Virtual PCF: Improving VoIP over WLAN performance with legacy clients

VoIP;WLAN;Computer Science

Ismail, Usman

University of Waterloo

关键词: VoIP;    WLAN;    Computer Science;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/4510/1/paper_uw-ethesis.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

AbstractVoice over IP (VoIP) is one of the fastest growing applications on the Internet.Concurrently, 802.11 Wireless LANs (WLANs) have become ubiquitous in residential, enterprise, campus and public networks. Currently the majority of traffic onWLANs is data traffic but as more people use wireless networks as their primaryaccess medium, a greater portion of traffic will be real-time traffic such as VoIP traffic. Unfortunately 802.11 networks are designed to handle delay-insensitive, burstytraffic and perform poorly for VoIP streams. Experimental and analytical resultshave shown that a single 802.11b access point operating at the maximum 11 Mbpsrate can support only 5 to 10 VoIP connections simultaneously. Intuitively, an 11 Mbps link should support approximately 85 bi-directional 64Kbps (G.711) streams.The reason for this under-utilization lies primarily in the Distributed CoordinationFunction (DCF) used by 802.11 MAC layer. The problem can be addressed by using the optional Point Coordination Function (PCF). However PCF is not widelyimplemented in commodity hardware nor likely to be. There is a similar problemwith the proposed 802.11e standard for quality of service. To solve these problemswe propose Virtual PCF, a legacy-client compatible solution to increase the numberof simultaneous VoIP calls. We implement Virtual PCF, a scheme which employsa variety of techniques to improve both uplink and downlink VoIP QoS. This alleviates delays and packet loss due to DCF contention and doubles the number ofsupported VoIP sessions.