[asterisk-dev] 13.24.1 / PJSIP: early media via 180 Ringing containing SDP is ignored

[Michael Maier]

On 24.01.19 at 12:08 Joshua C. Colp wrote:
> On Thu, Jan 24, 2019, at 7:00 AM, Michael Maier wrote:
>> Hello!
>>
>> Given is an outbound call to a callee via asterisk to the ISP. After 
>> INVITE, the ISP sends 100 Trying and some time later 180 Ringing *w/* 
>> SDP and the header
>> "P-Early-Media: sendonly" (no 183 or any other thing until callee 
>> responds). SDP in 180 contains media attribute *sendrecv* 
>> (contradicting to the P-Early-Media header).
>>
>> Asterisk 13.24.1 sends PRACK to the ISP (w/o SDP) and the 180 to the 
>> caller - but SDP is dropped and therefor no early media is possible!
>>
>> Is this behavior a bug or a feature?
> 
> It would be a bug. That's not a scenario that I think anyone has really tested or fully scoped out. Is media actually received while in the 180 with Ringing stage?
> 

Just a quick thought:
Would it be a valid workaround to enable inband_progress for the calling extension? This ensures, that a media session is always generated - especially for an incoming 180.
The question now is: if the ISP sends media and asterisk creates media itself (as it told) - which media is preferred? Will asterisk drop ISP's media in favor of its own
media? Or will it pass the ISP's media and drop own media?


Thanks,
Michael