telecom@ucbvax.ARPA (10/07/84)
From: Jon Solomon (the Moderator) <Telecom-Request@MIT-MC>
TELECOM Digest Sunday, 7 Oct 1984 Volume 4 : Issue 97
Today's Topics:
detecting modems
Re: Phone company scanning for modems
more net.followup stuff
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Date: Fri, 5 Oct 84 16:30:36 pdt
From: braun%ucbic@Berkeley (Douglas Braun)
Does anyone out there have any references to any articles on the VLSI
ethernet controller chip that Intel, AMD, and others are producing?
Articles in practically-oriented magazines such as Electronic Design
News would be quite useful.
Thanx,
Doug Braun
P.S. Please mail replies directly to above address at Berkeley.
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Date: Fri, 5-Oct-84 20:13:57 PDT
From: Lauren Weinstein <vortex!lauren@RAND-UNIX.ARPA>
Subject: detecting modems
Since modems on long-distance voice-switched circuits usually need to
trigger the echo-suppressors along the path to ensure a full-duplex
connection (via a 2225 Hz tone) it would be theoretically possible for
the triggering of those suppressors to be used to indicate that a
modem call was in place over that circuit. With CCIS, determining the
called and calling numbers would be practical.
Without monitoring of the data, however, there'd be no way to know
whether it was business data, residential data, hearing-impaired TDD
communications (ASCII mode), or something else.
--Lauren--
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Date: Sat, 6 Oct 84 13:21:33 edt
From: mar@mit-borax (Mark A. Rosenstein)
Subject: Re: Phone company scanning for modems
What he may be thinking about is echo suppression on long distance
lines. Long distance trunks have circuitry to make it easier for
voice to be understood, but which would screw up modem traffic. Thus
these trunks detect the frequency which is used as carrier on the
answer end of the connection in Bell 103 (the same frequency is used
in most other protocols), and when they detect it turn off the echo
suppression.
As far as I know that is the only place the phone company checks for
modems right now, and they don't do anything else with that
information. They do not have these circuits on individual customer
lines, and because of the expense probably never will.
-Mark
mar@mit-borax.arpa
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Date: Sat, 6 Oct 84 18:53:31 EDT
From: Jon Solomon <jsol@bbncca.ARPA>
Subject: more net.followup stuff
From: paul@dual.UUCP (Baker) Organization: Dual Systems, Berkeley, CA
Central offices do not and do not need to know if a modem is being
used. On the other hand Echo suppressors that are used to prevent you
hearing your own voice returned after a few seconds on long lines,
need to be disabled for a full-duplex Modem to work. It does this by
detecting the answer tone given by the Modem. Note that this is the
same tone for all Bell standard Modems. Digital central offices are
in no better position to interpret information passed through them.
There does seem to have been an interest in the past by phone
companies to try and charge Modem users more than voice users. So far
none of them have been successful.
Paul Wilcox-Baker
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End of TELECOM Digest
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