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Re: [Sipping] 答复: RE: PRACK: Does non-200 response cease re-transmission ofreliable 18x?

wang.libo at zte.com.cn wrote:


Hi,

 >
 > >>>Is the flows below valid according to recent arguments?
 > >>>
 > >>>   UAC                  UAS
 > >>>    |----invite(SDP)--->|
 > >>>    |<--- 183(SDP)------|
 > >>>    |-----prack(SDP)--->|
 > >>>    |<--- 200(SDP)------|
 > >>>
 > >>>       flow 1
> >>> > >>Assuming the 200 is the PRACK response, yes. > >>> > >>> UAC UAS 
 > >>>    |----invite-------->|
 > >>>    |<--- 183-----------|
 > >>>    |-----prack(SDP)--->|
 > >>>    |<--- 200(SDP)------|
> >>> > >>> flow 2 > >>> > >>Not valid. If the INVITE does not contain SDP, a reliable answer must 
 > >>contain SDP. We are currently discussing whether the FIRST reliable
 > >>response must contain SDP, or whether that rule can be related. But,
 > >>that is a separate thread.
 > >
 > >Hmm. That flow is a consequence of changing that rule that I had not
 > previously considered.
 > >
 > >Allowing flow 2 would cause all sorts of trouble. If the restriction on
 > offer in first reliable provisional is to be
 > >relaxed it must be sure to state that the first offer must then be in
 > *some* reliable provisional, and until that is sent
 > >there can be no offer sent another way (PRACK or UPDATE).
 > >
 > >Just opening that question is enough to make me more concerned about
 > relaxing the constraint.
 >
 > I am not proposing to allow flow 2, and I don't think relaxing the rule
 > would allow it either. The rule would say that if the INVITE does not
 > contain an SDP offer the SDP offer must be carried in a reliable
 > response. The PRACK can only contain an SDP offer if the UAC has receied
 > an SDP answer.

Does it means,the first flow is allowed?


Yes.
I think, the restriction the first reliable response must contain SDP if the INVITE without SDP 
should restrict the called user.


That's the way it is now.
It seems there is a exception about H.323, but i know nothing about the case at this moment, does
There is currently no such exception. There is some discussion underway regarding possibly making one. H.323 behavior is one justification.
the unreliable response or delaying to send the first reliable response solve the H.323 case? 

delaying does.

	Paul


Regards,
Eric


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