We are currently attempting to configure a CUBE/CUCM setup to send a PRACK message back to the SP via a SIP trunk. I have followed all the documentation which I can find, and can see the CUCM is sending a PRACK message to the CUBE, but no PRACK is then sent on from the CUBE to the SP.
The call flow is as follows:
Mobile/PSTN phone > SIP Trunk > CUBE > CUCM (SIP trunk between CUBE and CUCM) > SCCP IP Phone
We have configured CUCM to send PRACK by setting the SIP Rel1xx Options drop down to 'Send PRACK for all 1xx messages', while also de-selecting the MTP for the SIP trunk and ensuring that the 'disable early media on 180' check box in the SIP profile is un-ticked. CUCM does then send PRACK to the CUBE.
My question is what do we need to configure on the CUBE? The documentation which I have found so far seems to say that PRACK for early offer is supported, but we cant seem to get it to work.
Any help would be appreciated.