> Hi,
>
> >The key point of this discussion is how to find out the proper
> state of the rollback.
> >I think ,Some rules of using re-invite may be helpful.Such as, we
> restrict only
> >one offer/answer pair in a re-invite,
>
> I don't think we can do that, because at least some pre-condition
> scenarios require more offer/answer pairs.
>
> And, even if you would only allow e.g. a single UPDATE within the
> re-INVITE, you would still have the same question: if the UPDATE
> suceeds, but the re-INVITE then fails, what is the state?
>
There are some confuses of the offer/answer pair.
I consider negotiations of a new SDP or modification of former SDP
（not pre-condition） as one offer/answer pair,then pre-conditions
of the same SDP belong to the offer/answer pair caused by
the first offer/answer.
Anyway, If only one new SDP or modificaition and its pre-condition
negotiations are allowed in a re-invite，to find out the rollback
state becomes earier.
Regards
Eric.wang
> Regards,
>
> Christer
>
>
> "Christer Holmberg" <christer.holmberg@xxxxxxxxxxxx> 写于 2009-02-16 21:41:59:
>
> >
> > Hi,
> >
> >
> > >>I also pay high attention to the topic of "rollback of re-Invite".
> > >>As lots of service is implemented on the network using SIP, and
> > >>different ways may be carried out by different corporations, it's
> > necessary to define
> > >>a complete and clear method to solve the failure when the unsuccessful
> > re-Invite
> > >>happens.
> > >
> > >I agree, and we thought that having a generic rule, not related to
> > >specific use-cases, would be the most clear, clean and complete
> > >solution.
> > >
> > >[gaoyang] It is simple and clear. But it disregard nature property of
> > nested transaction. I concluded incorrectness and drawback of such way.
> > More details in
> > http://www.ietf.org/internet-drafts/draft-gaoyang-sipping-session-state-
> > analysis-01.txt.
> >
> > I agree it's not the most "beautiful" solution - that's why we spent a
> > long time discussing it.
> >
> > >>And the problems "Commit any session parameters that have been
> > sucessfully changed"
> > >>metioned in "draft-gaoyang-sipping-session-state-analysis-01.txt" need
> > further discuss,
> > >>I think.
> > >
> > >The draft does not define a generic rule. It more or less says that
> > >every time there is a new use-case, the offer/answer rollback aspects
> > >needs to be documented for that use-case. I think that is something we
> > >wanted to avoid.
> > >
> > >[gaoyang] It is not use-case oriented, but rules/definition oriented.
> > >And the definition of how o/a pairs form nested transaction should be
> > open for future.
> > >Such as "a=chain" and so on extension can form more o/a pairs as nested
> > transaction. It is not use-case.
> > >We can have a further talk.
> > >
> > >If I understand chapter 4.3.3 correct, it says that if you have a
> > >pending re-INVITE transaction, a NEW modification must be sent in a
> > >re-INVITE request. That way we would get rid of the race condition
> > >problem. That is an interesting point. I guess the question is whether
> > >it's too lake to make such a rule.
> > >
> > >[gaoyang] Is the "lake" late? I think it can be BCP, not rules :).
> >
> > Perhaps, yes.
> >
> > Regards,
> >
> > Christer
> >
> >
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