What protocol employs a pull model for sending multicast traffic?

The correct answer is PIM-SM (Protocol Independent Multicast - Sparse Mode), which employs a pull model for sending multicast traffic. In PIM-SM, when a host wants to receive multicast traffic, it sends a join message to the nearest multicast router. This initiates a process where the router pulls the multicast data from the source only when there is at least one receiver (or more) interested in that data. This means that multicast traffic is sent only after the group membership has been established, conserving bandwidth and ensuring efficient use of network resources.

PIM-SM is particularly well-suited for environments where multicast group memberships can be sparse—meaning that not all network segments will have members interested in the multicast traffic. This contrasts with protocols that might continuously send multicast traffic regardless of group membership, leading to inefficient use of network resources.

In contrast, other options like IGMP (Internet Group Management Protocol) are primarily used to manage group memberships rather than handling the multicast data transmission itself. RTP (Real-time Transport Protocol) is used for delivering audio and video over IP networks, but it does not specifically handle the management of multicast traffic distribution through a pull model. PIM-DM (Protocol Independent Multicast - Dense Mode) uses a push model