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[AVTCORE] Re: BUNDLE question - relationship to PR-Answer?

Roman Shpount <roman@telurix.com> Wed, 22 April 2026 15:04 UTC

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From: Roman Shpount <roman@telurix.com>
Date: Wed, 22 Apr 2026 11:03:41 -0400
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To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: [AVTCORE] Re: BUNDLE question - relationship to PR-Answer?
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Paul,

On Wed, Apr 22, 2026 at 10:34 AM Paul Kyzivat <pkyzivat@alum.mit.edu> wrote:

> The original question didn't say whether the PR-Answer and Answer were
> in the same fork or different forks.
>
> *If* they are in different forks then then I agree.
>
>
There is no SIP dialog or fork concept in WebRTC. Only offer/answer. It is
a pure SDP negotiation interface that can be used to implement SIP or other
signaling protocols. The concept of PR-Answer came from mapping multiple
SIP dialogs to a single offer/answer negotiation session. So, the PR-Answer
and Answer were different in the same SIP dialog; this would be an error.
If they are not in the same dialog, then it is legal and will need to be
mapped to the WebRTC API somehow. The only way this works is that each new
PR-Answer or Answer, if it differs from the previous PR-Answer, is treated
independently, as if it came from a new dialog, and that previous answers
were never received. WebRTC needs to roll back the negotiation state and
restart negotiation.

Best regards,
_____________
Roman Shpount

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