Abstract: Until mechanisms for true real-time network communications are deployed and pervasive, one must rely on adaptive, best- effort congestion control methods to provide acceptable levels of service for interactive, real-time multimedia applications on the Internet. In this talk I report on our experiences with a novel best-effort media scaling congestion control scheme that was implemented in an experimental version of the Intel ProShare videoconferencing system, and tested over the Internet. The media scaling scheme is unique in that it employs two-dimensional media scaling -- media streams are independently scaled in bit-rate and packet-rate dimensions. The goal of our study was to (1) empirically assess the performance improvement of two-dimensional media scaling over the simpler, and more commonly employed, one- dimensional scaling approaches (e.g., bit-rate scaling) and (2) to determine if it was possible to sustain (adaptive) ProShare conferences for a significant enough fraction of the time that two-dimensional scaling could be considered effective.
With two-dimensional media scaling, we observed that high- quality ProShare conferences were sustainable nearly three times as often as with the unmodified system for conferences spanning up to 28 hops on the Internet. Moreover, when systems using one-dimensional and two-dimensional scaling were both able to sustain conferences, the two-dimensional scaling system always produced conferences with greater effective throughput and lower latency.
The study provides empirical evidence that two-dimensional media scaling can be used effectively to ameliorate the effects of congestion in the Internet and can significantly extend the usability of an interactive multimedia application on the Internet.