Hi there,
Try to capture the issue yourself in real time and use the command "debug ccsip messages" in the first instance while troubleshooting. Compare the debugs of the working & non-working calls and check what differences there are, if any.
If you seek any further help here, you would need to provide more info on your setup, e.g. If you have CUCM and your integration with your CUBE (SIP or H.323).
Other specifics such as does it occur on inbound or outbound calls, or on both?
Also providing a copy of the running config of your CUBE with any sensitive info removed would also help.
There are numerous posts on the Support Community re SIP trunks to Deutsche Telecom, so may also be best to review these and find the one which is applicable to you.
