SSM

[Ali Boudani <aboudani@irisa.fr>]

Hello,
In the draft :

 A Framework for Source-Specific Multicast Deployment
                 <draft-bhattach-ssm-framework-01.txt>
 3. Limitations of Current Service Model
   There exist several service model limitations associated with ASM:
   A) Handling Well Known Sources via Shortest Path Forwarding
       In cases where the address of the source is well known in advance

      of the receiver joining the group, and when the shortest
      forwarding path is the preferred forwarding mode, then shared tree

      mechanisms and MSDP only represent unnecessary interim mechanisms,

      contributing to join latency and operational overhead.

So in which cases address of the source is well known in advance of the
receiver joining the group??
can u give me a simple example ??
just I want to understand it well.
thanx