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Configure CUBE to send PRACK for early media


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.


Community Member

Configure CUBE to send PRACK for early media


what version of CUCM and CUBE are you running?

Early media in cube is enabled by default, unless you have this command "rel1xx disable" under your voice service voip > sip configuration.

I am currently working on an issue with a Verizon sip trunk where I had to disable Early media in order to get blind transfers to work with 2-way audio. Apparently a known issue with CUBE in 15.1.2T2.

Not having Early media obviously breaks other things like announcements and some IVR calls, still working with TAC about this.


Community Member

Configure CUBE to send PRACK for early media

Did you ever find a resolution to this?  We just upgraded to UCM 8.5 and were hoping to enable codec renegotiation, however when we uncheck 'require mtp' on the trunk we started see the blind xfers w/ one-way audio.  Our CUBE is running 15.1.2T1.


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