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Algorithms and performance evaluation of the Xphone multimedia communication system

We describe and evaluate the performanceof the algorithms used in Columbia University’s “Xphone” multimedia communication system. The system assumes a “best-effort” operating system and network, and provides synchronized video/audio acquisition/playback (locally or across a network) with minimized and bounded end-to-end delay. Synchronization is achieved using an algorithm based on timestamps and device state information. The effects of jitter (delay variation) are mitigated using silence detection; the end-to-end delay is kept bounded using a restart mechanism. Finally, for live video sources, we describe a source bit-rate adaptation algorithm that maximizes the video image quality to the available network bandwidth and video display window size. Keywords—Multimedia communication systems, media synchronization, source rate control, application development systems.