180 Ringing issue on tandem PJSIP trunks

[edailey]

Asterisk 20.5.2

We use Asterisk as an SBC between our customer’s PBX and our Twilio telephony back-end.

We have an issue on outbound calls from our Twilio application to certain numbers through our Asterisk SBC and out the customer PBX. The issue is that the Twilio caller often does not hear ringback. They wait and then disconnect the call because they think that the call failed, when it really didn’t.

When ringback is heard by the Twilio caller, the customer PBX sends us a 180 Ringing (No SDP). Asterisk sends the 180 Ringing on to Twilio and we then play the ringback locally. (no early media)

In the case of ringback failure, it is an early media scenario. Asterisk receives a 180 Ringing with SDP from the customer PBX. And then Asterisk sends a 183 Session Progress with SDP to Twilio.

What I would like to do is have Asterisk send a 180 Ringing with no SDP to Twilio, regardless of whether we receive a 180 Ringing with or without SDP.

I’ve tried a few settings in both PJSIP and Extensions, but nothing I do has changed this behavior.

Any thoughts?

[david551]

Dial option “r”. NB this is regardless of whether you receive 180.

[edailey]

Problem solved! I was able to get the result I wanted by putting an Answer step before the Dial step. I am curious about david551’s answer, though. Think I’ll try that, too.