Customer case 06Fax failing on T.38 negotiation
Retained CUCM traces surfaced the remote server's rejection long after CUCM had deleted its own.
- 1
Situation
A customer's fax wasn't working: T.38 was never negotiated after the call established on G.711. The CUCM logs had already been deleted.
- 2
What the data showed
The SIP ladder, built from the CUCM traces FRINK had kept, still showed the remote fax server answering the T.38 re-INVITE with "488 Not Acceptable Media". The CUBE call records named the dial-peers in use, and the CUBE running configuration confirmed T.38 was allowed on this side.
CUCM · SIP ladder with message content - 3
Resolution
With the local configuration verified and the rejection coming from the far end, the problem pointed firmly at the remote fax server.