http://cabernet.levkowetz.com/html/draft-ietf-sipping-sip-offeranswer-11
3.1.1. INVITE Request with SDP
When a UAC includes an SDP body in the INVITE request as an offer, it
expects the answer to be received with one of the reliable responses.
Other than that, no offer/answer exchanges can occur in the messages
within the INVITE transaction.
UAC UAS
| F1 INVITE (SDP) | <- The offer in the offer/answer model
|-------------------->|
| F2 1xx (SDP) | <- The offer/answer exchange is not
|<--------------------| closed yet, but UAC acts as if it
| | ^ receives the answer.
| F3 1xx-rel (no SDP) | |<- a 1xx-rel may be sent without answer
|<--------------------| | SDP.
| F4 PRACK (no SDP) | |
|-------------------->| | UAC must not send a new offer.
| F5 2xx PRA (no SDP) | |
|<--------------------| v
| |
| F6 1xx-rel (SDP) | <- The answer in the offer/ answer model
|<--------------------| -
| F7 PRACK | | UAC can send a new offer in a PRACK
|-------------------->| | request to acknowledge F6.
| F8 2xx PRA | | After F7 UAC and UAS can send a new
|<--------------------| v offer in an UPDATE request.
| |
| F9 1xx-rel | <- SDP should not be included in the
|<--------------------| subsequent 1xx-rel once offer/answer
| F10 PRACK | has been completed.
|-------------------->|
| F11 2xx PRA |
|<--------------------|
| |
| F12 2xx INV | <- SDP should not be included in the
|<--------------------| final response once offer/answer has
| F13 ACK | been completed.
|-------------------->|
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Attila
Sipos
Sent: 11 February 2010 14:53
To: Iñaki Baz Castillo; [email protected]
Subject: Re: [Sip-implementors] About SDPs received in provisional responses
>>Anyhow, even when using 100rel I "think" (not 100% sure) that the SDP
>>must be included in the 200 OK even if it's just a copy of the SDP in
>>a previous provisional response. Hope somebody else could confirm
>>this.
Strictly, once the 180 has been PRACKed, the 200 OK must not have SDP.
IIRC, there are some scenarios (which I cannot think of right now) where
putting the 200 OK in both 180 (w/PRACK) and 200 causes problems.
(I think the problem scenarios are forking scenarios or UPDATE scenarios)
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Iñaki Baz
Castillo
Sent: 11 February 2010 14:45
To: [email protected]
Subject: Re: [Sip-implementors] About SDPs received in provisional responses
El Jueves, 11 de Febrero de 2010, Saúl Ibarra escribió:
> Hi all,
>
> Today I noticed some behavior in a UA that looked weird to me and as I
> couldn't find an explanation on the RFC, hope someone can help me :)
>
> This UA *only* sends the SDP in the 180 provisional response, the 200
> OK doesn't contain an SDP, and no PRACK is being used. So my question
> is if this valid according to the RFC?, also if you could point me to
> the place in which is explained I'd really appreciate it.
The point here is that the SDP cannot change after a first one has been
included by the UAS within a provisional response. If the SDP changes in a new
provisional response or a final 200 then such SDP must be ignored (the SDP
cannot change within the same early-dialog).
However, a UAS should include the SDP in the 200 since the provisional response
is not reliable (as you said there is not 100rel requeriment so the UAS accepts
an INVITE without "100rel" in Require/Supported header). So the UAS cannot know
if the provisional response has been received or not by the UAC.
Anyhow, even when using 100rel I "think" (not 100% sure) that the SDP must be
included in the 200 OK even if it's just a copy of the SDP in a previous
provisional response. Hope somebody else could confirm this.
--
Iñaki Baz Castillo <[email protected]>
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