Current schemes for multicast packet video cope with congestion by adapting the transmission rate of a variable rate codec at the source. We propose a new approach, based on receiver- rather than source-adaptation, where a video source is encoded hierarchically with each layer of hierarchy distributed on a separate network channel. Each receiver can then dynamically adapt to local network capacity by adjusting the number of layers it receives. In order to deploy such a system, we must at the same time develop a layered codec tailored for this model. We present a prototype coder that has been designed specifically for our receiver-based congestion avoidance scheme. In order to evaluate the efficacy of our approach, we have implemented it in an existing Internet remote conferencing application and constrained the complexity of our design to run in real-time on standard workstations. Even with this constraint, our codec can generate a flexible range of layers while exhibiting reasonable compression performance.
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