To Paul
Yes.
But there has been the emergence of the practical problem while interworking of equipment from different corporation.
To solve the call forwarding problem, we has two base choice: Forking and no Forking.
Currently, TISPAN using no Forking way(in fact, B2BUA way).
Then, if 3GPP want to using Forking way to replace the current no Forking way, it should rewrite "3GPP TS 24.404".
Or if 3GPP want to along the no Forking way, then it should resolve the interworking problem arosed by "INVITE with/without SDP problem".
Thanks
Gao
To Christer
As you are the rustler of 3GPP, can you talk about this topic too.
Thanks
Gao
Paul Kyzivat <pkyzivat@xxxxxxxxx> 写于 2009-04-10 12:59:59:
>
>
> gao.yang2@xxxxxxxxxx wrote:
> >
> > Hi,
> >
> > Thanks for your answer.
> >
> > Using forking, Offer/Answer would be in two different dialogs. So, it
> > has no such problem. But the TISPAN's standard using B2BUA mode for Call
> > Forwarding.
>
> Oh. Then the game may be different.
>
> > As:
> >
> > if A-C's negotiate still in the original dialog(having done A-B's
> > negotiate), then it is B2BUA mode:
> >
> > 1. if the INVITE to C has Offer, there would be using C's Answer as
> > Offer send to A, usually using UPDATE.
> >
> >
> > |---->Offer(1)
> > |<----Answer(2)
> > Offer(3) <----|
> > Answer(4) ---->|
> >
> > Then we would have to judge whether the Answer(4) should be intercept or
> > transfer. If it should be transfered, then its the begin of next loop as
> > the current one.
> >
> > 2. if the INVITE to C has no Offer, then C's Offer would has different
> > stream as A's original desire. It is also a well known problem.
> >
> >
> > So. I want to know how you considering the problems. Thanks.
>
> I think it is very difficult to make this work. There are often
> problems, even without preconditions. Preconditions don't make it any
> simpler.
>
> IMO the answer is: if it hurts, don't do it.
> Even if the AS wants to act as a B2BUA, the AS can still establish
> multiple dialogs back to A, so the issue of sorting this out is left to
> A. Unless you are trying to deal with UAs that are unable to do that.
>
> Unless the B2BUA also terminates the media it may be impossible to
> resolve all the problems.
>
> Paul
>
> > Gao
> >
> >
> >
> >
> > *Paul Kyzivat <pkyzivat@xxxxxxxxx>*
> >
> > 2009-04-09 21:32
> >
> >
> > 收件人
> > gao.yang2@xxxxxxxxxx
> > 抄送
> > sipping@xxxxxxxx
> > 主题
> > Re: [Sipping] Question about Call Forwarding Busy(CFB)
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > gao.yang2@xxxxxxxxxx wrote:
> > >
> > > Use case: A call B(Busy), AS forward the call to C.
> > >
> > > By TISPAN standard(current 3GPP 24.404), AS would send INVITE to C. And
> > > this INVITE contain A's initial Offer.
> > >
> > > But if considering precondition, B would has Offer/Answer with A.
> > > Now, should the INVITE(by AS) contain A's initial Offer or not? Or is
> > > there standard define it?
> >
> > Are you assuming that the AS is acting as a proxy? Or as a B2BUA?
> >
> > Assuming its a proxy:
> >
> > If B is busy, then I would expect that there was no answer from B.
> > Rather just an immediate 486 response. This would never reach A and so
> > there is no issue.
> >
> > If for some reason B did send an answer in a provisional response before
> > signaling busy, then that would establish an early dialog with to-tag B.
> > Then later there will be a 486 response, intercepted by the AS, and not
> > forwarded to A.
> >
> > And then a copy of the original INVITE will be sent by the AS to C. When
> > C responds with an answer, it will be with to-tag C. Hence A will see
> > this as a new early (or final) dialog.
> >
> > A must negotiate the preconditions independently in the two dialogs.
> >
> > Thanks,
> > Paul
> >
> >
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