The main missing feature with SSM is automatic source discovery in multi source applications. If we consider that some domains might deploy SSM only (no ASM), it is necessary to have this feature implemented in end hosts. We have specified and implemented a new application protocol called SSMSDP (Source Specific Multicast Source Discovery Protocol). In this solution, a multi source session is identified by a control channel (C, G). Session receivers listen to this control channel. Sources send announcements to the controller (C). These announcements are then forwarded into the control channel. This allows receivers to learn about new sources and to join the corresponding SSM channel. The controller can be seen as some kind of RP but at the session level, and only for signalling.

The implementation of SSMSDP consists in a low level library aimed at offering at least the same functionality that ASM in the network does. We have developed a tool called “ssmsdpifier” based on this library. This tool allows the users to launch ASM applications (that is applications developed to run with ASM multicast), to be launched over SSM-only networks without patching/recompiling. Several well-known applications have shown to function without problems, including vic, rat and the multicast beacon.

Note that the lack of MLDv2 support in some operating systems (notably MS Windows) is currently limiting IPv6 SSM usage.