REACTIVE FLOW CONTROL FOR MULTIPOINT VIDEO SERVICES

摘要

The paper proposes a new service architecture and a new multipoint feedback mechanism for real-time multicast video. This mechanism solves the problem of the amount of feedback reduction, due to the increase of the number of destinations from the same source description by using a feedback pol ling mechanism and the problem of the available bandwidth variation by using a combination between the adaptive encoding and the feedback -based rate control. For the first mechanism, two algorithms are developed: one to locate the most congested branch In the multicast tree, the other to observe the overall congestion state of this tree. Another new procedure, based on in adjustment of the encoder's quantization parameter achieves the control of the total output rate from the video encoder. In addition, da ta partitioning is utilized to control the output rate of low and high priority information. The performances of the proposed feedback mechanism, associated with the encoding algorithm, were investigated on a series of simulations on a point -to-multipoint network model with seven ATM switches interconnected in a binary tree topology. The simulation results showed the scalability with the number of destinations of the cell rate and of the video signal quality and the impact of the propagation delay and of th e number of congested path, proving that video feedback mechanism provides better quality than a classical CBR service at the same amount of available bandwidth, and can adapt to varying degrees of congestion in the network in order to improve video quality.