[asterisk-users] Fax detection ...

[phil.dawson at marnock.com]

It all boils down to this:  If they don't send a tone I won't get the fax.
Its like my email now with DNS blacklists enabled.  If they have a dial-up
ADSL account they can't send me mail as my server denied them.  Different
technology, same problem.  Whatever they invent next will, more than
likely, have the same problem.

If they really want me to receive whatever it is they want me to see ...
they can post it  :-)   that nearly always works too!


Phil.



                                                                           
             Lee Howard                                                    
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Jay R. Ashworth wrote:

>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.
>
>

On fax modems the way to silent-dial (and I believe that this was a norm
from early-on) to to add an "@" at the end of the dialstring:
"ATDT5551212@".  I would be very surprised to find any modern fax modem
that does not have this capability.

I don't know of any specific fax machine that has such a "knob" to turn
CNG off.  But my contention wasn't that it was consumer-grade fax
machines that were the main culprit here, but rather fax servers (PCs
with fax modems in them).  And depending on what industry you are
sampling, those may actually consitute a fair amount of the caller
pool.  (For example, some industry software - like insurance agent
application software - will have built-in fax features that will use the
PC's fax modem - and the application vendor may insist on that feature
being used.)

I cannot cite specific software that does it, but I suspect that most
fax application developers are aware of the ability to silent-dial, and
the reasons why it may be employed.  As I've said before, one reason, as
an example, is to make the modem capable of hearing ringback - so that
it knows if the call has been answered or not (which itself is a
unreliable endeavor).  Another reason is to avoid annoying the receiver
moreso on a call to a wrong-number.

It's off the topic of silent dialing but on the topic of this thread...
Brother fax machine manuals state that it is possible for them to
erroniously detect certain voices or music as CNG tones, and if that
becomes a problem to disable fax detection.  And that's basically
another point along the lines that say that fax detection is not
completely reliable.

Lee.

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