[cisco-voip] CM Early Offer issue

[Justin Steinberg]

I have a situation where I am using the CM 8.6 SIP profile 'Early Offer
support for voice and video calls (insert MTP if needed)' on a SIP trunk
connection to the PSTN.  I am using this setting so that CM sends early
offer/early media as it is required by the SIP provider in order to
complete calls to certain numbers (typically seem to be IVRs).



One of our locations is in a CM region that is G729 to the CUBE region.
Therefore the calls between this site and the CUBE and ultimately the telco
softswitch are G729.  Most calls work fine as G729 and there are no issues.



With the above parameter enabled, the CM generated outbound early
offer only includes
G729.   The telco for our SIP trunk has another customer (maybe more) on
the same softswitch that only use G711.   We are unable to complete these
calls due to the codec mismatch.



Our CM cluster has transcoders available that sit in between the remote
site with the G729 requirement and the CUBE and could convert the G729 call
to G711, but that never happens since the Telco sends a 480 disconnect
message back without sending any SDP or invite to change the codec to G711.



Thus the call fails.



The telco states they have no transcoders available to address codec
mismatches on calls between their customers.   So ultimately, they are
trying to make this a customer issue by telling us that one of us must
change our customer equipment so that calls between us can agree on a
common codec.



Is there a way to use the above parameter and have CM send both G711 and
G729 in the early media so that the telco can pick ?  Since the remote site
placing the call is G729 to the CUBE, the only way CM could put a
G711 capabilities in the early offer would be to do so knowing that a
transcoder is available.   I am not sure if this is possible.



I am also not sure whether sending multiple codecs in an early offer/early
media is possible.


Has anyone come across a similar scenario?
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