Optimal branching factor for tree-based reliable multicast protocols

Abstract —In recent years, a number of reliable multicast protocols on transport layer have been proposed. Previous analysis and simulation studies gave evidence for the superiority of tree-based approaches in terms of throughput and bandwidth requirements. In many tree-based protocols, the nodes of the tree are formed of multicast group members. In this case, the branching factor, i.e. the maximum number of child nodes is adjustable. In this paper we analyze the influence of the branching factor on a protocol’s throughput and bandwidth consumption. This knowledge is important to configure protocols for best performance and to optimize the tree creation process. Our results show that the optimal branching factor depends mainly on the probability for receiving messages from other local groups. If local groups are assigned to a separate multicast address, the optimal branching factor is 2. On the other hand, if TTL scoping is used and therefore the probability for receiving messages from other local groups is greater than zero, larger local groups provide better performance.