[asterisk-users] Fax detection ...

[Jay R. Ashworth]

On Mon, Oct 02, 2006 at 10:43:44AM +0800, Steve Underwood wrote:
> 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 relevance does that have to CNG? It was a feature of the original 
> spec 30 years ago.

Well, perhaps I wasn't paying attention, but I thought that CNG tones
*had as their purpose* making receive FAX detection trivial.  That
would tend to make the question on-point, would it not?

> >What percentage of fax calls are sent without CNG tones these days?
>
> Quite a lot. A large number of FAX machines have CNG turned off. On many 
> machines, if select features like sharing a line between FAX and 
> answering machine CNG, CED and various other useful behaviour might be 
> disabled.

My personal experience is that I've never seen a consumer-grade fax
machine with send-CNG turned off, and I don't *think* I've ever seen
one on which there was a knob *to* turn it off; I would be less sure
about fax modems -- those may have a knob, but I would expect it to
default on.

Could you expand on what behaviour you think CNG breaks?  Cause I'm not
modeling it, mentally...

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra at baylink.com
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