Subject: [sipcore] About O/A rules in RFC3261:

From: [email-masked]
Date: Wed, 7 Apr 2010 11:39:18 +0800

Hi,

While considering one problem in our productions' interoperability 
testing, I re-read some parts of offeranswer draft and correlative part of 
RFC3261. And I find a potential description problem in RFC3261 
incidentally.

//correlative part of RFC3261
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.

As the text allow UAS send SDP before the final answer, the first session 
description UAC receives can not be treated as answer in such cases. And 
the current text defines that UAC MUST ignore any SDP in subsequent 
responses to the initial INVITE. whick may make the UAC ignore the real 
answer in some case.

I think the description should be: 
The UAC MUST treat the first session description which is in a reliable 
non-failure message it receives as the answer, and MUST ignore any session 
descriptions in subsequent responses to the initial INVITE.

And if the problem is exist, where should be the correction's location?
I think draft-ietf-sipcore-reinvite-03 is not proper, as it aims for 
Re-INVITE. And a new draft for such tiny *potential* problem is also not 
proper.

Thanks,

Gao

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