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In recent years, many 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 small. 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.
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