[cisco-voip] Multicast MOH (MMOH) SRND Question

[Anthony Holloway]

I was helping someone troubleshoot a MMOH issue and what was happening was
that CUCM audio source, MOH Server, and MRG were all setup to do MMOH.
There was also a hardware MOH device on the network, which was sending MMOH
on the same IP address (239.1.1.1) as the CUCM MOH Server.

When I pointed out that this would be a problem, I was shown the following
statement from the SRND:


*"If the multicast MoH server and the audio source are configured with the
same multicast group address, when Phone B is placed on hold, it will
receive the multicast RTP audio stream (E) from the original multicast
stream (B) broadcast by the SRST router. In this case the MoH server does
not send the audio because it is aware that the destination multicast IP
address group is the same as the external audio source multicast stream (B)
broadcast by the SRST router."*

Source:
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab11/collab11/media.html#pgfId-1393039

Now, a TAC case was opened, and TAC said it should have done what the SRND
is stating, but I am doubtful.  I think the wording in the SRND is poor,
and that perhaps it only pertains to the Fixed source of 51, and not just
any source you create.

So, I'm asking for your understanding and knowledge of how this works, to
clarify this aspect of MMOH for me.  Please read the entire section of the
SRND linked, because context is important here.  I only provided a snippet.
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