From: orville%weyrich@tnet.com (Orville R. Weyrich)
Subject: Re: Fax/Voice switch
Reply-To: tnet.com!weyrich!orville
Organization: Weyrich Computer Consulting
Date: Fri, 21 Aug 92 05:25:34 GMT

In article <1992Aug17.192849.15076@u.washington.edu> newsman@milton.u.washington.edu (Chris Ricci) writes:
>Hi.  This is a re-re-re-post.  Yes I screwed up my first post.  I am looking
>for a switch that will allow me to use a modem on the same phone line as my
>regular phone calls(voice).  I didn't get any response to a question about
>a voice/modem switch or the plans for one so now I'm curious if anybody 
>knows whether a fax/voice switch will perform the same job.  If you have even
>the slightest idea or suggestion I would appreciate it.  Thank you very much!

[To the best of my knowledge -- I am open to corrections/additions:] 

Phone/fax switches work by answering the
incomming ring and listening for a fax machine to signal a request to
establish a session.

If no request is heard in a prespecified period of time, then a ring
is generated on an outgoing line to which a phone is attached. A person
or a modem may answer. Some switches will generate the ring for the
phone/modem line concurrently while listening for a fax "mating call".

The problems with this approach are that:

	1) if the incomming caller is a person, they may hear the phone
		be answered but not be connected to the other party 
		immediately, which can be confusing. Some switches will also
		send out a generated "ring" to the caller so that the caller
		thinks that the destination has not yet answered, when in fact
		the destination has answered and is listening for a fax mating
		call.

	2) the calling modem normally waits for the destination modem to 
		issue its "modem mating signal", so the switch can't 
		distinguish between a human caller that is silent and a 
		"coy" modem waiting to be "seduced". If you are willing to
		require incomming modem callers to use "reverse signalling"
		then the calling modem will generate its mating call first
		and the switch can [in principle] detect the incomming
		call as a modem session and switch the line appropriately.
		The mating call of a modem is different from that of a fax,
		so the switch can [in principle] distinguish between an
		incoming fax call and an incoming reverse-signalling modem
		call. Not all switches actually CAN recognize an incoming
		reverse-signally modem. Not all originating modems are
		capable of generating a reverse signal, and not all
		destination modems are capable of responding to a reverse 
		signal.
	
As you can see, there are a number of trade-offs involved. I have a switch
called a "Versa-Link ATX-300" that I bought from a friend that has moved
away [don't know where] that has all of the capabilities I described [but I
haven't actually tried them all]. I use it to switch between incomming fax and
incomming modem [not reverse signaling] but not voice. It works more or less,
but not with all incoming fax [some fax machines don't generate a recognizable
mating call in originate mode, and hence get transferred by default to my
modem]. Also, I have to configure my modem to wait until about the 4th ring
to pick up an incoming call in order to allow the swtich adequate time
to recognize an incoming fax [otherwise the fax call might get answered by the
modem]. Some incomming modem calls don't wait a sufficient number of rings
before giving up.

A technically better solution is in principle available in some calling
areas. For a small monthly charge the phone company can give you several
different phone numbers that all ring on the same one physical phone line
in your house. The different numbers generate different "ring" signals
[made distinct by varing the timing pattern of ring on and off]. This
is intended to be recognizable by different people so that just by listening
to the ring you can tell if the call is for Mom, Dad, or Junior, etc.

In principle a switch box could be made to listen to the incomming 
distinctive ring pattern and direct the ring to one of several different
outgoing ports without actually answering the incomming call and listening
for a fax or modem [there would be a delay of at least one ring cycle,
however].

I say "In principle" because I have heard that such switches exist, but
do not know where to buy them or how much they cost.

ANYONE ON THE NET THAT DOES KNOW THE WHERE/HOW MUCH of these "distinctive ring"
switches, please post -- a product review would be even better!

Thanks

orville

--------------------------------------       **********************************
Orville R. Weyrich, Jr.                          Weyrich Computer Consulting
Certified Data Processor                       POB 5782, Scottsdale, AZ 85261
Certified Systems Professional                      Voice: (602) 391-0821
Certified Computer Programmer                Internet: orville%weyrich@tnet.com
--------------------------------------       **********************************

Newsgroups: comp.sys.ibm.pc.hardware