Abstract: PIM-SM（Protocol Independent MulticastSparse Mode）is currently the preferred intra-domain multicast routing protocol. Comparing with other PIM protocol, the switching from shared tree to the shortest path tree can effectively reduce the network delay and the load of RP. NS2 is an objectoriented simulator based on discrete event. It can availably simulate network topology and network data transmission. This article is to simulate the process of switching from RPT to SPT with NS2 and analyze the simulated data in detail. The result illustrates the superiority of the switch from RPT to SPT.

Key words: PIM-SM, RPT, SPT, simulation