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

[Paul Kyzivat <[e-mail]>]

Hi Jonathan!

On 4/21/26 5:02 PM, Jonathan Lennox wrote:
> 
>>> The question is whether, if we get
>>> Offer: BUNDLE(a, b)
>>> PR-Answer: BUNDLE(a, b)
>>> Answer: No bundle
>>
>> I'm not familiar with the term "PR-Answer". I presume this comes from 
>> webrtc rather than sip. I'm thinking the sip-analog to this would be a 
>> reliable provisional response containing an answer. An exchange like 
>> that is probably an invalid use of offer/answer in sip. Specifically, 
>> once an answer is returned in a reliable provisional response to an 
>> offer in an INVITE it must remain unchanged in subsequent responses to 
>> that INVITE. (See section 2.2 of RFC 6337.)
>>
>> It would be helpful to see more detail - the message bodies from the 
>> exchange.
> 
> See https://datatracker.ietf.org/doc/html/rfc8829#section-4.1.10 
> <https://datatracker.ietf.org/doc/html/rfc8829#section-4.1.10> for a 
> definition of a WebRTC provisional answer.
> 
> In particular, it’s notable that one of the use cases described there is 
> the “serial forking” case, i.e. cases where in SIP various provisional 
> answers would have arrived on different dialogs.
> 
> As such, I think for WebRTC there can't be any constraints imposed on 
> what’s in the pr-answer vs. what’s in the final answer (or in a 
> subsequent pr-answer), because they might be coming from entirely 
> separate peers, and that’s an intended use case.

That is also a possibility in sip. In the case of forking, each fork 
establishes a separate provisional dialog, and all the offer/answer 
rules are applied separately in each. My prior comment assumed a single 
dialog.

More details would help sort it out. But it sounds like Harold is 
talking about a hypothetical case for which there is no more dialog.

	Thanks,
	Paul