答复: Re: Question about Call Forwarding Busy(CFB)
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.
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.
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.
|Paul Kyzivat <pkyzivat@xxxxxxxxx>
|Re: [Sipping] Question about Call Forwarding
> 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.
> 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
> 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.
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