Congestion control for multipoint videoconferencing

Abstract

Multipoint videoconference service allows multiple and far-away conferees to conduct a meeting without leaving their offices. Variable-bit-rate video compression is attractive for videoconferencing, because it can provide a constant image quality and it can effectively utilize the communication bandwidth via statistical multiplexing. When some conferences temporarily generate heavy traffic to a link, congestion occurs and some video packets have to be discarded. Since the packets of different conferences are multicast to different number of conferees, the loss of different packet will affect different number of people. If we discard the packets sent to the smallest number of conferees, we can minimize the number of affected conferees to give the best mean quality of service, but the conference having a smaller number of conferees will suffer from a poorer quality of service. Therefore, we must consider both the mean quality of service and fairness in congestion control. We propose a congestion-control strategy for multipoint videoconferencing. This strategy has a control parameter which we can tune to make a tradeoff between the mean quality of service and fairness. In addition, the strategy only involves some simple arithmetic and logic operations, and hence, it can be executed quickly for real-time congestion control.