The Single Source Multicast (SSM) model has received considerable attention from the research communityas it could finally bring a scalable solution for some multicast applications. In the SSM model it is the responsibility of the applications to tell the network what are their sources of interest. As a consequence, the SSM model is well suited for one to many multicast applications (such as TV and radio streaming) because there is only one source to discover and it is supposed to be well known. However there still does not exist an SSM session layer protocol and middleware in order to help Any Source Multicast (ASM) applications to discover the presence or departure of the SSM sources. In this paper, we propose a detailed architecture for such a source discovery session layer protocol. We have implemented our protocol as a middleware called Libemu and freely available as an open source library.