The capacity of VoIP over 802.11

As Voice over IP (VoIP) technology becomes a reality, service providers will be able to offer enhanced VoIP applications not presently possible with circuit-switched type networks. Combining new applications and services with the IP Multimedia Subsystem (IMS) network will increase revenue potential. The combination of wireless local area network (WLAN) technology with VoIP and IMS features could become an attractive solution for enterprise voice infrastructure. Service providers can quickly enable enterprise Voice over WLAN (VoWLAN) services, which does not require any investment in re-wiring the premise. In this paper, we introduce the VoIP architecture over WLAN, and study, through both queuing analysis and simulations, the limiting capacity of such systems when operating in the distributed coordination function (DCF) or enhanced distributed channel access function (EDCAF) mode as defined in the IEEE 802.11b/802.11e standards. Our major conclusions are that: 1) packet aggregation and using short preambles can significantly increase VoIP capacity; 2) request to send (RTS)/clear to send (CTS) message exchange does not benefit VoIP; 3) In order to support simultaneous data and voice traffic on the same carrier, it is necessary to employ EDCAF as defined in 802.11e. © 2007 Alcatel-Lucent.