Investigation in subsequent request problem in probe-based multicast admission control scheme

Multicast is an efficient approach to save network bandwidth for multimedia streaming services. To guarantee QoS for multimedia streaming services, while maintain the bandwidth efficiency of the multicast transmission, admission control is expected. In this paper, we study a probe-based multicast admission control (PBMAC) scheme, which was proposed to provide scalable and simple admission control for multicast services. It is observed that, in the scheme, a so-called subsequent request problem degrades system performance significantly when the network traffic is heavily loaded. An analytical model of subsequent requests problem is provided in this paper. Based on the analysis, an enhanced PBMAC (EPBMAC) scheme is devised to solve the problem. A new metric - normalized requested equivalent link capacity is defined to evaluate the performance of both PBMAC and EPBMAC. Simulation results validate the analytical models for PBMAC and EPBMAC. Analytical and simulation results show that the subsequent request problem is well solved with minor assistance from routers.