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Re: [Sipping] About offeranswer draft:



So, what is it actually that you want to correct?


From: gao.yang2@xxxxxxxxxx [mailto:gao.yang2@xxxxxxxxxx]
Sent: 16. huhtikuuta 2010 8:44
To: Christer Holmberg
Cc: Paul Kyzivat; sipping@xxxxxxxx
Subject: RE: [Sipping] About offeranswer draft:


Hi,

But as we know, O/A draft is just for clarification, not for correction.

Thanks,

Gao

===================================
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Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>

2010-04-16 13:39

收件人
"gao.yang2@xxxxxxxxxx" <gao.yang2@xxxxxxxxxx>, Paul Kyzivat <pkyzivat@xxxxxxxxx>
抄送
"sipping@xxxxxxxx" <sipping@xxxxxxxx>
主题
RE: [Sipping] About offeranswer draft:






Hi,

>My previous mail to Christer is about the same topic.
>                
>                
>To be honest, your agree almost all of your reply. And I once have the same understanding of RFC3261.
>But when I reviewed again during the interworking-testing(in new interworking-testing, we always face some new equipment and hear some new understanding of RFC3261 from them), I feel it seams need correction.

That is why we are working with the o/a draft, which hopefully will clarify things for people.

Regards,

Christer



               
                Thanks,
               
                Gao
               
                ===================================
                Zip    : 210012
                Tel    : 87211
                Tel2   :(+86)-025-52877211
                e_mail : gao.yang2@xxxxxxxxxx
                ===================================
               
               
               
                Paul Kyzivat <pkyzivat@xxxxxxxxx>

                2010-04-15 22:59

                                 
                                 收件人
                                 gao.yang2@xxxxxxxxxx
                                 抄送
                                 Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>, "Somogyi, Gabor (NSN - HU/Budapest)" <gabor.somogyi@xxxxxxx>, OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>, "sipping@xxxxxxxx" <sipping@xxxxxxxx>
                                 主题
                                 Re: [Sipping] About offeranswer draft:

                                 




                inline
               
                gao.yang2@xxxxxxxxxx wrote:
                >
                >
                > sipping-bounces@xxxxxxxx 写于 2010-04-15 04:38:21:
                >
                >  > Hi,
                >  >
                >  > >> In your chart SDP4 is a reliable answer. Therefore SDP5 might be
                >  > >> interpreted as a new offer, hence UAC could send an answer in PRACK.
                >  > >> Quite similarly to 3PCC cases, where 200 contains the offer and
                > ACK the
                >  > >> answer.
                >  > >
                >  > >That has been investigated. Its not allowed. (Unfortunately I cannot
                >  > >recall the chain of reasoning that derived its illegality - it wasn't
                >  > >obvious but it was sound. It was worked out a *long* time ago.)
                >  >
                >  > The rule we have agreed to is very simple: at most one offer/answer
                >  > exchange per SIP transaction.
                >
                > Yes, it is. And what I talked here is also under this basic rule.
                >
                >  >
                >  > Whether it's clearly specified somewhere needs to be checked, though.
                >  >
                >  > I know there are implementations that "update" the SDP answer from
                >  > one reliable response to another (within the same transaction), for
                >  > the same transaction, but that is certainly nothing we have
                > standardized.
                >
                > I think it should be mentioned here, what is the *lawful* answer?
                > It is the one in the first reliable response.
                >
                > As it is the *lawful* answer, I think the UAC should using it when it
                > get the answer. And this seems *should* be made normative.
                > While how UAC handle SDP(from UAS) before the real answer, it can be BCP
                > issue.
               
                I think you are arguing that it is "lawful" for the UAS to send
                differing values for the SDP successive unreliable responses and in the
                subsequent reliable response. And that it is then the responsibility of
                the UAC to make this work "right" and "deterministically" by honoring
                the first and ignoring the subsequent ones. Is that right?
               
                But that makes no sense. The UAS cannot know if the UAC will receive the
                first, or any of, the unreliable responses. So if it were to do this odd
                behavior it must be satisfied that *any* of then are the one that the
                UAC uses. Or else it must be assuming that the UAC *might* use one or
                more of the unreliable ones, and eventually *switch* to the one in the
                reliable response.
               
                But 3261 is clear that the UAC should use the first one it receives, and
                ignore the remainder, *including* the reliable one. There is no
                provision for *switching*.
               
                Hence, its a corollary that the only behavior that the UAC can follow
                that is valid and consistent in the face of loss of unreliable responses
                is for them all to contain the same SDP. So that is the *lawful*
                behavior - a UAS that violates this is unreasonable.
               
                                Thanks,
                                Paul
               
               
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