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.
- 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.
Thanks,
Paul
Christer Holmberg wrote:
Hi,
Before sending an answer,
- An UAS MAY send unreliable provisional responses with a SDP.
- And the SDP MUST be identical to an answer SDP.
After sending an answer,
- The UAS should not insert a SDP in any response.
Is this OK?
That text still doesn't say what an SDP inserted after sending the
answer means, only that it should not be sent.
The SDP means nothing. it is neither an offer nor an answer.
Exactly. In my opinion that is what is important - not whether the UAS inserts SDP or not.
I still don't see why we need to make a separation about SDP sent
before and after the answer, because in both cases the SDP must be
identical to the answer.
1. RFC3261 says that UAS MAY send it before the answer and
doesn't say nothing after the answer.
That is one reason why we are writing the draft - to clarify things which may not be clear in the specs.
2. The SDP MUST be ignored by UAC. it is meaningless.
I agree, and that is what we must be clear about. Because, as we know, some people want to send a NEW offer (or updated answer) in a subsequent response, and that is not allowed.
3. if another o/a exchange is occured (using UPDATE or PRACK), it is not even a confirmation.
And, again, I know there are many implementations that send
a copy of the SDP after the SDP answer has been sent, so instead of
saying that it should not be done I think it is much more important to
say that, if it is done, it must be identical to the SDP answer. In other
words, to make it clear that the UAS can not send a NEW offer (or
updated answer) in a subsequent response after the SDP answer has been sent.
Since UAC MUST ignored it, there is no problem on a interworking.
Why must it be identical to the SDP answer?
Well, if you look at it that way, fine. But, then the important thing is that the UAC must ignore it - not that the UAS should not send it.
Regards,
Christer
Regards,
Christer
Hans Erik van Elburg <ietf.hanserik@xxxxxxxxx> Mon, 19 Apr 2010
13:55:41 +0200
- An UAS MAY insert a SDP body that is identical to the
SDP answer,
in an unreliable provisional response before the SDP answer has
been sent.
- The UAS MUST NOT insert a SDP body that is not
identical to the
SDP answer, in an unreliable provisional response before the SDP
answer has been sent.
This is terribly confusing. Very probabe that noone will
get it right.
Triple negation. And talking about sending and answer before the
answer has been sent. ???
- The UAS MUST NOT insert a SDP body in any response
after the SDP
answer has been sent.
This means that you can't send it again after you've send it in an
unreliable provisional response. Do you want tto say that?
/Hans Erik van Elburg
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