End user has CUCM 11.5 and ISR 4321, currently for PSTN calls there is E1 with digital Trunk connected to ISR4321.
In short time end user will disconnect digital trunk and use SIP trunk, so now we are carrying out test with
a TEST sip trunk connected to the same ISR.
We configured the TEST SIP trunk on ISR , and config on CUCM the SIP trunk to ISR for outgoing calls and works fine, calls are completed without problems. But for incoming calls we are receiving error code 503 Service Unavailable
after checking some discussions we found that CUBE option must be enable and configure some dial-peers,
we tried a similar config but we still received error 503. We enable CUBE on ISR and follow this guide.
There must be some additional config on ISR and CUCM so that incoming calls on SIP Trunk can be completed when
on the same ISR there is working a H323 trunk to CUCM?
With a 503 error, the first thing I would look for is IP address/port number agreement between the SIP trunk to the CUBE and the CUBE itself, because that is the easiest thing to check.
The second thing I would look at is codec-mismatch issues. Remember that depending on early offer/delayed offer whether the initiator of the call or the target of the call does final codec selection will differ. You can view codec negotiation in your debug ccsip messages and also look in your CUCM trace file to see if CUCM is attempting to allocate a transcoder in the trace file.
If you post the output of debug ccsip messages here we can take a look. The CUCM trace file would also be helpful if you are willing to post that as well.