Virtual PCF: Improving VoIP over WLAN performance with legacy clients
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Date
2009-07-22T15:37:28Z
Authors
Ismail, Usman
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Abstract
Voice 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 on
WLANs is data traffic but as more people use wireless networks as their primary
access 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, bursty
traffic and perform poorly for VoIP streams. Experimental and analytical results
have shown that a single 802.11b access point operating at the maximum 11 Mbps
rate 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 Coordination
Function (DCF) used by 802.11 MAC layer. The problem can be addressed by using the optional Point Coordination Function (PCF). However PCF is not widely
implemented in commodity hardware nor likely to be. There is a similar problem
with the proposed 802.11e standard for quality of service. To solve these problems
we propose Virtual PCF, a legacy-client compatible solution to increase the number
of simultaneous VoIP calls. We implement Virtual PCF, a scheme which employs
a 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 of
supported VoIP sessions.
Description
Keywords
VoIP, WLAN