A dual-track approach to TCP-friendly reliable multicast

TCP-friendly reliable multicast protocol refers to multicast protocol that can have quick responses to network congestion and allows fair sharing of bandwidth with existing unicast TCP flows. In the window-based congestion control method, adjustment of the sending window and packet recovery are two inter-related issues. When packet loss occurs at any one receiver, the sender's window is reduced by half and it cannot move forward until the given receiver acknowledges the receipt of the repair packet. As a result, the throughput of the mutlicast session can be unacceptably low when the size of the mutlicast group is increased. In this paper we propose a dual-track approach that can significantly improve the overall throughput. The sender maintains two sending tracks, namely the fast track and the slow track. The fast track tries to deliver packets to receivers at a higher pace whenever possible. Packet losses on the fast track are recovered via the slow track. By doing so, packet recovery is decoupled from the rate control so that unnecessary delay in the fast track can be avoided. It has been shown that the dual-track approach is TCP-friendly and can significantly improve the throughput of the mutlicast session.