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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