This looks to be specific to re-broadcasting (which I haven’t had the pleasure 
of playing with yet)

Looking at the diagram in there. I assume you configure a new source with a 
multicast address on your MOH server.
If it’s set to re-broadcast, it’ll be looking to capture the input stream from 
that address.

Is it just saying since your MOH server is receiving MMOH on say 239.1.1.1:16384
(And would then re-broadcast this as Unicast where required)
It won’t send any multicast on that same address

But you can configure a multicast address – on that source – which means it 
re-broadcasts the original stream as multicast on a new multicast address as 
well.

MoH server for re-broadcasting + External Multicast source must be on same LAN 
(or at least have multicast routing connectivity between them) for the 
rebroadcasting – so if your server is receiving on one address, you wouldn’t 
want to be sending out on the same address.

That’s the way I read it which I think makes sense to me.

Cheers,

Tim

From: cisco-voip <[email protected]> On Behalf Of Anthony 
Holloway
Sent: Thursday, 19 September 2019 1:00 AM
To: Cisco VoIP Group <[email protected]>
Subject: [cisco-voip] Multicast MOH (MMOH) SRND Question

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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