[Asterisk-Users] Detecting Fax and bad CDRs

[Jim Sturtevant]

I used to own a company which made fax switches and yes your devise must
"answer" the call to detect the fax CNG tone or wait till voicemail answers
and try to detect the CNG tone while the voicemail greeting is being played.

-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Adam Goryachev
Sent: Monday, May 02, 2005 8:13 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] Detecting Fax and bad CDRs

On Mon, 2005-05-02 at 21:21 -0500, Matthew Boehm wrote:
> Here is the current scenario:
> 
> Someone calls my DID. It comes in on PRI. I do "Answer()" then "Wait(1)"
to
> see if there is a fax tone. If there is, goto fax context and do the fax
> thing.
> 
> If no fax tone, then "Dial(SIP/myphone,30)". If I don't answer in the 30
> seconds, goto Voicemail.
> 
> However! If the person were to hangup before the 30 seconds expired, the
> channel would get hung up but the disposition in the CDR (along with the
> billable seconds) would be inaccurate because I "Answer'd" the call
> beforehand.
> 
> Is there a way to change the disposition and the billable seconds to more
> accurately reflect what happened?
> 
> This really is only a big deal for inbound 800 calls; because if I answer
> the call and it is a person and they hang up before voicemail picks up, I
> have to charge the customer for those 10-15 seconds. Plus, I give
customers
> the ability to see their "missed" calls, which is based on a 0 billable
> seconds duration in the CDR.

There are two methods for detecting a fax (that I know of).

1) Allocate a specific DID for your faxes, so any call to that number
will be a fax
2) Answer the call, listen for the fax tone, and if you receive it, then
treat as a fax, else carry on.

AFAIK, you can't listen to the audio prior to answering the call. (You
can sometimes send audio prior to answering the call). So you can't tell
if it is a fax or not.

Personally, I presume you would need to bill your user for that 15
seconds, or else you will end up losing money. You answered the call,
therefore the telco is charging you, if you don't charge your user, then
you will lose.

Of course, I could be wrong, but I doubt it :)

I'd like to know how those 'home/soho' fax machines 'detect' an incoming
fax and allow the inside phone to ring, and only pick up if it is a fax
call.....

Regards,
Adam
-- 
 -- 
Adam Goryachev
Website Managers
Ph:  +61 2 8304 0000                        adam at websitemanagers.com.au
Fax: +61 2 9345 4396                        www.websitemanagers.com.au

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