffic burstiness and load on the average end to end delay is also evaluated, and various voice models are used to compare the results. Our simulation shows that under the PCF mode the end to end delay of VoIP traffic may be effectively reduced by using VBR mode for the VoIP traffic. Moreover, the end to end delay is not sensitive to the burstiness of the voice traffic. These features make the PCF channel access method a promising alternative for conveying VoIP traffic in present IEEE 802.11 WLANs.