Reliable multicast for ad hoc network with intermediate node support

Many applications of ad-hoc networks are based on the availability of a reliable multicast protocol. In this paper, we address the problem of reliability and propose a bandwidth-saved method to improve packet delivery of multicast protocol against failures caused by topology changes, congestion, air-interface interference and so on. Due to broadcast capacity, neighbors of multicast tree can help to store and re-transmit multicast data traffic. This protocol contains two parts. In the first part, a normal multicast protocol delivers data packet in group, while in the background, the intermediate nodes including multicast tree members and their neighbors selectively stores packets passing around them. In the second phase, a NACK-based re-transmission protocol tries to recover lost messages. This mecha-nism reduces the charge of source and congestion around source for re-transmission and saves bandwidth since some work is done by in-termediate nodes. Simulation results show that the packet delivery of multicast is significantly improved and in most cases, nearly one hundred percent delivery ratio can be got.