Dynamic retransmission control for reliable mobile multicast

Abstract

Most existing multicast protocols adopt a static retransmission scheme (unicast or multicast) to retransmit lost packets. In the mobile multicast environment, static multicast retransmission mode may lead to congestion in the receivers' wireless interfaces, while static unicast mode may result in great network load. Both static unicast and multicast retransmission modes will cause a performance loss. This paper logically divides the mobile multicast network into fixed and mobile parts, and focuses on the mobile part. Then this paper analyzes the retransmission costs when multicast or unicast mode is chosen. Two main parameters are used to compare their efficiencies: the average air-interface utilization of each receiver and the average network load. Based on the results of analysis, two new algorithms, called NLPA (Network Load Priority Algorithm) and AUPA (Air-interface Utilization Priority Algorithm) are presented. Finally, simulation results conclude that, with proper parameters, both NLPA and AUPA can dynamically alternate between unicast and multicast retransmission modes according to the conditions of network and receiver, and avoid congestion in receivers' wireless interfaces as well as great network load, with a better use of network and terminal resources.