[asterisk-users] Fax detection ...

[Lee Howard]

Jay R. Ashworth wrote:

>On Sun, Oct 01, 2006 at 02:58:37PM -0700, Lee Howard wrote:
>  
>
>>Well, fax detection isn't entirely reliable anyway.  Even if you assume 
>>that your fax detection feature and operation is flawless in properly 
>>detecting fax tones (and that most likely would be a specious 
>>assumption), not all calling fax machines send fax tones.
>>    
>>
>
>So, y'know, that assertion gets made a lot.
>
>What's the turn rate of fax machines in the market? 3 years?  5?  CNG
>tones are *well* over 10 years old, no?
>
>What percentage of fax calls are sent without CNG tones these days?
>

I couldn't say, myself, because I've not run statistics on it - and even 
if I did it would be skewed to the pool of fax systems used by the 
industry where I took the sampling.

The reason that some machines don't send fax tones isn't usually because 
they are old, but rather because the manufacturer or user have 
deliberately made it behave that way.  For example, with a lot of 
traditional modem hardware, in order to detect ringback (used on analog 
lines to determine whether or not the call was even answered), CNG is 
often disabled.  Furthermore, some fax senders (in particular fax 
*servers* - especially those used for fax spam) deliberately disable CNG 
to avoid annoying the receiver in the event that a number is misdialed.

We don't care about that fax spam, I know.  However, fax spammers often 
use the same hardware and software that other people will use for 
non-spam purposes.

Lee.