A quick run down of common causes for not receiving music on hold, symptoms include tone on hold or silence.
Multicast routing must in place across the entire path to the endpoint
receiving the MoH stream, the MoH server in CallManager must set the TTL value
to a high enough value to reach the endpoint, the default is 2 hops.
If the endpoint is connecting via the PSTN, the PSTN gateway must have the
"ccm-manager music-on-hold" command configured to stream multicast MoH to the
No MoH configured for the device putting the endpoint on hold, or invalid MoH source configured.
The MoH server selected by the endpoint's MRGL lacks the MoH source file, as
these must be uploaded to each server separately.
The location that the endpoint and/or MoH server reside in has reached the
maximum specified bandwidth, therefore the MoH stream is rejected by call
admission control (CAC). Note that Multicast MoH is exempt from CAC.
The region configuration for the endpoint and MoH server selected a CODEC
that MoH isn't transmitted in. By default MoH is only sent in G711 format, you
must enable G729 under the IP Voice App Streaming service parameters.
There must be no access lists that block the multicast MoH IP address (e.g.
126.96.36.199), or traffic from the MoH server's IP address in the case of unicast MoH.