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

[Michael Maier]

On 12.12.18 at 19:43 Joshua C. Colp wrote:
> On Wed, Dec 12, 2018, at 12:31 PM, Michael Maier wrote:
> 
> <snip>
> 
>>
>> 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. 

Another question: is there any use case for 183 Session Progress w/o SDP? IOW: Is a 183 Session
Progress just a bug of the ISP? If so, problem could be solved by dropping each 183 package w/o SDP.


Thanks,
Michael