You may have ringback for some calls, but not others. The difference in the SIP signaling is that you may find that the carrier might be sending a 183 PROGRESS, rather than a 180 ringing. For the SBC to allow the ringback to come from the carrier, then we need to make sure the Audiocodes SBC is set to support PRACK.
- Login to the Audiocodes
- Set your view to advanced
- Expand SIP Definitions > Click General Parameters
- Set PRACK Mode to “Supported”
- Click Apply
- Click Burn
- Expand Coders and Profiles
- Click the Carrier/ ITSP
- Change PRACK mode to Optional