[asterisk-users] Outbound call: caller gets no ringback on session progress

Joshua C. Colp jcolp at digium.com
Wed Dec 12 12:43:41 CST 2018

On Wed, Dec 12, 2018, at 12:31 PM, Michael Maier wrote:


> The problem: The extension doesn't create a ringback locally, because 
> it most probably expects it to
> be sent by the callee - but the callee doesn't send anything (not 
> surprising, because there has been
> no SDP).
> Or should Asterisk create the ringback (Asterisk doesn't send any RTP 
> package)? Or should the phone
> create the ringback itself because there is a 180 Ringing (even if it 
> contains SDP)?
> I'm wondering: Why does Asterisk create a 183 to the extension 
> containing SDP if the callee didn't
> provide any SDP?
> So many questions ... . Could somebody please shine some light on it? 
> What's going wrong here?

The core doesn't communicate whether progress includes media or not, so the PJSIP channel driver (and even chan_sip) assumes media is there. What should happen in chan_pjsip is that it would send inband ringing and not a 180 Ringing with SDP, but that is not currently implemented and I don't think this particularly interaction has come up before to cause it to be implemented. I'd therefore suggest raising an issue[1] with the SIP trace.

[1] https://issues.asterisk.org/jira

Joshua C. Colp
Digium - A Sangoma Company | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org

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