Operation Manual – MulticastH3C S5600 Series Ethernet Switches Chapter 4 PIM Configuration4-6multicast forwarding, and is suitable for large- and medium-sized networks withsparsely and widely distributed multicast group members.The basic implementation of PIM-SM is as follows:z PIM-SM assumes that no hosts need to receive multicast data. In the PIM-SMmode, routers must specifically request a particular multicast stream before thedata is forwarded to them. The core task for PIM-SM to implement multicastforwarding is to build and maintain rendezvous point trees (RPTs). An RPT isrooted at a router in the PIM domain as the common node, or rendezvous point(RP), through which the multicast data travels along the RPT and reaches thereceivers.z When a receiver is interested in the multicast data addressed to a specificmulticast group, the router connected to this receiver sends a join message to theRP corresponding to that multicast group. The path along which the messagegoes hop by hop to the RP forms a branch of the RPT.z When a multicast source sends a multicast packet to a multicast group, the routerdirectly connected with the multicast source first registers the multicast sourcewith the RP by sending a register message to the RP by unicast. The arrival of thismessage at the RP triggers the establishment of an SPT. Then, the multicastsource sends subsequent multicast packets along the SPT to the RP. Uponreaching the RP, the multicast packet is duplicated and delivered to the receiversalong the RPT.Note:Multicast traffic is duplicated only where the distribution tree branches, and this processautomatically repeats until the multicast traffic reaches the receivers.4.1.4 How PIM-SM WorksThe working mechanism of PIM-SM is summarized as follows:z Neighbor discoveryz DR electionz RP discoveryz RPT buildingz Multicast source registrationz Switchover from RPT to SPTz Assert
