概述了组播路由协议。分析了协议独立的组播路由一稀疏模式（PIM-SM)的缺陷，提出多个会聚 点（RPs)的PIM-SM的改进机制。多个RPs机制有效地提高了原有单个RP的PIM-SM协议的健壮性，有利 于实现负载均衡、分类业务及提高系统的容错性能，并讨论多个RPs机制的开销问题。分析了 PIM-SM实现细 节和组播技术的前景。

This paper first explains why IP multicasting must be used. Then it summaries the fundamentals of IP multicasting and multicast routing protocols. After that it specially discusses protoool independent multicast-sparse mode (PIM-SM), points out its defect and proposes a scheme to solve it. In this scheme each source registers and sends data packets toward multiple rendezvous points (RPs) but receivers only join to a single RP. If one of the RPs fails, receivers will join to one of the alternative RPs quickly. On implementation, the paper centers on the details of implementing PIM-SM. Finally it discusses the problems and prospect of IP multicasting.