A hybrid adaptation protocol for TCP-friendly layered multicast and its optimal rate allocation

Layered transmission has been proposed as a solution to video multicast over the Internet. Existing protocols usually perform adaptation at the receiver and use static rate allocation techniques at the sender. As a result, significant mismatches between the fixed transmission rates and the heterogeneous and dynamic rate requirements for the receivers can occur. We show that such mismatches can be minimized by employing dynamic layer rate allocation at the sender by taking advantage of the recent development in layered video coding. Specifically, we study the optimization criteria for layer rate allocation, and propose a metric, called fairness index, which fairly reflects the degree of a receiver's satisfaction. We then formulate this into an optimization problem with the objective of maximizing the expected fairness index, and derive an efficient and scalable algorithm to solve it. We further demonstrate that such sender rate adaptation can be seamlessly integrated into an end-to-end adaptation protocol called HALM (hybrid adaptation layered multicast). This protocol is designed for the current best-effort Internet and is TCP-friendly. Its control overhead is also kept at a low level. Simulation results show that HALM improves the degree of fairness for receivers with heterogeneous bandwidth requirements, and interacts with TCP flows substantially better than static allocation based protocols. In addition, increasing the number of layers in HALM always leads to a higher degree of fairness and 3 to 5 layers are usually sufficient. However, this is not true for the static allocation based protocols.