Static subgroup-based source recovery for reliable multicast in reliable networks

In this paper, we consider the problem of multicasting large files over a reliable network. In a reliable network, errors are transient and any change in the multicast tree is a rare occurrence. Further, the loss of a packet is correlated in the sense that a packet lost at a link will result in a loss to all downstream recipients. We propose to partition the recipients into static subgroups during the construction of the multicast tree. Whenever a NACK is received, the source retransmits the packet to all members of the subgroup from which the NACK came. This recovery method eliminates the overhead of joining/leaving subgroups associated with dynamic recovery schemes. This scheme reduces the NACK implosion by allowing all NACK from a subgroup to be merged in one NACK. We proposed an objective function to judge the merits of static subgroup-based recovery schemes. Further, we proved that computing the optimal subgroups is NP-hard. We provide an heuristic for computing subgroups with low cost of recovery and study its performance by simulation.