WRHMCC: a new congestion control mechanism for multicast applications

Congestion control for large multicast groups has been a challenging issue for widespread deployment of multicast services. Single-rate multicast congestion control schemes address both TCP-friendly and scalability issues with low complexity. However, they do not solve the well-known "drop-to-zero" problem, i.e., to prevent a slow receiver from slowing down faster receivers in the same multicast group. For this purpose, we propose a new single-rate multicast congestion control mechanism for heterogeneous receivers which helps each multicast receiver to receive at its desired rate. The basic idea is as follows. Each multicast receiver maintains and adjusts a window at itself just like what TCP source does. They calculate a desirable receive rate with this window and the RTT to the source and feed back this rate to the source and intermediate routers. The sender tunes its rate according to the fastest receiver in the group. Each multicast router does not copy each incoming multicast packet to all egress links in the multicast tree unconditionally but copy packet to egress links according to the rate information obtained from the downstream receivers. \´Good\´ egress links receive more packets while \´bad\´ egress links receive less packets. The proposed strategy is shown to be still TCP-friendly and scalable while eliminating the "drop-to-zero" problem.