Abstract: With the multicast technology gaining prominence and acceptance, its modeling and performance evaluation of the routing protocol has been an important problem of the computer network. PIM-SM (protocol-independent multicast-dense mode) protocol is a currently widely used intra-domain multicast routing protocol in the Internet. In allusion to the protocol characteristic of the complexity and asynchronism, the key mechanism of the protocol is analyzed in detail. It is presented a formal protocol description and is modeled based on the Petri net. The academic base of the protocol is provided for the performance analysis, system simulation and concrete implement.

Key words: Multicast, PIM-SM Protocol, Petri Net, Share Tree

摘要： 随着组播技术的飞速发展和广泛应用，对其路由协议进行数学建模和分析已经成为计算机网络领域一个重要的研究问题。其中PIM-SM协议是目前Internet上最广泛应用的域内组播路由协议。针对PIM-SM协议的复杂、异步的特点，在对PIM-SM协议机制详细分析的基础上，利用Petri网对其进行形式化描述和建模，为协议进行性能分析、系统仿真和具体实现提供理论基础。

关键词: 组播, PIM-SM协议, Petri网, 共享树