Fake False Answer Supervision (FAS) service

The service described below is what most would consider fraud and is illegal in many countries.
The information is presented only to assist in identifying this type of fraud.

Fake FAS service is a service that allows you to earn extra money by mixing fake FAS calls into your real traffic. The service generates the needed carrier service messages and creates the needed billable airtime of your traffic, thus, simulating calls to numbers that are "out of coverage" and providing false billing.

FAS is commonly referred to as False Answer Supervision and for a regular user this phenomenon means incorrect extra billing of calls: the billing starts earlier than the called party actually picks up the phone.
What is Fake FAS service?
Fake FAS service is a service that simulates calls to numbers that are out of network coverage and that provides false billable airtime to the calling party. The service pretends to be a real mobile carrier and plays back real mobile carrier service messages (e.g. "the number you are calling is not reachable at the moment, please, call back later") while charging for this.

Once you notice one of the following, you are sure to experience a FAS problem :

- the billing of the call starts earlier than the called party picks up the phone

- the call is billed even if the called party is said to be out of the coverage (for example, for a mobile phone you get an announcement "we are sorry, but the party you are calling is unavailable at the moment")

- the call is billed even if the caller gets to a voicemail.

FAS normally takes place when there is no synchronization between a VoIP leg and PSTN leg of the 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.

FAS is considered to be a negative phenomenon due to two reasons:

1. The calling enduser may notice that he/she is billed for non-connected calls

2. FAS creates a bigger number of short duration calls (in a situation when there is no answer from the called party, the connected duration of the call is very short (as long as the calling party is willing to listen to Ring Back Tones without being answered), which brings down the ACD/ALOC (average call duration / average length of call) (due to a bigger than usual number of short calls) and brings up the ASR (average success rate) (due to a bigger than usual number of connected calls).

Normally this is a prerogative of the owners of the gateways that connect the VoIP network to PSTN network. The extra penny is earned by charging the calling party a bit more for the calls using the ability to control the "CONNECT" state of the call. But wholesale transit carriers can also take advantage of using FAS phenomenon to increase profit: by using our service it is possible to mix the needed percent of FAS calls into your existing traffic. This will slightly degrade the ACD parameter of your traffic, increase the ASR parameter and will allow you to earn extra money out of almost nowhere.

You put the FAS server into routing on your switch. 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 you are calling is out of reach, please, try to call later". (IMPORTANT NOTE: it is your responsibility to record such a voice message and to upload it to FAS server.) The message should be exactly the same as the caller would get from the real carrier, to whom this dialed number belongs. The call will be billed from the very beginning and this will be the billable time that will generate additional profit. The number of calls that would receive the fake FAS can be controlled either on your end (you would limit the number of calls sent to FAS server) or on the FAS server side (it would control the number of calls that will receive fake FAS and will reject the rest of the calls without forwarding them to the IVR system).

Yes, the service should be logically and naturally limited to the mobile carriers' destinations, as it is mobile subscriber that can easily be out of reach and the caller can get a service message instead of real connection and, thus, it is mobile carriers' destinations that would not be under suspicion when you mix fake FAS calls into real traffic. Though, it does not mean that you will not be able to mix in FAS into non mobile traffic. It is up to you to decide what message to play to the caller and to which traffic to apply the service.


Created by: astar, Last modification: Wed 03 of Aug, 2016 (19:47 UTC) by ccxmlmaster
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