Algorithms and performance evaluation of the Xphone multimedia communication system

Abstract

We describe and evaluate the performance of 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 time-stamps 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.