Hi,
I don't see any use case for this additional answer.
The text in chapter 13.2.1 says that the answer must be sent
in "A" (it
doesn't say "only one") reliable response. The
text also says that SDPs
in subsequent responses to the INVITE.
I DO agree life would be much easier if we from the
beginning would have
said that an answer MUST only be sent ONCE - without
"previews",
"re-sendings in additional responses" etc. But, no
matter what the
intention of chapter 13.2.1 was, it does cover the case when
additional
SDPs are received, so people just have to implement it
correctly...
Regards,
Christer
________________________________
From: prince.philip aricent.com
[mailto:prince.philiparicent.com]
Sent: 21. marraskuuta 2007 5:40
To: Christer Holmberg
Cc: Jonathan Rosenberg; Paul Kyzivat; Sanjay Sinha
(sanjsinh);
sip List
Subject: RE: [Sip] SIPit21: SDP in a 200OK when using
100rel
Since in the UAC point of view the behaviour is defined
clearly, whats the issue?
Does anybody see any use case for this additional answer,
from
an UAS perspective?
Prince.
-----"Christer Holmberg"
<christer.holmbergericsson.com> wrote:
-----
To: "Jonathan Rosenberg" <jdrosencisco.com>, "Paul
Kyzivat" <pkyzivatcisco.com>
From: "Christer Holmberg"
<christer.holmbergericsson.com>
Date: 11/21/2007 12:33AM
cc: "Sanjay Sinha (sanjsinh)" <sanjsinhcisco.com>,
sip List <sipietf.org>
Subject: RE: [Sip] SIPit21: SDP in a 200OK when using
100rel
Hi,
An implementation should keep offer/answer state and
simply discard the SDP in the 200 OK.
I don't think that is complicated 
Regards,
Christer
________________________________
From: Jonathan Rosenberg [mailto:jdrosencisco.com]
Sent: Tue 20/11/2007 17:56
To: Paul Kyzivat
Cc: Sanjay Sinha (sanjsinh); sip List
Subject: Re: [Sip] SIPit21: SDP in a 200OK when using
100rel
The intention was that, when reliable provisionals are
used, the answer
would NOT appear in the 200 OK to the original INVITE.
The paragraph in
RFC3261 is talking specifically about the case of an
unreliable
provisional response.
The drawback of sending the answer in the reliable 18x
and then
repeating it in the 200 OK, is what if they are not the
same. It gets
really complicated if there are multiple O/A exchanges
in UPDATE/PRACK
prior to the final 200 OK.
-Jonathan R.
Paul Kyzivat wrote:
>
>
> Robert Sparks wrote:
>> Yes, I did mean 200 INVITE.
>>
>> On Nov 19, 2007, at 3:22 PM, Sanjay Sinha
(sanjsinh)
wrote:
>>
>>> It is not clear from the call flow if the 200
OK is
for PRACK or INVITE?
>>>
>>> I guess you meant 200 OK for Invite. If that
is the
case, I think the
>>> RFC is clear that the answer sdp is optional
in it
and if it does have
>>> an answer sdp, it MUST be idential to answer
in 18x.
>>>
>>
>> Really? Point me to where you find this please.
>
> Mostly in 3261 sec 13.2.1. It says:
>
> 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.
>
> The first three sentences are the clearly normative
part. When combined
> with RFC 3262 definition of reliable provisionals,
they say that the
> reliable provisional contains the answer.
>
> The last sentence doesn't really say the UAS may
include sdp in
> subsequent responses to the invite transaction, but
neither does it say
> you can't. It does say the UAC should ignore them if
present, which
> implies they can be present, but says nothing about
what value they must
> have if they are present.
>
> AFAIK there is nothing that says the answer may be
repeated in the 200.
> However it is seemingly done a lot, so one had
better
beware.
>
> Paul
>
>>> But I think the
>>> offer-answer draft has clarified it further
that it
should not have any
>>> answer sdp. This is probably harsh in case of
one
offer-answer exchange,
>>> but makes sense if there are multiple early
dialog
offer-answer
>>> exchanges in say Prack/200 OK or using
UPDATE.
>
>
>
>>> Sanjay
>>>
>>>> -----Original Message-----
>>>> From: Robert Sparks [mailto:rjsparksnostrum.com]
>>>> Sent: Monday, November 19, 2007 4:14 PM
>>>> To: sip List
>>>> Subject: [Sip] SIPit21: SDP in a 200OK
when using
100rel
>>>>
>>>> There was a lot of discussion and
disagreement at
SIPit21
>>>> about whether the following 200 OK is
allowed (or
should) have
>>>> SDP in it:
>>>>
>>>> INVITE (offer)
>>>> -------->
>>>> 18x (with 100rel) (answer)
>>>> <--------
>>>> PRACK
>>>> --------->
>>>> 200 OK (can this carry SDP?)
>>>> <---------
>>>> ACK
>>>> --------->
>>>>
>>>> I couldn't find anything definitive in
RFC form.
Paul's
>>>> offeranswer draft talks about this I
think.
>>>>
>>>> If I understand things, the right answer
here is
that it's not
>>>> supposed to carry any SDP and that you
should
ignore it if it shows up.
>>>>
>>>> The question is, other than waste, what
can go
wrong if it is there?
>>>> When we end up with clear text around
the
requirement, will it
>>>> say SDP SHOULD NOT, or MUST NOT appear?
>>>>
>>>> Or do I have this wrong?
>>>>
>>>> RjS
>>>>
>>>>
>>>>
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>>
>>
>>
>> _______________________________________________
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>> This list is for NEW development of the core SIP
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>
>
> _______________________________________________
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