PIM Sparse Mode (PIM-SM) is designed for networks where multicast group members are sparsely distributed. It operates on a pull model, meaning multicast traffic is not flooded; instead, routers must explicitly send Join messages to receive traffic.

To facilitate this, PIM-SM requires a Rendezvous Point (RP), which acts as a meeting place for sources and receivers. Traffic initially flows down a shared distribution tree (rooted at the RP) to reach the receivers. In contrast, PIM Dense Mode uses a "push" (flood and prune) model and builds source-based trees by default.

Cisco Systems, IP Multicast: PIM Configuration Guide, "Protocol Independent Multicast (PIM)," Section: "PIM Sparse Mode".

Quote: "PIM-SM uses a pull model to deliver multicast traffic. Only network segments with active receivers that have explicitly requested the data will receive the traffic."

IETF RFC 7761, Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised), Section 3.1.

Summary: Defines the role of the Rendezvous Point (RP) and the creation of shared trees (*,G) for traffic distribution.

Juniper Networks, Multicast Protocols Guide, "Understanding PIM Sparse Mode".

Quote: "PIM sparse mode (PIM-SM) ... relies on a rendezvous point (RP) to forward multicast traffic ... builds a shared tree."