OK. Then I guess TISPAN will have to figure out how
to deal with the
difficulties that their choices bring.
Thanks,
Palu
gao.yang2 at zte.com.cn wrote:
>
> 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 at cisco.com> 写于 2009-04-10 12:59:59:
>
> >
> >
> > gao.yang2 at zte.com.cn 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 at cisco.com>*
> > >
> > > 2009-04-09 21:32
> > >
> > >
> > > 收件人
> > > gao.yang2 at zte.com.cn
> > > 抄送
> > > sipping at ietf.org
> > > 主题
> > > Re: [Sipping] Question about Call Forwarding
Busy(CFB)
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > gao.yang2 at zte.com.cn 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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