[asterisk-users] Fax detection ...

[Jay R. Ashworth]

On Tue, Oct 03, 2006 at 08:44:16AM +0800, Steve Underwood wrote:
> >>>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?
> > 
> It is the age of the machines which has no relevance.

Ah.  My early memories of CNG tones suggested that early fax machines
did not actually send them.

> >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...
>
> I guess you touched many consumer grade fax machines, since *most* above 
> the very basic ones can do this in some way.

Yeah, the only real "pro" grade fax machines I've ever run across was a
Panafax I have that uses 3-inch core paper rolls, and I never really
got that working.

> Some have really fun behaviour. I used to suffer some Olivetti ones that 
> had several modes of calling and answering - Delay a while, to give 
> someone a chance to pick up first; Pick up, but remain silent and see 
> what the machine can hear; etc. Those Olivettis would only properly send 
> a fax to another Olivetti when they were in straight forward standard 
> mode. Now there's compatibility for you. :-)

Yeah: "I'm so compatible with everyone else that I'm not compatible
with myself" is kinda dumb.

>                                                A lot of other machines 
> offer similarly dumb modes of behaviour, but nothing quite so extreme as 
> those. When you investigate one of these issues, and ask the user why 
> the machine is not in simple answering mode, they are usually unaware it 
> is not. These modes get set largely at random on installed fax machines.

Yay.

> Now, it seems like these special modes should only affect answering. It 
> would seem they are mostly about doing what Asterisk is doing - waiting 
> silently for the 1100Hz tone. However, that's just too clean and simple 
> for the fax industry. They do a bunch of other dumb stuff to make things 
> more awkward, like call and only send something when they here 2100Hz.

What fun.

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