A NAK Suppression Scheme for Group Communications Considering the Spatial Locality of Packet Losses

Today's extensive use of multicast communication demands efficiency, scalability, and reliability. Numerous schemes have been proposed to improve these critical areas and some progress has been realized. Among the most recent and effective schemes that address this issue include the tree-based NAK suppression scheme that emphasizes on reducing NAK implosion at the repair node. The procedure employed would be an optimal solution, if in fact, for every multicast session transmission, at least one receiver node is guaranteed to receive the packet. However, the largest portion of packet loss in multicasting is due to buffer overflow and as a result there is significant spatial locality of packet losses among nodes of a local group. We propose a NAK suppression scheme that considers this property. Compared to the existing schemes, the proposed scheme will significantly reduce traffic congestion, NAK implosion at repair nodes, and the overall error recovery delay. While the issue of traffic congestion reduction is obvious when receiver nodes do not have to make unfruitful attempts to acquire retransmissions from other local group members that are already starved of the same packets, the much reduced NAK implosion at repair nodes and error recovery delay are clearly illustrated in our simulation results.