Floor control alternatives for distributed videoconferencing over IP networks

Applications that require the communication of multiple video streams can consume considerable bandwidth and computing resources, which poses a challenge for the widespread use of videoconferencing over the IP Internet. On the one hand, the bandwidth of the link connecting a given participant to a videoconferencing session may not be enough to support many video streams at bit rates of 500 kbps or more, especially when the participant is connecting to the rest of the Internet through a wireless link. On the other hand, the processing capacity of a participating site may not be enough to decode several video streams in real time. This paper explores the use of floor control over videoconferencing applications as a means to support videoconferences with many participating sites, but with a processing and communication overhead per site that is equivalent to a two-party videoconference. The main tradeoff we explore is the scalability attained with floor control versus the latencies incurred with floor transitions, which can be much too disruptive to the videoconference participants. We present a viable compromise in which only the video stream of the "floor holder" is sent to all sites, but the floor-passing protocol is such that it supports a brief overlap of the transmissions from the old and the new floor holder, such that the participants in the videoconference can instantaneously switch over to the media streams of the next speaker in an apparently seamless transition. Experimental results and implementation in a research video-conferencing system show that the proposed protocol can run effectively, eliminating race conditions, while maintaining scalability and reliability