We have a Customer complaint that some inbound calls do not hear ring back, but get two way audio when the called party answers.
Upon further investigation, I determined the calls that get ring back is when the PBX PRI sends us an Alerting message, which is translated to SIP 180. When a call gets sent to a virtual extension in the PBX, the PBX request early media which is translated to SIP 183 with SDP. However, right after that we get an alerting message which propagates as SIP 180. NOTE: We do want the PBX to have the ability to send early media requests.
So how can I get the 908e to 'eat' the alerting message if it already received a request to open media from the PRI?
We have a couple ringback override options on the SIP trunk that might be helpful and worth a try. You will need to test out regular calls and the specific scenario to be certain. Here is what you will find on the SIP trunk:
TA908e(config-T01)#ringback override 180 - Override a 180 and send 183 with local ringback 183 - Override a 183 and send 183 with local ringback
This means if the ADTRAN is ready to send a 180, usually because we receive an Alerting on the PR side, we will send a 183 and generate ringback locally in rtp. This should help with cases where maybe the PBX is supposed to be providing ringback inband, but it does not for some reason. The ringback audio is only played out the SIP-side. So PRI to SIP, the PRI side does not get ringback from these commands.