PIM-SM requires the following components: a Rendez-vous Point, shared trees, source trees.

PIM Register and Register Stop messages 

PIM register messages are sent by a PIM router to the Rendez-vous Point when it [the PIM router] receives multicast traffic from a streaming source. 

PIM RP sends a PIM register stop message to signal to the PIM router that it [the RP] has received the PIM register message.

Incoming Interfaces vs Outgoing Interface List

Incoming Interface

The PIM router’s interface that receives – or is supposed to receive – multicast traffic from the multicast source.