As seen, after the PBX sends an INVITE out, a 183 w/SDP comes back from the ITSP which is sent through the SBC to the PBX.
The PBX then waits for about 30 seconds, before sending a CANCEL message.
Expanding on the Reason Code, ‘recovery on timer expiry’ is indicated.
If the PBX must receive a 180 instead of 183 then, simply use the channel variable ‘ignore_early_media=ring_ready’ to force a 180 to be sent to the PBX.
For the dial plan (the one used to send calls to the ITSP from the PBX), this is what you enter:
If you are using the ‘advanced dialplanrouting’ dialplan routing’ with regular expression, use the following and insert above the ‘bridge’: