Re: [Sipping] Is SDP in an unreliable response "the answer" ???

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Hi,

>>>Yes. As Paul's conclusion of BCP, UAS should not include SDP after sending the ANSWER.
>>>
>>>My talking is , even UAS violate the BCP suggestion, there's no normative problem.
>>
>>Exactly.
>>
>>So, the important thing is to make clear, that IF the UAS sends SDP after sending the answer, it CAN NOT send a new offer.
>
>There is a subtlety here. What you say is correct: the UAS *can not*
>send a new offer, which is stronger than saying it *may not*. It matters
>not whether it *thinks* it is sending an offer - it never will be an offer.

Correct. That's why "can not" is also better than "must not", since it is by definition not even technically possible to send a new offer.

Regards,

Christer




>       Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>
>
>       2010-04-21 19:44
>
>
>               收件人
>               "gao.yang2@xxxxxxxxxx" <gao.yang2@xxxxxxxxxx>
>               抄送
>               OKUMURA Shinji <shinji.okumura@xxxxxxxxxxxx>, "sipping@xxxxxxxx" <sipping@xxxxxxxx>, "sipping-bounces@xxxxxxxx" <sipping-bounces@xxxxxxxx>
>               主题
>               RE: [Sipping] Is SDP in an unreliable response "the answer" ???
>
>
>
>
>
>
>
>       Hi,
>
>       >> I don't disagree with what people are saying, but trying to read it
>       >> from a I-am-a-new-implementor-and-I-would-like-to-get-it-right-from-
>       >> the-beginning perspective I don't think anything is clarified. Eg.
>       >> talking about that an SDP sent after the answer would be
>       >> "missunderstood as a new offer" is confusing.
>       >
>       >                 I guess "missunderstood as a new offer" issue is clear:
>       >                 If the session-id of o= line is the same the ANSWER, UAC can treate it as just COPY of the answer;
>       >                 If the session-id is higher than the ANSWER's session-id, the UAC can treate it as *new* offer. As the UAC MUST ignore any SDP after ANSWER, it is OK for UAC doing nothing. But if UAC checks the SDP and find it is
>       >                 *new* offer and violation of O/A rules then terminate the session, I also think it is also OK(UAS do bad behavior at first).
>
>       I am not talking about the UAC procedure. I fully support saying that the UAC ignores the SDP.
>
>       My problem is to say that the UAS shall not include SDP, because the UAC could "missunderstand it as a new offer". All we need to say is that the UAS MUST NOT include a new SDP.
>
>       Regards,
>
>       Christer
>
>
>
>
>
>
>
>
>
>
>
>
>
>                       > > -----Original Message-----
>                       > > From: sipping-bounces@xxxxxxxx
>                       > > [mailto:sipping-bounces@xxxxxxxx] On Behalf Of OKUMURA Shinji
>                       > > Sent: 21. huhtikuuta 2010 8:45
>                       > > To: sipping@xxxxxxxx
>                       > > Subject: Re: [Sipping] Is SDP in an unreliable response "the
>                       > > answer" ???
>                       > >
>                       > > Hi,
>                       > >
>                       > > Hans Erik van Elburg <ietf.hanserik@xxxxxxxxx> Tue, 20 Apr
>                       > > 2010 21:53:17 +0200
>                       > > >On Tue, Apr 20, 2010 at 3:47 PM, Paul Kyzivat
>                       > > <pkyzivat@xxxxxxxxx> wrote:
>                       > > >> Here is my attempt at summarizing the discussion conclusions:
>                       > > >>
>                       > > >> Normative things (stated or implied in existing RFCs):
>                       > > >>
>                       > > >> - If the UAC sent an offer in the INVITE, then after it
>                       > > receives SDP
>                       > > >> (the
>                       > > >> answer) in a reliable response to the INVITE, any SDP in
>                       > > subsequent
>                       > > >> responses to the INVITE MUST be ignored.
>                       > > >>
>                       > > >> - Further, if SDP is received in an unreliable response to
>                       > > the invite
>                       > > >> prior to receiving SDP in a reliable response, then it MUST be
>                       > > >> treated as the answer for purposes of media processing,
>                       > > but not for
>                       > > >> purposes of determining when another offer may be sent or received.
>                       > > >>
>                       > > >[HE] I miss what the UAC should do in this case for subsequent
>                       > > >responses, does the following hold as well:
>                       > > >"If the UAC sent an offer in the INVITE, then after it receives SDP
>                       > > >(the answer) in an unreliable response to the INVITE, any SDP in
>                       > > >subsequent responses to the INVITE MUST be ignored/granted/... ." ?
>                       > >
>                       > > I agree. And it's certainly "ignored".
>                       > >
>                       > > >Regardless what the correct behaviour is, it is missing in
>                       > > your summary.
>                       > > >
>                       > > >> - if the UAS receives an offer in the INVITE, it MUST NOT
>                       > > include SDP
>                       > > >> in any response it sends until it has determined the
>                       > > intended answer
>                       > > >> SDP to the offer.
>                       > > >>
>                       > > >> - once the intended answer SDP is determined, it MUST be sent in a
>                       > > >> reliable response to the INVITE. It MAY be sent in one or more
>                       > > >> *preceding* unreliable provisional responses.
>                       > > >>
>                       > > >> Non-normative, best practice suggestions:
>                       > > >>
>                       > > >> - if the UAS receives an offer in the invite, once it has sent the
>                       > > >> answer in a reliable response, it should not send any SDP in
>                       > > >> subsequent responses to the INVITE.
>                       > > _______________________________________________
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_______________________________________________
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This list is for NEW development of the application of SIP
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