Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: motcid!segal%cell.mot.COM@uunet.uu.net (Gary Segal)
Newsgroups: comp.dcom.telecom
Subject: Re: Data Over Voice
Message-ID: <2038@accuvax.nwu.edu>
Date: 11 Dec 89 20:09:27 GMT
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X-Telecom-Digest: Volume 9, Issue 567, message 3 of 6


steele@ee.ecn.purdue.edu (Richard Steele) writes:

>Here at Purdue U., we now have access to something called data over
>voice (DOV) units.  These are small boxes, about the size of a regular
>modem, that gives the user a 9600 bps asynchronous data line to the
>University computer.  Not only is the bugger faster than a modem, _but
>it leaves the phone free for regular use_.  We can still receive and
>make calls with the DOV working with no obvious distortion on the
>line.  Thus, in addition to having a reasonably fast connection (and I
>used to think a 2400 baud modem was speedy!), I don't have to take the
>wrath of my roomates for hogging the phone line all night long.

>The DOV unit connects to the phone line before any other equipment;
>i.e. there's are line in and line out jacks.  In addition, just like a
>Hayes Smartmodem, there are a plethora of LEDs on the front like CD
>(carrier detect), RD (receive data), SD (send data), etc.

>Question: How would something like this work?  The phone company
>_does_ need to make some changes on their end, but the phone line
>remains the same.

>So, what magic is involved here?  Thanks to all who respond...

Carnegie-Mellon University has had something called "Metropolitan
Campus Network" (MCN) for a while (since fall 1986, I think).  It
gives people on certain CO's a 9600bps data link to the campus
computing network.  It is implemented using Gandolf DOV modems (model
number escapes me), which sounds very much like the beast Purdue is
using.  When installed, the connection looks like this:


        +-----------+	| 2-wire to CO	|   +-----------+
 =======| DOV Modem |=======================| DOV Modem |=========
 2-wire |           |	|		|   | in a Bank |Many Pairs
 to VF  |           |	|		|   | O' DOVs   |to CO
 equip. +-----------+	|		|   +-----------+equip.
 (phones,       !	|		|	!
  modems,       !	|		|	!
  faxes...)     !	|		|	!
		!	|		|   Many RS-232 links to
    RS-232 to computer	|		|   data switches &
			|		|   terminal concentrators
			|		|
    Customer Premise	| Poles, etc...	|   Central Office

VF = Voice Frequancy

How does it work?  Simple, if the line between the CO and the customer
premise is pretty good, you can get more than 300-3400Hz bandwidth out
of it.  The DOV modems use carrier frequancies above 3400Hz.  They
have a filter that sits between the DATA/Voice side and the VF side
that removes the data signals.  In addition, all of the normal
telephone signals are passed through without changes.  At the CO end,
the data is "peeled" off before the channel banks or other such CO
equipemnt.  Thus, the DOVs are transparent to VF and telephone
signaling.

In order for this to work, the pair from the CO to your premise must
be pretty darn good.  When MCN was first offered by Bell of PA and
CMU, they listed the exchanges that you could get it on.  I believe
they had installed DOV shelves in three CO's, so if you were attached
to any of those, you could get it.  In addition, they stated that if
you were more than a certain distance from the CO (2 or 3 miles, I
think), it wouldn't work.

There was also talk of making a 64Kbs link availible, however I don't
know if it was going to be by DOV or ISDN.

Oh yeah, it was fairly expensive for your average student, something
like $100 to install, $200 for the DOV and $25 a month.

Maybe somebody at CMU can bring us up to date on the current state of
MCN.


Gary Segal, Motorola C.I.D.			1501 W. Shure Drive
 ...!uunet!motcid!segal				Arlington Heights, IL 60004
Disclaimer: The above is all my fault.		+1 708 632-2354