Hello Ahmed,

IMHO the best solution is policy:

1) gather statistics from your CDRs (FreeSWITCH has lots of variables
that you can use in your CDRs)
2) place test calls in cases where the stats show a possible problem
3) send a trouble ticket to the offending carrier in cases of FAS
and
4) stop using the route until the "problem" is fixed.

I hear what you're saying. And how much is the time and man effort involved in manually dealing with this ?

Unfortunately, it is a lot of work. In fact it is a 24x7 manual work... What makes things a bit easier is that a FAS route will have a short setup-connect delay, and statistics will definitely show a heavily FASed route, although a route with a small percentage of FAS will still go under the radar. And of course, using statistical methods doesn't give you results in real time...

We have experimented with tone_detect app as Anthony Minesalle suggested for detecting tones to apply to FAS problems and it works very well. But after a while we dropped the whole FAS detection idea because of the so many different FAS scenarios out there... Plus, quite a few methods that monitor audio involve decompressing the incoming audio before processing it. This means that you need to have audio transcoding on FS, which a bad things in terms of perceived audio quality and CPU power/scaling. In that case you would almost certainly need quite a few G729 codec licenses, as most carriers use this codec to send you their traffic.

Nonetheless if you want to pursue this and you need help I'd be happy to assist, as FAS is a huge problem for carriers.

Best regards,
Vlasis.