A reliable subcasting protocol for wireless environments

This paper presents an end-to-end reliable multicast protocol for use in environments with wireless access. It divides a multicast tree into sub-trees where subcasting within these smaller regions is applied using a tree of retransmission servers (RSs). RM2 is receiver oriented [1] in that the transmitter does not need to know its receivers, hence offering better scalability. The Internet Group Management Protocol (IGMP) is used manage group membership whereas the IETF's Mobile IP offers support to user mobility and a care-of address (temporary IP address). Each RS has a retransmission subcast address shared by its members and which may be dynamically configured using IETF's MADCAP (Multicast Address Dynamic Client Allocation Protocol) [8]. Most importantly, RM2 uses a dynamic retransmission strategy to switch between multicast and unicast retransmission modes according to the extra load generated in the network as well as the wireless interfaces by packet retransmissions. It is shown through both analytical modeling and simulation that RM2's dynamic adaptation is not only important but necessary when considering mobile access.