Hello Alfredo, Please see comments inline: On 10/4/10 6:51 μμ, Alfredo Quiroga-Villamil wrote:
All:
A while back I tried to solve a false answer supervision issue I was intermittently receiving from underlying carriers. Back then I tried to find a solution using asterisk but had other pending things and put this off until now.
Does anyone have any recommendations on how to possibly handle or get around FAS using FS. If I am not mistaken what would be needed is to have something that upon receiving the first 200 message, it simply ignores it, never propagating it and waits for the next 200. I can control this now a little bit better since it's only happening when the calls are sent to a couple of GrandStreams (FXO).
As you have already noticed, when you get FAS, you receive a 200 before the call is answered. But I have never seen a second 200 when the call is really answered by the remote end, because after you receive the first (and only) 200 message, the call is considered as being properly connected, with RTP going both ways and all. A FAS giving carrier will take care to not send you another 200 when the call is answered. So, I don't believe there is a way to detect and remove FAS successfully, because to your equipment, it just looks like a properly answered call. What you can do is gather batches of CDRs and extract statistics about the time delay from the INVITE you send to the 200 you receive. If you measure it too short, then you PROBABLY have FAS, and you'd still need to place a test call yourself you verify it. You will not be able of course to tell which exact calls had FAS, but you'll be able to have a clue about whether there is FAS present on the route or not. And this means that you'd still have to do a lot of work yourself, like watching stats, placing test calls etc. Even if you were able to find a way to remove FAS on a route, that would mean that your termination carrier would still charge you for the time difference between the 200 that he sends you and the BYE. And you'd still pay for a longer duration than what you would charge to your customer if you were able to remove FAS. This is why my opinion is to watch statistics, place test calls and in the event of a carrier giving FAS, remove it from your routing. Sooner or later, they will either stop giving you FAS or you will stop doing business with them. Best regards & good luck, Vlasis Hatzistavrou.