On 4/20/2010 7:04 AM, Paul Kyzivat wrote:
DRAGE, Keith (Keith) wrote:
Do remember that there are certain cases where the UAC will not ignore
it. These are the cases where the message containing original answer
has not yet arrived or been lost, and the protocol has not yet
recovered from that.
Hmm. Can you say more?
Are you thinking of a case where the answer has been sent in a reliable
provisional, but the PRACK has not yet been received? And then that
*some* SDP is included in a subsequent unreliable provisional, or 2xx?
That is an interesting case. The one that would be least wierd is:
UAC UAS
| INVITE (SDP1) |
|----------------->|
| 1xx REL (SDP2) |
| X--------------|
| 2xx (no SDP) |
|<-----------------|
This is not a valid case. It's explicitly ruled out by 3262:
If the UAS had placed a session description in any reliable
provisional response that is unacknowledged when the INVITE is
accepted, the UAS MUST delay sending the 2xx until the provisional
response is acknowledged. Otherwise, the reliability of the 1xx
cannot be guaranteed, and reliability is needed for proper operation
of the offer/answer exchange.
Thanks,
Anders
I think that implies a different best practice:
If the UAS has sent an answer in a reliable provisional, if it sends a
2xx before receiving a prack of the answer, it should include the answer
in the 2xx as well.
(If the UAS intends to initiate another o/a it MUST await the prack, so
if the 1xx is lost it will be retransmitted.)
Thanks,
Paul
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regards
Keith
-----Original Message-----
From: sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] On
Behalf Of Christer Holmberg
Sent: Tuesday, April 20, 2010 1:47 PM
To: OKUMURA Shinji; sipping@xxxxxxxx
Subject: Re: [Sipping] Is SDP in an unreliable response "the answer" ???
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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This list is for NEW development of the application of SIP
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This list is for NEW development of the application of SIP
Use sip-implementors@xxxxxxxxxxxxxxx for questions on current sip
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