Subject: [sipcore] 答复: Re: New revision of the re-INVITE handling draft

From: [email-masked]
Date: Thu, 23 Jul 2009 21:39:37 +0800

Hi,

please see inlines.

Thanks

Gao

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Hi，

  It seems that clear definition of "legacy UAS" is necessary too.

[Gao] IMO，UAS not behaving as in the draft is "legacy UAS". For details, 
that is UAS sending non-2xx after O/A pair(s).
That's my understanding of "legacy UAS", but I am not sure it is the same 
as the original thought of Gonzalo. 

Also, if the UAC sends a re-INVITE with SDP that is "sendonly",
does the UAC have rules to determine whether the UAS use the new 
paramters, 
or not?

[Gao] As the Offer sent by UAC using "sendonly", the UAS would not use new 
paramters in send direction.
Then let's consider the recv direction:
By RFC3264, answerer should listen using both the *new* and *old* 
paramters until media using *new* paramters comes. So, when UAC get the 
answer, it can figure out that UAC has begun to recv media using *new* 
paramters.

Until here, things is under control of  RFC3264's definition. 

But I'd like to extend this case considering precondition.
Media modification in RFC3264 just has one O/A pair. And the answer is 
treated as accept of offer. But it is not the case while considering 
precondition: user of answerer only have the chance for decision of 
acceptance after precondition satisfied. Before precondition satisfied, 
there can be more than one O/A pairs. 

The offerer may wait answerer start to use *new* paramters fisrt, and take 
it as trigger. But as SDP is "sendonly", answerer would not send media to 
offerer. So, the proper trigger here can be 2xx of the Re-INVITE. And this 
is enhancement for RFC3264. I think it should be noted down.

I think it can be a separate text. 

"draft-camarillo-sipcore-reinvite-00" is aimed for correction of RFC3261. 
While what we talked now is correction of RFC3264. I think we can do it 
separately.

Regards,
Eric

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