Re: [Sipping] Liaison Statement on offer/answer procedures
"Christer Holmberg" <christer.holmberg@ericsson.com> Thu, 05 June 2008 05:19 UTC
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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: "Sanjay Sinha (sanjsinh)" <sanjsinh@cisco.com>, "Paul Kyzivat (pkyzivat)" <pkyzivat@cisco.com>
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Cc: "Elwell, John" <john.elwell@siemens.com>, sipping List <sipping@ietf.org>, Gonzalo Camarillo <gonzalo.camarillo@ericsson.com>, Mary Barnes <mary.barnes@nortel.com>
Subject: Re: [Sipping] Liaison Statement on offer/answer procedures
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Hi, >If precondition is treated as a separate case, then are there other use cases where UAS would need to send answer in provisional response to re-Invite. IMO, in majority of cases 200 OK would >carry answer to offer in re-Invite/UPDATE. I agree. I am not aware of other use-cases. And, even if there are other use-case, I still think that in the majority of those the SDP offer of the re-INVITE request itself will carry the "main" media changes. I don't think you would normally add streams etc using the intermediate UPDATE/PRACKs. Regards, Christer >-----Original Message----- >From: sipping-bounces@ietf.org >[mailto:sipping-bounces@ietf.org] On Behalf Of Paul Kyzivat (pkyzivat) >Sent: Wednesday, June 04, 2008 6:40 PM >To: Christer Holmberg >Cc: sipping List; Elwell, John; Gonzalo Camarillo; Mary Barnes >Subject: Re: [Sipping] Liaison Statement on offer/answer procedures > >Regarding SDP: > >I think the likely candidates are: > >1) as specified in 3261, and contrary to 3264, if a reinvite fails, the >SDP/media-session state rolls back to what it was before the reinvite. >This is so even if there answers were transmitted reliably via PRACK >and/or UPDATE. > >2) Once an answer has been transmitted reliably, it is committed, and >is not rolled back if the reinvite subsequently fails. > >Of these, (2) is probably easier to understand and implement. >And its probably semantically reasonable, except for one case: > >That case relates to preconditions. Using preconditions, you can get >into a state where an offer/answer has completed, but preconditions >have not been satisfied, so the media stream is not usable. It is then >expected that a subsequent o/a exchange will improve upon this, and >eventually result in usable media streams. If each o/a is committed >independently, then a previously working can be replaced with an >unusable state until a further o/a fixes it, and if a further o/a >doesn't fix it then it remains permanently broken. > >(An example of this might be starting from a working low bandwidth >audio session. A reinvite is then sent with an attempt to upgrade to a >wideband codec with preconditions used to condition the change on >obtaining sufficient bandwidth. In this case you would like to continue >to use the low bandwidth codec until you know if you have obtained the >resources for the wideband.) > >Note that this problem exists even without reinvite. It can occur if an >update to a working session is initiated using UPDATE with >preconditions. > >IMO this is an intrinsic problem with preconditions. Because they >aren't widely used, it may be prudent to split off fixing that as a >separate task. If that is done, then I think (2) above is probably a >good way to solve the rest of the problem. > >To solve the precondition problem I think we need a concept like >o/a-transaction. A single o/a pair is an o/a-transaction if it contains >no unsatisfied preconditions. But an o/a that has unsatisfied >preconditions results in an incomplete o/a-transaction. Additional o/a >pairs continue to be part of it until a final o/a pair where the >preconditions are satisfied. That ends the o/a-transaction. A failure >in the midst of an o/a-transaction (signaled in the enclosing protocol >like >sip) would revert to the session state in effect before the beginning >of the o/a-transaction. > >I would expect this direction for preconditions to be controversial. >(Among the one or two people who actually care about >preconditions.) Which is a good reason to split it off from the rest. > > Thanks, > Paul > >Christer Holmberg wrote: >> Hi, >> >> I agree with Paul that we probably aren't talking about >changes to 3264 here. >> >> Also, I am fine if we want to decouple "committings" of >media data/SDP updates with other types of data updates (contact etc). >> >> But, that means that we need to specify specific >"committing" rules for any type of data which can be affected. >Or, we can of course have a "default committing rule" (e.g. >full rollback), and then specify different rules for specific type of >data when/if needed. >> >> But, for the SDP data, would anyone object to a full rollback? >> >> Regards, >> >> Christer >> >> ________________________________ >> >> From: Paul Kyzivat [mailto:pkyzivat@cisco.com] >> Sent: Wed 04/06/2008 17:32 >> To: Gonzalo Camarillo >> Cc: Christer Holmberg; Elwell, John; sipping List; Mary Barnes >> Subject: Re: [Sipping] Liaison Statement on offer/answer procedures >> >> >> >> Gonzalo, >> >> I generally agree with your characterization below. But as I see it >> there likely are no changes needed to 3264. It is intentionally >> focused on the SDP, and not the conveyance of the SDP in some >> containing protocol. The following is about the extent of it in 3264: >> >> Protocol operation begins when one agent sends an >initial offer to >> another agent. An offer is initial if it is outside of >any context >> that may have already been established through the higher layer >> protocol. It is assumed that the higher layer protocol provides >> maintenance of some kind of context which allows the various SDP >> exchanges to be associated together. >> >> The agent receiving the offer MAY generate an answer, or it MAY >> reject the offer. The means for rejecting an offer are >dependent on >> the higher layer protocol. The offer/answer exchange is >atomic; if >> the answer is rejected, the session reverts to the state >prior to the >> offer (which may be absence of a session). >> >> SIP messed this up somewhat with the offerless-invite, and more when >> it introduced PRACK and UPDATE. The offerless-invite creates a case >> when it is impossible to reject an offer. But we aren't discussing >> that case here. Without PRACK and UPDATE, and with an offer in the >> INVITE, it the success or failure of the INVITE that determines the >> acceptance or rejection of the offer. (With an offerless invite, the >> ACK always accepts the offer, for better or worse.) >> >> The use of PRACK and UPDATE while an INVITE transaction is >is progress >> creates an ambiguous situation due to the following from >section 14.1 >> of >> 3261: >> >> If a UA receives a non-2xx final response to a >re-INVITE, the session >> parameters MUST remain unchanged, as if no re-INVITE had >been issued. >> >> This implies that changes made via PRACK and UPDATE during >the INVITE >> transaction must be rolled back. Since the problem created >by 3262 and >> 3311, in conjunction with 3261, I think the fixes will have to apply >> to those, not to 3264. >> >> Also, the issue about changing Contact addresses clearly has nothing >> to do with 3264. And I am becoming increasingly convinced that the >> rules for "committing" a change of Contact address ought to be >> decoupled from the rules for "committing" a change to media sessions. >> >> Before we get into the specifics, does the above make sense? >> >> Thanks, >> Paul >> >> >> >> Gonzalo Camarillo wrote: >>> Hi, >>> >>> we should be providing 3GPP with an answer to their liaison soon: >>> >>> https://datatracker.ietf.org/liaison/444/ >>> >>> The thing is that when working on the offer/answer usage >draft below, >>> we kept from making normative changes to offer/answer: >>> >>> >http://www.ietf.org/internet-drafts/draft-ietf-sipping-sip-offeranswe >>> r-08.txt >>> >>> >>> However, it seems that there are a few cases that would require >>> normative updates to RFC 3264. In this thread, two cases have been >>> identified: roll back and address changes during ongoing >>> transactions. I would like to see a list of such pending updates in >>> order to decide whether we need to revise RFC 3264 at this point or >>> document the current issues (like we are doing with RFC >3261) for a future update. >>> >>> Thanks, >>> >>> Gonzalo >>> >>> >>> >>> Christer Holmberg wrote: >>>> Hi, >>>> >>>> I do NOT think John's case is connected to the rollback issue. >>>> >>>> The rollback issue is: what happens to data that has been updated >>>> between the re-INVITE request and failure response? It of course >>>> included the target, but is not related to where responses >are sent. >>>> >>>> Responses are, afaik, always sent to where the request >came from, so >>>> if one updates the local target he has to make sure that >he listens >>>> to the "old" port if there are ongoing transactions. >>>> >>>> Regards, >>>> >>>> Christer >>>> >>>> >>>> >>>> ________________________________ >>>> >>>> Lähettäjä: Paul Kyzivat [mailto:pkyzivat@cisco.com] >>>> Lähetetty: pe 16.5.2008 14:38 >>>> Vastaanottaja: Elwell, John >>>> Kopio: Christer Holmberg; sipping List >>>> Aihe: Re: [Sipping] Liaison Statement on offer/answer procedures >>>> >>>> >>>> >>>> John, >>>> >>>> This is a good point. >>>> >>>> It does expose a potentially long window when address changes are >>>> problematic. I guess if a quick address change is >necessary then the >>>> INVITE, or reINVITE, can be CANCELed. >>>> >>>> IMO this is starting to identify an area that could stand to have >>>> more specification. I guess this sounds like a best >practices draft, >>>> but its still a little fuzzy to me. And I am far from >clear whether >>>> this is tightly connected to the o/a rollback issue. >>>> >>>> Thanks, >>>> Paul >>>> >>>> Elwell, John wrote: >>>>> Paul, >>>>> >>>>> >>>>>> -----Original Message----- >>>>>> From: sipping-bounces@ietf.org >>>>>> [mailto:sipping-bounces@ietf.org] On Behalf Of Paul Kyzivat >>>>>> Sent: 15 May 2008 14:48 >>>>>> To: Christer Holmberg >>>>>> Cc: sipping List >>>>>> Subject: Re: [Sipping] Liaison Statement on offer/answer >>>>>> procedures >>>>>> >>>>>> Christer, >>>>>> >>>>>> Saying "you shouldn't do it" to changing contact address >or media >>>>>> address ignores facts of life that may require doing it. This >>>>>> overlaps strongly with the session mobility discussion that is >>>>>> currently going on. >>>>>> >>>>>> Specifically, if a UA is losing possession of its address, or >>>>>> connectivity via that address, then it will have to do >>>>>> *something*. If we are going to say that you shouldn't >change the >>>>>> contact address in a dialog, and shouldn't change the media >>>>>> address in a media session, then we need to specify some >>>>>> alternative. >>>>>> >>>>>> Clearly there are at least two distinct cases here: >>>>>> >>>>>> - there is a desire to switch to a new address, but the >old address >>>>>> can continue to be supported until and unless use of >the new one >>>>>> can be established >>>>> [JRE] So if the contact address changes and we successfully >>>>> conclude the UPDATE transaction, and then the old contact address >>>>> disappears, it is likely that the Via list on the >re-INVITE request >>>>> will have become invalidated too, so the final response >will not reach the UAC. Correct? >>>>> >>>>> John >>>>> _______________________________________________ >>>>> Sipping mailing list >https://www.ietf.org/mailman/listinfo/sipping >>>>> This list is for NEW development of the application of SIP Use >>>>> sip-implementors@cs.columbia.edu for questions on current sip Use >>>>> sip@ietf.org for new developments of core SIP >>>>> >>>> >>>> _______________________________________________ >>>> Sipping mailing list https://www.ietf.org/mailman/listinfo/sipping >>>> This list is for NEW development of the application of SIP Use >>>> sip-implementors@cs.columbia.edu for questions on current sip Use >>>> sip@ietf.org for new developments of core SIP >>>> >>> >> >> >> >_______________________________________________ >Sipping mailing list https://www.ietf.org/mailman/listinfo/sipping >This list is for NEW development of the application of SIP Use >sip-implementors@cs.columbia.edu for questions on current sip Use >sip@ietf.org for new developments of core SIP > _______________________________________________ Sipping mailing list https://www.ietf.org/mailman/listinfo/sipping This list is for NEW development of the application of SIP Use sip-implementors@cs.columbia.edu for questions on current sip Use sip@ietf.org for new developments of core SIP
- [Sipping] Liaison Statement on offer/answer proce… Gonzalo Camarillo
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Elwell, John
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Gonzalo Camarillo
- Re: [Sipping] Liaison Statement on offer/answer p… Sanjay Sinha (sanjsinh)
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Sanjay Sinha (sanjsinh)
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Sanjay Sinha (sanjsinh)
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Ian Elz
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Sanjay Sinha (sanjsinh)
- Re: [Sipping] Liaison Statement on offer/answer p… Anders Kristensen
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… Gonzalo Camarillo
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- Re: [Sipping] Liaison Statement on offer/answer p… hannu.hietalahti
- Re: [Sipping] Liaison Statement on offer/answer p… Paul Kyzivat
- Re: [Sipping] Liaison Statement on offer/answer p… Christer Holmberg
- [Sipping] Current status of response to 3gpp Liai… Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … Rockson Li (zhengyli)
- Re: [Sipping] Current status of response to 3gpp … Christer Holmberg
- Re: [Sipping] Current status of response to 3gpp … Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … Rockson Li (zhengyli)
- Re: [Sipping] Current status of response to 3gpp … Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … Ian Elz
- Re: [Sipping] Current status of response to 3gpp … Christer Holmberg
- Re: [Sipping] Current status of response to 3gpp … Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … Christer Holmberg
- Re: [Sipping] Current status of response to 3gpp … Robert Sparks
- Re: [Sipping] Current status of response to 3gpp … DRAGE, Keith (Keith)
- Re: [Sipping] Current status of response to 3gpp … Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … DRAGE, Keith (Keith)
- Re: [Sipping] Current status of response to 3gpp … Paul Kyzivat
- Re: [Sipping] Current status of response to 3gpp … Robert Sparks