Study on nominee selection for multicast congestion control

Nominee selection plays a key role in nominee-based congestion control, which is essential for multicast services to ensure fairness and congestion avoidance. Without valid design of nominee selection mechanism, the design of congestion control protocols could be inefficient or even flawed. Existing nominee selection schemes choose nominees by comparing the calculated throughput of receivers using the TCP throughput equation with the measured loss rate and round-trip time. Since the calculated throughput varies with different transmission rates, it may not accurately indicate the eligibility of a receiver to be the nominee. This causes the problem that a new nominee is not necessarily ‘worse’ than the current one and the ‘worst’ receiver could not be selected accurately. In this paper, we study the nominee selection principles and mechanisms. First, we address the problem in existing schemes by identifying the conditions for the valid use of calculated throughput. Next, we propose a new general nominee selection algorithm (GNSA) as a solution and prove that GNSA converges to the ‘worst’ receiver and the expected number of iterations is less than (1+ln n), where n is the group size. Finally, we demonstrate through ns-2 simulations the benefits of GNSA in terms of better fairness properties and less iterations to converge than existing nominee selection schemes such as that in TFMCC.