Re: Question about Call Forwarding Busy(CFB)

[email protected] 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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