Hello,
I don't think this is something FS can do. Let me explain:
We have FS-A and FS-B, between which are multiple SIP providers. We are checking that the providers between A and B don't divert calls to non-approved vendors. So what I'm doing is:
When relaying the call from FS-A to the provider, I'm adding a SIP header with a unique ID, which is inserted into a DB table.
When FS-B receives the call, i retrieve the header ID and look it up in the table and mark it as answered.
On FS-A, when the call is answered, it looks up the ID and makes sure it has been marked as "answered" by FS-B.
If it is NOT marked, FS-A MUST disconnect the call.
I hope the explanation was clear, and if anyone has a better idea of how to do this, I'm all ears :)
Thanks
David