In an autonomous system (AS) with reachable unicast routes, you can enable basic functions of PIM-SM so that user hosts can receive multicast data from any multicast source.
By default, the Rendezvous Point (RP) and the DR at the group member side immediately perform the shortest path tree (SPT) switchover after they receive the first multicast data packet. If a receiver wants to perform the SPT switchover only when the rate of multicast data packets reaches the threshold, you need to configure triggering conditions for the SPT switchover.
When an intranet and the Internet are divided into two independent multicast domains by a NAT device, you can configure multicast NAT to allow intranet receivers to demand Internet resources.