[Freeswitch-users] Detecting FAS?

Avi Marcus avi at avimarcus.net
Mon Mar 2 13:33:56 UTC 2020

I've yet again had users reporting issues and I found it there's FAS.
I'd like to find or create something that notices and logs these issues
immediately, before potentially weeks of customers experiencing degraded
service. Before I re-invent the wheel, I'm asking if someone has a wheel

I looked at these particular PCAPs and the ringing is quite clear to hear.
Is there some scripts around that can flag calls, either based on simply
the CDR or even with the PCAP as FAS? (e.g. FAS calls will rarely be over 2

(Although, apparently there's many types of FAS. One more is to play a ring
tone for 10-20 seconds and THEN try to connect the call. That way they get
at least free 20 seconds of billable time and then proceed with business as

https://blog.kolmisoft.com/fraud-false-answer-supervision-fas/ mentions key
indicators in the CDR, but this isn't enough to definitely pin it as FAS.
This could also occur upon reaching voicemail.

   - Short phone calls.
   - A caller which hangs up nearly 100% of the time.
   - High answer seizure ratio.
   - Lower ACD.

They also mention this, which is what I'm interested in: "RTP audio signal
processing: detection of voice, silence or ring-back tone."

Is there some simple way to detect ring tones in the audio playback (which
I might have to cut to ensure it's after the billing has actually started
if the audio ring tone was passed in band)


-Avi Marcus
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