Combining precomputation and on-demand routing for multicast QoS routing

In QoS routing, two computational approaches have been studied: precomputation and on-demand computation. The precomputation approaches have the advantage of extreme efficiency in connection requests processing, but suffers from large storage overhead for maintenance of precomputed QoS routes. In contrast, the on-demand computation approaches have higher connection acceptance probability, but incur large per-request computation cost and long join latency. In this paper, we try to combine the two approaches in the design of a multicast routing protocol PPMRP (Probabilistic Precomputation Multi-cast Routing Protocol). PPMRP is the first attempt to include the precomputation technique in the design of multicast QoS routing protocols. It employs two innovative ideas to achieve a nice balance of cost and performance: scope-limited adverting of multicast tree information and probabilistic selection of precomputation routers. Through extensive simulations, we demonstrate that PPMRP exhibits the low join latency characteristic and superior connection acceptance probability without excessive computation and control message overhead.