[asterisk-users] SIP INFO messages with Content-Type: application/media_control+xml

[Joshua C. Colp]

On Wed, Oct 13, 2021 at 10:05 AM Floimair Florian <f.floimair at commend.com>
wrote:

> Hi all!
>
>
>
> We have a WebRTC user-agent (using sip.js) that is giving me headache.
>
>
>
> When a different user-agent calls this user-agent, we frequently see
> Asterisk generating SIP INFO messages with
>
>
>
> Content-Type: application/media_control+xml
>
> Content-Length: 178
>
>
>
> <?xml version="1.0" encoding="utf-8" ?>
>
> <media_control>
>
>   <vc_primitive>
>
>    <to_encoder>
>
>     <picture_fast_update/>
>
>   </to_encoder>
>
> </vc_primitive>
>
> </media_control>
>
>
>
> In the payload, that is sent from Asterisk to the caller UA (the WebRTC
> client is the callee).
>
>
>
> While this does not do any harm usually, I have no clue yet what causes
> Asterisk to generate these INFO messages.
> I do know what they are for (https://datatracker.ietf.org/doc/html/rfc5168),
> but not why Asterisk is generating those or what might be the trigger.
>
>
>
> Anyone have any hint?
>

They will occur as a result of a video client requesting a full frame, and
there's a few places in Asterisk where it will generate one in certain
scenarios. Generally it comes from another client though. It can be
received either using an incoming INFO request, or via RTCP through a PLI
or FIR. If using PJSIP then the INFO request is only used for the H.264
codec if the WebRTC option is not enabled.

-- 
Joshua C. Colp
Asterisk Technical Lead
Sangoma Technologies
Check us out at www.sangoma.com and www.asterisk.org
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