Hi Shinji,
sipping-bounces@xxxxxxxx 写于 2010-04-14 15:31:54:
> Hi Gao,
>
> gao.yang2@xxxxxxxxxx
> Wed, 14 Apr 2010 12:21:45 +0800
> >sipping-bounces@xxxxxxxx 写于 2010-04-14 11:17:23:
> >
> >> 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.
> >
> >[Gao] OK
> >
> >> (Rc4) should treat SDP4 as the answer and confirm the current O/A
> >> status by sending new offer.
> >
> >[Gao] support of this, though this may be modification of current RFC3261.
>
> You will probably think of the following statements,
> RFC3261/13.2.1 Creating the Initial INVITE
> (snip) "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."
>
> No doubt this is one of the cussword built in this document.
> It is a personal interpretation of mine,
> "as the answer" is associated with not "treat" but "receives",
> and "treat" means "not ignore".
>
> Just putting that aside for now, I think there is a consensus that
> Rc4 does not need a modification of current RFC3261.
I see. But if there's memo of such consensus, it would be quite useful in interworking testing.
>
> >> 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.
> >>
> >
> >[Gao] Yes.
> >
> >> SDP5 and SDP7 are regarded as "subsequent offers".
> >
> >[Gao] as "MUST NOT" is suitable for (Rs1), so there must be no "subsequent
> >offers" in subsequent response.
>
> Certainly UAC MUST ignore SDPs no matter what these are.
>
> Regards,
> Shinji
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