Source-Specific Multicast (SSM) has been discussed as realistic multicast communication architecture used in the Internet. Due to the SSM conformance, source discovery procedure is eliminated from multicast routing protocol, and the protocol scalability is improved. However, because of no source address validation mechanism on the router side, multicast router cannot recognize un-trustworthy join requests and cannot avoid invalid or unavailable routing tree construction.

In this document, after studying the problems of SSM deployment, we propose a new communication model between multicast routers and multicast session directory systems. As a candidate of the session directory system, we propose to enhance Channel Reflector, which is a multicast channel announcement system maintaining (S,G) channel information for end users. Since it provides an effective policy and scope management, multicast routers cooperating with this system can validate (S,G) join and optionally translate (*,G) join to appropriate (S,G) joins.