hi John，
Sorry for replying so late . I have had my hands full these days.
I prefer no update with sdp outside INVITE/re-INVITE indeed,because
updates with sdp outside INVITE/re-INVITE can't be easily distinguished
from the pre-condition ones.
You said :
> It is implicit in the vast majority of
> cases, but timing issues break this, particularly where unreliable
> transport is concerned. For example, if UPDATE arrives while
> awaiting ACK, is it because UPDATE was sent before the ACK, or
> because the ACK was lost?
In rfc3261 13.3.1.4
"""The 2xx response is passed to the transport with an
interval that starts at T1 seconds and doubles for each
retransmission until it reaches T2 seconds (T1 and T2 are defined in
Section 17). Response retransmissions cease when an ACK request for
the response is received. This is independent of whatever transport
protocols are used to send the response."""
13.2.2.4 2xx Responses
"""The UAC core MUST generate an ACK request for each 2xx received from
the transaction layer."""
From above chapters, we can conclude that if the network is in work well, the
ACK will arrive.For the sender of new SDP, waiting to send a re-INVITE with
the new offer until the former re-INVITE ends is possible.And for the receiver ,
if he receives a new re-INVITE without receiving the former ACK, he may wait for
the ACK, or assume that he had received ACK and continue to process the new offer.
But i don't intend to eliminate update outside INVITE/re-INVITE, I just want to
avoid update with SDP outside INVITE/re-INVITE.
And if updates for session timer or other usages are without SDP, it can go outside
INVITE/re-INVITE.
regards
Eric.wang
"Elwell, John" <john.elwell@xxxxxxxxxxx> 写于 2009-02-17 23:01:34:
> Christer,
>
> I hope that is not what the authors are proposing, because UPDATE is
> certainly useful outside the context of INVITE/re-INVITE
> transactions, e.g., for session timer refreshes.
>
> John
>
> From: sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] On Behalf Of
> Christer Holmberg
> Sent: 17 February 2009 14:00
> To: Elwell, John; wang.libo@xxxxxxxxxx
> Cc: sipping@xxxxxxxx
> Subject: Re: [Sipping] About "rollback of re-Invite"
> Hi John,
>
> My understanding of the proposal is that you would only send UPDATEs
> if they ARE nested to the re-INVITE transaction. Otherwise you would
> send a new re-INVITE. That way you would know that an UPDATE is
> nested even if it arrives after the ACK.
>
> That of course means that the ongoing re-INVITE transactions needs
> to finish first (either by itself, or by being cancelled).
>
> But, I may have missunderstood, so it's better if the authors speak
> for themselves :)
>
> Regards,
>
> Christer
>
> From: Elwell, John [mailto:john.elwell@xxxxxxxxxxx]
> Sent: 17. helmikuuta 2009 15:51
> To: Christer Holmberg; wang.libo@xxxxxxxxxx
> Cc: sipping@xxxxxxxx
> Subject: RE: [Sipping] About "rollback of re-Invite"
> I haven't been following all of this discussion, but there is
> nothing explicitly to bind an UPDATE transaction to a parent INVITE
> or re-INVITE transaction. It is implicit in the vast majority of
> cases, but timing issues break this, particularly where unreliable
> transport is concerned. For example, if UPDATE arrives while
> awaiting ACK, is it because UPDATE was sent before the ACK, or
> because the ACK was lost? If UPDATE arrives before sending a final
> response to re-INVITE, is it because UPDATE is nested within the re-
> INVITE transaction, or has there been a CANCEL request that has been
> lost and will be repeated later? Without explicit binding, the only
> consistent thing to do is to treat each transaction separately, and
> not roll back. If this means pre-conditions are broken, the focus
> should be on fixing pre-conditions somehow.
>
> John
>
>
> From: sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] On Behalf Of
> Christer Holmberg
> Sent: 16 February 2009 18:00
> To: wang.libo@xxxxxxxxxx
> Cc: sipping@xxxxxxxx
> Subject: Re: [Sipping] About "rollback of re-Invite"
> 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?
>
> 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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