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

[wang.libo at zte.com.cn]

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.


Sure, I means, the first reliable response from the
called user must contain 
NORMAL SESSION SDP in order to communication,but AS(application
server) 
shouldn't be restricted by this rule as AS may only
concern about early-session 
for pronunciation. Or, the AS is also restricted if
early-session plays the same
role as normal session.

Regards,
Eric


> 
> > 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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