Re: [Sip] MUST 200 OK contain SDP? Thanks

Hi Yuantao
   I'm SunYongGuang, my msn is yongguangsun@hotmail.com

it is ok,

        "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. "
Does that mean if "Invite" contains SDP offer, "200 OK" MUST contain SDP
answer.
"the answer MUST be in a reliable non-failure message from UAS back to UAC
which is
  correlated to that INVITE" in your scenario  , the 180 with 100rel  is
reliable non-failure message and it includes SDP, the offer/answer is
completed, so the 200 response may include SDP or not, please refer RFC3262


2008/5/22, Yuantao Zhang <yuantao.zhang@ericsson.com>:
>
> Dear Sir or Madam
>
> I am an R&D engineer in Ericsson and really confused by the following
> part in RFC_3261. Could you please help us to explain it? Thank you very
> much.
> "
> 13.2.1 Creating the Initial INVITE
> .
> .
> .
>        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.
> .
> .
> ."
>
> Let's break it into 2 parts, in part 1,
>         "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. "
> Does that mean if "Invite" contains SDP offer, "200 OK" MUST contain SDP
> answer.
>
> In part 2,
>         "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."
> Does that mean if "Invite" contains SDP offer, the answer SDP MAY be in
> "180 ring" and not in "200 OK"? I think part 1 and part 2 are
> inconsistent.
>
> The attached sequence chart is the real problem we meet. Sx1 sends "bye"
> to sx2 after the "200 OK" because there is no SDP answer in "200 OK".
> But the producer of sx2 argues that the SDP answer is in "180 ring"
> already. No need to repeat it in "200 OK". Could you please tell me who
> is right? MUST 200 OK contain SDP? Thank you very much.
>
> Sx1                              xs2
>   ====1   invite(SDP)    ====>
> <====2   100 trying     ====
> <====3   180 ringing(SDP)====
>   ====4   prack          ====>
> <====5   200 ack        ====>
> <====6   200 OK (no SDP)====>
>
>
>
> Best Regards
> Yuantao Zhang
>
> I&V Engineer
> Broadband Networks R&D Center
> Ericsson (China) Company Ltd.
> Ericsson Tower          Phone :+86 10 8476 7240
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>
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