Multicast Congestion Control Strategy based on Call Admission Control

Abstract

In most of multicast congestion control mechanisms, the sender of a multicast session will adapt its sending rate to satisfy the network congestion status and acceptable receiving rates of all receivers. However, most of these mechanisms suffer the “drop-to-zero” problem where the sender adapts its sending rate to the acceptable receiving rate of the slowest receiver in the multicast group. As the size of the multicast group grows, it is very likely that the slowest receiver will have a very poor network status, either highly congested or low bandwidth, which leads the throughput of the multicast group to almost zero. The essence of this problem is that, as network traffic varies from time to time, any receiver is very likely to suffer network congestion at some instance of time. When the network status is very bad, a receiver really should not deserve to receive normal service. In other words, receivers with normal network status should not be affected by receivers with poor network status. Therefore, in this paper, we advocate the integration of multicast congestion control mechanisms with a call admission control (CAC) scheme to avoid the “drop-to-zero” problem. The proposed mechanism uses a multicast congestion control algorithm to gather acceptable receiving rate of each receiver and adapt the sending rate of the sender to the slowest receiving rate. When there is a change of receiving rate or a join of new receiver, the CAC mechanism is used to determine whether to kick out receivers with slow receiving rate or a new comer with a slow receiving rate based on a reward function. Our simulation results show that the proposed CAC scheme can effectively drop slow receivers in multicast group and, thus, serve the majority of group receivers at a much higher throughput.