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Re: [Sipping] About offeranswer draft:




Hi Eric,

Are you ZTE's Eric? I have one colleague also named Eric wang(Wang Libo).

And some comments inlines.

Thanks,

Gao

sipping-bounces@xxxxxxxx 写于 2010-04-14 13:04:34:

> Hi all,

>  
>     I believe that SDP in non-reliable response is useful. eg, if
> the UAS wants to send a tone to UAC while the UAC doesn't support
> 100rel, the UAS can use a non-reliable response with the tone SDP.

> So I believe different SDPs(compare with the answer) can exist in
> non-reliable response and final 2xx response.


Yes, it is so in many deployed network. But the key problem here about the UAC's normative handling of the real answer, if it is different from the previous the SDP from the UAS.

>  
>    But, when I saw the chart below, the only words in my mind is
> ,"OMG, the SIP is never SI(m)P(le) again!"


I guess it is the extreme use case in theory. Considering normal call flow, it would be more simple. But if we should evaluate the rules, we usually need such use cases, as Shinji showed us.

>  
>
>
>  

> 2010/4/14 OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>
> Hi Gao,
>
> In the following case,
>
>      UAC                   UAS
>       | F1  INVITE (SDP1)   |  <-- offer
>       |-------------------->|
>       | F2     1xx (SDP2)   |
>       |<--------------------|
>       | F3     1xx (SDP3)   |
>       |<--------------------|
>       | F4 1xx-rel (SDP4)   |  <-- answer
>       |<--------------------|
>       | F5 1xx-rel (SDP5)   |
>       |<--------------------|
>       | F6    1xxl (SDP6)   |
>       |<--------------------|
>       | F7  2xx INV(SDP7)   |
>       |<--------------------|
>       | F8     ACK          |
>       |-------------------->|
>    (PRACK transactions are not shown)
>
> I tried to arrange the rules.
> (small letters mean informational)
>
> UAC,
> (Rc1)   MUST treat SDP2 as the answer.
> (Rc2)   MUST ignore SDP5, SDP6 and SDP7.
> (Rc3)   may treat SDP3 as the answer.
> (Rc4)   should treat SDP4 as the answer and confirm the current O/A
> status by sending new offer.
>
> UAS,
> (Rs1)   should not send SDP5, SDP6 and SDP7.
> (Rs2)   must not send SDP2 and SDP3 if these are not the same as SDP4.
>
> Rc3 and Rc4 are new added descriptions.
> Rs1 and Rs2 are current descriptions in this draft.
>
> I think "MUST NOT" is suitable for (Rs1).
> Because RFC3261 says
>        Once the UAS has sent or received an answer to the initial
>        offer, it MUST NOT generate subsequent offers in any responses
>        to the initial INVITE.  This means that a UAS based on this
>        specification alone can never generate subsequent offers until
>        completion of the initial transaction.
>
> SDP5 and SDP7 are regarded as "subsequent offers".
>
> What do you think of these?

>
> Regards,
> Shinji
>
> gao.yang2@xxxxxxxxxx

> Mon, 12 Apr 2010 11:37:09 +0800
> >Hi Shinji,
> >
> >Please see inlines.
> >
> >Thanks,
> >
> >Gao
> >
> >sipping-bounces@xxxxxxxx 写于 2010-04-12 10:55:47:
> >
> >> Hi Gao,
> >>
> >> The clarifications for the section 13.2.1 of RFC 3261 is
> >> one of the major purposes in this draft.
> >>
> >> In the section 3.1 of this draft,
> >> |   3.1.  Offer/Answer for the INVITE method with 100rel extension
> >> |   (snip)  All the session
> >> |   descriptions in the unreliable responses to the INVITE request must
> >> |   be identical to the answer which is included in the reliable
> >> |   response.
> >>
> >> Do you doubt this clarification?
> >> In my understanding, this has already reached the consensus in WG.
> >
> >[Gao] I am not want to *challenge* the consensus we have reached in WG.
> >But as this draft is aims for clarification, not for normative correction,
> >I have no way to convince the *UAS*.
> >
> >>
> >> I'm confused.
> >> Do you have something a concrete proposal?
> >
> >[Gao] I think the original illegibility is from RFC3261. So, I sended
> >mails about it in SIPCore ML:
> >
> >http://www.ietf.org/mail-archive/web/sipcore/current/msg02315.html
> >http://www.ietf.org/mail-archive/web/sipcore/current/msg02328.html
> >
> >To be honest, I think there are two options here:
> >1. Forbid different SDP(compare with the answer) before the answer
> >normatively.
> >2. Allowing different SDP(compare with the answer) before the answer
> >normatively.
> >
> >>
> >> Just to be sure, this draft is not a normative document but
> >> an informational one as you no doubt know.
> >
> >[Gao] Sure, I know it is informative.
> >
> >>
> >> Regards,
> >> Shinji
> >>
> >> gao.yang2@xxxxxxxxxx
> >> Fri, 9 Apr 2010 16:50:12 +0800
> >> >Hi Shinji,
> >> >
> >> >Thanks firstly.
> >> >
> >> >But the UAS do not think it throws the problem. RFC3261 said UAS may send
> >> >the same SDP before the answer, but there is not normative words of to
> >> >forbid the different SDPs.
> >> >
> >> >And if the equipment has been in the network, unless we using the evident
> >> >standard, we has no way to request their correction.
> >> >
> >> >Gao
> >> >
> >> >OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>
> >> >发件人:  sipping-bounces@xxxxxxxx
> >> >2010-04-09 16:30
> >> >
> >> >收件人
> >> >sipping@xxxxxxxx
> >> >抄送
> >> >
> >> >主题
> >> >Re: [Sipping] About offeranswer draft:
> >> >
> >> >Hi Gao,
> >> >
> >> >In this case it is no doubt the UAS is a cause of the problem.
> >> >All you have to do is say "Your UAS is against the rules".
> >> >You will surely win the fight.
> >> >
> >> >Regards,
> >> >Shinji
> >> >
> >> >gao.yang2@xxxxxxxxxx
> >> >Fri, 9 Apr 2010 15:25:58 +0800
> >> >>Hi Shinji,
> >> >>
> >> >>By myself, I am OK with the three ways. But if there's no normative
> >> >>definition here, there would be some interworking fight for this issue.
> >> >>
> >> >>Thanks,
> >> >>
> >> >>Gao
> >> >>
> >> >>OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>
> >> >>发件人:  sipping-bounces@xxxxxxxx
> >> >>2010-04-09 14:23
> >> >>
> >> >>收件人
> >> >>sipping@xxxxxxxx
> >> >>抄送
> >> >>
> >> >>主题
> >> >>Re: [Sipping] About offeranswer draft:
> >> >>
> >> >>Hi Gao,
> >> >>
> >> >>Considering a BCP recommendation in this case,
> >> >>
> >> >>>When UAC receives the different SDP in a reliable response from
> >> >>>the prior one in a non-reliable response, UAC may ...
> >> >>>1. terminate the session.
> >> >>>2. keep using the SDP in a non-reliable response.
> >> >>>3. change to the SDP in a reliable response.
> >> >>
> >> >>and,
> >> >>4. In case 2 or 3, it is recommended that the UAC confirms the current
> >> >>   offer-answer status using a reINVITE or an UPDATE request.
> >> >>
> >> >>However I think "may" is adequate in case 3.
> >> >>
> >> >>Regards,
> >> >>Shinji
> >> >>
> >> >>gao.yang2@xxxxxxxxxx
> >> >>Fri, 9 Apr 2010 11:44:34 +0800
> >> >>>Hi,
> >> >>>
> >> >>>Yes, considering implementation, I also find the three ways, especially
> >> >>>for the last two ways.
> >> >>>
> >> >>>My original thought is make clarification on the third one("3.change to
> >> >>>the SDP in a reliable response"), by RFC3264's rule.
> >> >>>
> >> >>>In fact, I think by rules, the UAC should modify the session
> as it is the
> >> >>>lawful answer. Using early media by the SDP prior to the
> lawful answer is
> >> >>>something outside of the lawful rules(Reliably way of using
> earlymedia is
> >> >>>Answer in 100rel).
> >> >>>
> >> >>>So, I think using or just discarding the SDP prior to the
> lawful answer is
> >> >>>something depends on implementation. While "change to the SDP in a
> >> >>>reliable response" should be normative.
> >> >>>
> >> >>>Thanks,
> >> >>>
> >> >>>Gao
> >> >>>
> >> >>>OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>
> >> >>>发件人:  sipping-bounces@xxxxxxxx
> >> >>>2010-04-09 10:13
> >> >>>
> >> >>>收件人
> >> >>>sipping@xxxxxxxx
> >> >>>抄送
> >> >>>
> >> >>>主题
> >> >>>Re: [Sipping] About offeranswer draft:
> >> >>>
> >> >>>Hi Gao,
> >> >>>
> >> >>>I have no doubt that the different SDP in non-reliable response
> >> >>>violates current regulations.
> >> >>>
> >> >>>The behaviour of UAC is an implementation issue, I think.
> >> >>>When UAS receives the different SDP in a reliable response from
> >> >>>the prior one in a non-reliable response, UAS may ...
> >> >>>1. terminate the session.
> >> >>>2. keep using the SDP in a non-reliable response.
> >> >>>3. change to the SDP in a reliable response.
> >> >>>
> >> >>>It is not clear, but it is not a regular case.
> >> >>>
> >> >>>Regards,
> >> >>>Shinji
> >> >>>
> >> >>>gao.yang2@xxxxxxxxxx
> >> >>>Wed, 7 Apr 2010 11:14:07 +0800
> >> >>>>Hi Paul,
> >> >>>>
> >> >>>>While considering one problem in our production's interoperability
> >> >>>>testing, I re-read some parts of offeranswer draft and find something
> >> >>>>might be deserving discussion.
> >> >>>>
> >> >>>>//begin of text(part):
> >> >>>>   For example, in Figure 1, only the SDP in F6 is the answer.  The SDP
> >> >>>>   in the non-reliable response (F2) is the preview of the answer and
> >> >>>>   must be the same as the answer in F6.  Receiving F2, the UAC should
> >> >>>>   act as if it receives the answer.
> >> >>>>//end of text(part)
> >> >>>>
> >> >>>>[Gao] In fact, UAS sending SDP in non-reliable response is
> for potential
> >> >>>>early media usage. Considering some UAS may have different address for
> >> >>>>early media channel and the final session, some UAS may send different
> >> >>>>SDP(compare with the answer) in non-reliable response. And I
> really found
> >> >>>>such equipment inside and outside of ZTE. And considering
> UAC, Ithink we
> >> >>>>should allow the UAC ignore the SDP in non-reliable response,while some
> >> >>>>UAC really do not handle any SDP which is not offer or answer.
> >> >>>>
> >> >>>>But the permissibility of the degree of the difference might
> be delicate.
> >> >>>>If the non-answer SDP just has different ip address or port,
> it seams OK.
> >> >>>>If the non-answer SDP has different media streams, it would be hard to
> >> >>>>handle for UAC.
> >> >>>>
> >> >>>>
> >> >>>>And I re-read correlative part of RFC3261. I don't know that whether
> >> >>>>allowing different SDP(compare with the answer) in non-
> reliable response
> >> >>>>is violation/correction of current text or not.
> >> >>>>
> >> >>>>//correlative part of 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.
> >> >>>>
> >> >>>>Thanks,
> >> >>>>
> >> >>>>Gao
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