What is False Answering Supervision?

Voice over Internet Protocol service has become very popular since the last two decades, but is vulnerable to many types of fraudulent activities. False Answering Supervision or FAS is one of the well known VoIP fraud of incorrectly extra billing the customers.

What is FAS?

To explain FAS simply, it is the scenario when after making a call, the caller gets billed also for the time the call is not answered. There are three main types of FAS.

The carrier returns the answer signal when ringing starts, rather than when the customer answers. This increases the duration of the call, and therefore the cost of the call. A call may even be charged despite being dropped due to no answer.
The more clearly fraudulent variant of this scheme involves call diversion. The fraudulent carrier will route the call to a recorded message that plays a ringing tone and then a recording . This is intended to keep the calling customer on the line and paying for the call as long as possible.
The call is not terminated when the recipient hangs up, and waits for the caller to disconnect. During the period between the recipient disconnecting and the caller disconnecting, the caller is billed.

How to identify FAS?

If the customer notices any of the the following, then it is pretty obvious that there is FAS problem.

The billing time is longer than the time for which the called party was available on the line.
The call is billed even if the called party is out of the coverage area.
The call is billed even if the called party is not available and the caller gets a voice mail.

Why FAS occurs?

FAS generally takes place if no synchronization is there between the VoIP leg and the PSTN leg of a call on a VoIP-to-PSTN gateway. When the call reaches the gateway from the VoIP network, the gateway tries to establish a connection with the called number, but due to incorrect configuration it cannot detect the states of the call, which are advertised by the PSTN network (the states are: "called party ringing", "called party connected"). And thus the gateway forces the "CONNECT" state and it normally happens immediately after the arrival of the call from the VoIP network or a few seconds after that. But the main idea is that the gateway connects the calls (which means starts the part of the call, which is billed) according to its own settings, but not according to the actual state of the call.

How FAS works?

The FAS server is placed into the routing of the switch. Now the calls that come to the FAS server will be forwarded to an IVR message, related to the dialed number. The message that will be played back will sound something like this: "the subscriber is out of reach, please, try to call later" (it depends on what message is recorded on the FAS server) but this message should be exactly the same as the caller would get from the real carrier of called number. The call will be billed from the very beginning and this will be the billable time that will generate additional profit.