Back Pressure Based Multicast Scheduling for Fair Bandwidth Allocation

Saswati Sarkar, Leandros Tassiulas

Abstract: We study fair allocation of resources in multicast networks with multirate capabilities. In multirate transmission, the session source hierarchically encodes its signal and the receivers subscribe to the appropriate number of layers. The objective of the network is to distribute the layers fairly. This can be attained either by computing the fair rates first, and then using a scheduling policy to attain the fair rates, or by using a scheduling policy which allocates the fair rates without computing them explicitly. The first requires knowledge of system parameters like link bandwidth, which are not generally known to the link schedulers. The second approach is more realistic. We present a scheduling policy which allocates the fair rates without computing them beforehand. We have presented analytical and experimental results demonstrating the fairness of the resulting rate allocation. In addition to guaranteeing the fair rates, this policy confines the packet losses to enhancement layers, and protects the more important base layers, when there is shortage of bandwidth. Furthermore, this policy does not require any knowledge of traffic statistics, is computationally simple, and is essentially local information based.