A network engineer must design a multicast solution based on these requirements: - interactive communication - must not use source trees - users must register - 100 multicast sources Which solution…

Any-Source Multicast (PIM-SM) typically switches from a shared tree to a shortest path tree (source tree) once data starts flowing, which violates the "must not use source trees" requirement.

MSDP is a control plane protocol used with PIM-SM to allow RPs in different PIM-SM domains to discover active sources, and it does not define the tree-building mechanism itself.

BIDIR-PIM is specifically designed for many-to-many interactive applications with a large number of sources and receivers. It builds only bidirectional shared (*,G) trees, meaning it never switches to source-specific (S,G) trees, which directly addresses the requirement to not use source trees.

PIM-DM builds source trees by flooding traffic throughout the network and then pruning branches without receivers, which directly contradicts the requirement to avoid source trees.