Fighting against FAS

FAS (Fake Answer Start) - indication to caller about call answering, while dialed subscriber hasn't actually picked up the phone.
This is one of fraud schemes, often used in contemporary world of telecommunication.

This fraud is performed by telephony providers.
They indicate that call is answered and start billing while:
  • the outbound call towards dialed subscriber is in progress (call is directed to subscriber, but he hasn't picked up yet)
  • the outbound call towards dialed subscriber is not yet dialed (but will be dialed a bit later)
  • the call is not directed to dialed subscriber at all (audio file or ring-back tone is played back, or call is directed to call-center, where the task of operators is to hold a caller as long as possible)

This gives a chance to such a provider to send you overrated invoices.
During this kind of fraud it's obvious that caller suffers the most.
Unscrupulous providers could insert such FAS calls inside a call stream randomly.
Thus, it's hard to detect such calls.

To fight against FAS following methods are used:

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