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The prevalence of the IEEE 802.11b technology leads to the emergence of Wi-Fi based AV conferencing applications. However, due to the "best-effort" transport service and other unpredictable factors such as user mobility, location and background traffic, the transport channel behavior often fluctuates drastically. It thus becomes rather difficult to configure an appropriate de-jitter buffer to maintain the temporal fidelity of the AV presentation. We propose in this paper an adaptive delay and synchronization control scheme for AV conferencing applications over campus-wide WLANs. Making use of a distributed timing mechanism, the scheme monitors the synchronization errors and estimates the delay jitters among adjacent MDUs in real-time. It piece-wisely controls the equalization delay to compensate for the delay jitters experienced by MDUs in a closed-loop manner. We investigate the performance of the proposed scheme through trace-driven simulations. Simulation results show that the scheme is capable of dynamically balancing between synchronization requirements and latency requirements in all scenarios. In particular, compared with solutions using a static setting, the proposed scheme is able to achieve a gain of around 100 ms in end-to-end delay with the same amount of MDU losses under some media-unfriendly situations.
Date of Conference: 18-20 Oct. 2004