Hi Valsis, Thanks for this. My line of thought is to tone-detect secondary ringing tones post 200(OK) to detect FAS (False Answer Supervision). This should eliminate at least a good proportion of calls, and it can be done real time through a script/modules/...etc. Working along this thought, at least you are minimising the hit cost-wise to a few seconds at most. As to answering machines and fake conferences, fake network messages ...etc, one can possibly use voice detection, perhaps with heuristic and statistical training. Just a thought .. Regards, Ahmed. 2010/1/8 Vlasis Hatzistavrou (KTI) <vhatz@kinetix.gr>
Hello Ahmed,
I don't think there is a reliable way to detect FAS on a per call basis. Even audio detection software can be confused by strange ringtones, answering machines, etc.
The most reliable way we have found is to use statistics from CDRs and see if the INVITE-to-200(OK) delay averaged over a number of calls appears to be too small. If it is, then it is possible that you got FAS for those calls.
But this can only tell you if you have been experiencing FAS in past calls, ie you will not know you are getting FAS in real time.
It is still useful however: after you detect a possible FAS case via statistics you can place a few test calls yourself to verify that there actually exists FAS (and this is the only information that a carrier will accept in a trouble ticket to prove to them that they actually give you FAS).
I hope this helps.
Best regards, Vlasis Hatzistavrou.
On 8/1/10 3:05 πμ, Ahmed Naji wrote:
Hi everyone,
Was just wondering what/if anyone is doing any work on FAS detection and spoofed ring tones. Be great to discuss some ideas.
Regards,
Ahmed.
-- Ahmed Naji
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-- Ahmed Naji