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From: gammafax!mikes@uunet.uu.net (mike spann)
Newsgroups: comp.dcom.telecom
Subject: Re: Phone/Fax Switchbox -- Do They Work?
Message-ID: <10235@accuvax.nwu.edu>
Date: 30 Jul 90 22:48:25 GMT
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In article <10225@accuvax.nwu.edu> cjp%megatek.UUCP@ucsd.edu
(Christopher J. Pikus) writes:

>	I've been considering getting a fax machine for home use but
>am hesitant to connect it to my primary residence line. Mainly How do
>I prevent the FAX machine from answering calls meant for myself while
>receiving data calls.

>	Now, I have seen these phone/fax switchboxes that allegedly do
>this but I'm not sure how it is done. So my question is: how does such
>a critter work? My only theory is that the originating fax machine
>sends a pilot tone to signal the answering machine (or switchbox) that
>a fax transmission is coming in.

I have seen two common types phone/fax switch boxes.  

One uses a voice prompt and requires the caller to enter a touch tone
digit to get the answer machine/fax and will get the fax/answering
machine otherwise.  This works ok if all your friends have touch tone
and you have the default be to the fax machine.

The other box (and the one I would select) uses the little known fact
that audio energy is carried down the phone line when the phone is
ringing.  (This is commonly known to thiefs who sometimes talk to each
other without answering the phone).  An automatic fax machine sends a
calling tone every three seconds while waiting for the phone to be
answered.  The phone/fax switch box listens on the line for this
'calling tone' and routes the call to the fax machine if one is heard.
The box never answers the phone which I consider an advantage.  This
way you can have a real-live phone the voice connection and a fax
machine on the other.  People don't have to pay to call when you
aren't home.  (I personally hate answering machines..)

The disadvantage of this approach is that manually dialed faxes and
some older fax machines do not send the calling tone and will not be
properly routed to the fax machine.  Fortunately, in practice, very
few people 'manually' dial numbers.  They place the paper in the fax
machine, press the buttons and let the machine do the work.


Michael Spann 
Voice:  +1-408-744-1430			Fax:    +1-408-744-1549
UUCP:   ...!uunet!gammafax!mikes   	CIS:    73747,441