PIM Source-Specific Multicast (PIM-SSM) is a variant of PIM-SM that builds trees that are rooted in just one source. SSM, defined in RFC 3569, eliminates the RPs and shared trees of sparse mode and only builds an SPT. SSM trees are built directly based on the receipt of group membership reports that request a given source. SSM is suitable for when well-known sources exist within the local PIM domain and for broadcast applications.
