Our company manufactures a custom SIP endpoint.
We have a customer who is having trouble answering incoming calls from the PSTN over a PRI. When they attempt to answer the call with our device, the endpoint responds to the INVITE from CUCM with an OK which includes a SDP message body. CUCM proceeds to ACK, without a SDP message body, the OK and follows it with a BYE stating reason "Q.850; cause=47" (Resource unavailable, unspecified).
If a call is placed to the same DN internally from a Cisco endpoint, our device has no issue answering the call. After our device responds to the INVITE with an OK, CUCM sends and ACK including a SDP message body and the media session begins.
I'll add that the customer doesn't have any issue dialing out across the PRI from our device.
I haven't had any luck trying to duplicate this issue with our own CUCM system. A key difference between our system and the customer's is the fact that our 2911 gateway only has a POTS interface where as the customer is using a PRI. I don't know for fact whether or not this is the cause of the issue but it's the biggest difference I see between the two systems.
What resource is unavailable or unspecified?