Solutions to Performance Problems in VoIP over 802 . 11 Wireless LAN 1

VoIP over WLAN is poised to become an important Internet application. However, two major technical problems that stand in the way are 1) low VoIP capacity in WLAN; 2) unacceptable VoIP performance in the presence of coexisting traffic from other applications. With each VoIP stream typically requiring less than 10 Kbps, an 802.11b WLAN operated at 11 Mbps could in principle support more than 500 VoIP sessions. In actuality, no more than a few sessions can be supported due to various protocol overheads (For GSM 6.10, it is about 12). This paper proposes and investigates a scheme that can improve the VoIP capacity by close to 100% without changing the standard 802.11 CSMA/CA protocol. In addition, we show that VoIP delay and loss performance in WLAN can be compromised severely in the presence of coexisting TCP traffic, even when the number of VoIP sessions is limited to half its potential capacity. A touted advantage of VoIP over traditional telephony is that it enables the creation of novel applications that integrate voice with data. The inability of VoIP and TCP traffic to coexist harmoniously over the WLAN poses a severe challenge to this vision. Fortunately, the problem can be largely solved by simple solutions that require only changes to the MAC protocol at the Access Point. Specifically, in our proposed solutions, the MAC protocol at the wireless end stations needs not be modified, making the solutions more readily deployable over the existing network infrastructure.