Enable Source Specific Multicast (SSM) to optimize PIM-SM by simplifying the many-to-many model (servers-to-receivers). Because most multicast applications distribute content to a group in one direction, SSM uses a one-to-many model that uses only a subset of the PIM-SM features. This model is more efficient and reduces the load on multicast routing devices.
SSM is a global configuration. After you enable SSM on a switch, it is enabled on all interfaces that run PIM. On an SSM-enabled switch, SSM behavior is limited to the SSM group range. For non-SSM groups, the protocol behavior is PIM-SM.