Hi Paul,
Before I get back to this thread, I find there has been many discussion here.
Please see inlines.
Thanks,
Gao
Paul Kyzivat <pkyzivat@xxxxxxxxx> 写于 2010-04-17 06:14:28:
> I think we are now down to the essence of the question:
>
> gao.yang2@xxxxxxxxxx wrote:
>
> > > Could you please show the text in 3261 which says that the SDP in an
> > > unreliable response is the SDP answer?
> >
> > [Gao]: text from RFC3261:
> >
> > o If the initial offer is in an INVITE, the answer MUST be in a
> > reliable non-failure message from UAS back to UAC which is
> > correlated to that INVITE. For this specification, that is
> > only the final 2xx response to that INVITE. That same exact
> > answer MAY also be placed *in any provisional responses sent*
> > * prior to the answer*. The UAC *MUST *treat *the first session*
> > * description it receives as the answer*, and MUST ignore any
> > session descriptions in subsequent responses to the initial
> > INVITE.
> >
> > And, considering UAS send SDP in unreliable response before the answer,
> > then the SDP would be the *the first session*
> > * description it receives*.
> >
> > RFC3261 using the word "AS THE ANSWER", not as if.
>
> At this point, we are arguing about the *intent* of the text - it is
> clearly confusing to some people.
>
> And AFAIK we (me, Gao, Shinji, and Christer) are all in agreement that
> the intent of the existing text is that:
[Gao] Yes.
>
> - *if* the UAC receives SDP in an unreliable response before
> receiving it in a reliable response, it MUST begin to use it
> in the same way that it would use it if that SDP had been
> received in a reliable response,
>
> - but that it is not officially "the answer", and so it is not
> yet permissible to initiate another o/a exchange until a reliable
> response containing "the answer" is received.
>
> - but when "the answer" is received, it MUST be ignored
> (rather than "used") if an earlier SDP has already been
> received and so "treated as the answer".
>
> Are *we* all in agreement that this is the one and only *intended*
> meaning of the text?
>
> Then the issue is that *someone else* (who Gao has had occasion to do
> interop testing with) is claiming that there is a different, yet
> legitimate, interpretation of the exiting text. Namely:
>
> - *if* the UAC receives SDP in an unreliable response before
> receiving it in a reliable response, it MUST begin to use it
> in the same way that it would use it if it had been received
> in a reliable response,
>
> - the UAC MUST (or SHOULD?) consider this SDP to be "the answer",
> and hence it MAY send another offer, even before receiving
> another copy of that answer SDP in a *reliable* response.
>
> - still it MUST ignore SDP in subsequent responses to the
> INVITE.
>
> If so, then the question comes down to:
>
> Is this alternate interpretation a valid and legitimate interpretation
> of the existing text, or not?
>
> I agree that this is a fair question to ask, and I am not yet settled on
> an answer to it.
[Gao] Mee too.
>
> I am approaching this in the manner of a mathematical proof by
> contradiction: If this alternative interpretation leads to some sort of
> inconsistency, then it is not valid. If we can find no inconsistencies,
> then it is a valid interpretation. And if it is, then the text is
> ambiguous and will require normative changes to fix.
[Gao] Yes. And thanks for your ratiocination.
>
> So, we can either seek out such an inconsistency, OR we can simply
> concede that the text is ambiguous and begin work on a normative
> correction to address it.
[Gao] I suggest do inconsistency analysis first, to avoid normative correction if it is unnecessary.
>
> I'm pretty sure that we are going to reach the same endpoint either way.
> So its a matter of whether we need a normative document to convince
> everyone or not.
>
> I'd appreciate feedback on my logic above.
>
> Thank you,
> Paul
>
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