Improving end-to-end multicast rate control in wireless networks

In this paper, we focus on an equation based single rate TCP-Friendly Multicast Congestion Control (TFMCC) protocol, primarily proposed for wired networks. In TFMCC, the rate is determined as a function of packet loss ratio (PLR), round trip time (RTT) and packet size, where each receiver estimates its throughput at each RTT, using an equation that estimates the steady-state throughput of a TCP source. The multicast source adjusts its rate according to the slowest receiver (a.k.a. Current Limiting Receiver CLR), within the session. However, when this approach is applied in wireless networks, mobility related packet losses will cause frequent changes of the congestion representative. In this paper, we evaluate TFMCC in a wireless environment, while using an equation that models the steady state throughput of a multicast source controlled according to the AIMD (Additive Increase Multiplicative Decrease) approach. Another modification consists of monitoring RTT variations at the source side in order to predict any modifications at the CLR in relation to the network conditions. The source adjusts the sending rate according to the new selected CLR. Simulation results show that these modifications result in remarkable performance improvements with respect to throughput (increase by as much as 50%), time to react (reduction by as much as 25%), and magnitude of oscillations at the wireless nodes, without carrying any changes at the MAC layer.