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

[Paul Kyzivat <pkyzivat at cisco.com>]

wang.libo at zte.com.cn wrote:

>  > >  > >>>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.

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.

	Thanks,
	Paul