[Sipping] PRACK: Does an early-session SDP offer fullfills the rule to insert SDP in first reliable response (was: RE: PRACK: Does non-200 response cease re-transmission ofreliable 18x?)

["Christer Holmberg" <christer.holmberg at ericsson.com>]

Hi Paul, 

I've changed the subject, because I don't think this is related to the
re-transmission of 18x. It is a little related to the discussion about
relaxing the must-insert-SDP-in-first-reliable-18x, but let's still have
a separate thread for it.

> >  > >  > >>>Is the flows below valid according to recent arguments?
> >  > >  > >>>
> >  > >  > >>>   UAC                  UAS
> >  > >  > >>>    |----invite(SDP)--->|
> >  > >  > >>>    |<--- 183(SDP)------|
> >  > >  > >>>    |-----prack(SDP)--->|
> >  > >  > >>>    |<--- 200(SDP)------|
> >  > >  > >>>
> >  > >  > >>>       flow 1
> 
> >  > > 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.
> 
>The AS is an artifact of IMS, it has no role in any of the 
>ietf standards. It has been expected that components playing 
>various roles such as this are bound by normal distinctions 
>between UAC, UAS, Proxy, etc.
> 
>IMO it isn't a good idea to introduce a new kind of UA (or 
>proxy) that is bound by different rules.

I don't think a new role is proposed. The AS was just an example, but
from a SIP perspective it is of course behaving as a UAS in this case :)

>You might consider the "early-session" mechanism specified by RFC 3959.
>But I have never heard of it being implemented, so it may not be useful
to you.

I have been assuming that we ARE talking about the 3959 mechanism, and
the question has been whether an "early-session" SDP offer fullfills the
MUST rule to include SDP offer in the first reliable response.

IF we decide to relax the rule I guess it doesn't really matter, but if
we maintain the rule I guess it is a valid question.

Regards,

Christer