Index Home About Blog
From: "Fred R. Goldstein" <>
Subject: Re: Historical Query: Carterfone
Date: 30 Mar 90 21:15:27 GMT
Organization: Digital Equipment Corp., Littleton MA USA

In article <>, writes...

>There was a landmark court case that led to a ruling that
>non-telco devices could be connected to the net.  That led to DAAs
>(standing for Direct Access Arrangements, I think) and then to FCC
>registration.  The case is referred to as the Carterfone Decision (I

Carterfone occured in 1968.  Prior to that, the FCC and state
regulators all allowed the local telephone companies to have tariff
restrictions prohibiting any "foreign" attachments.  Only telco could
attach telephone sets, modems, PBXs, etc.  The sole exception was
wirephoto machines, which newspapers won under a First Amendment
claim!  (And that didn't mean any fax, either.)  Even shoulder rests
for handsets were officially forbidden!  (Not that they could enforce
that one.)

The Carterfone itself was an acoustic coupler for land mobile radios.
It was used to allow oil field drill rigs (radio equipped) to patch
calls into the telephone network.  Ma Bell was insane to complain
about it, but in their arrogance, they tried to prohibit people from
using it.  The FCC had changed its stripes by then and used this case
to allow the competitive provision of telephone terminal equipment,
and the rest is history.

Before Carterfone, a 300 baud modem rented for $25/month.

Fred R. Goldstein  voice:  +1 508 486 7388 
opinions are mine alone, sharing requires permission

Date: Sat, 29 Feb 92 19:35 PST
From: (John Higdon)
Organization: Green Hills and Cows
Subject: Re: Exactly What Was Carterfone? writes:

> "It was then permitted to connect devices to the Bell System via a
> small white box on the wall called a DAA (direct access adaptor), which
> is essentially an isolation transformer.  Later the need to use a DAA
> was eliminated in most situations ..."

I object! :-) As someone who was subjected to the full frontal hell of
that era, I demand to be heard! It was not a "small white box". The
post-Carterfone desision era was a time of CDH, STC, STP and a host of
other "coupling devices" that seemed to be designed to cripple
telephone service at every turn.

If you had an answering machine at your home, you had to order an
"STC" coupling device. This carried a $100 installation charge and a
hefty $5.50/month extra charge on your phone line. For this you got
quite a gadget. It was full of relays, transistors, and a bunch of
other components. It provided a fully isolated loop to which you
connected your answering machine. It was so isolated that it did not
pass CPC (loop current interruption) or ring voltage. Your answering
machine had to be capable of receiving ring current on a third wire.
The STC would generate its own 20 Hz ring voltage with a relay that
chattered twenty times a second, alternating the 70 volts DC that was
generated elsewhere in the unit.

The CO ring detector would take a full half-second to recognize an
incoming ring, so your device only got little bursts of that bogus
ring voltage. Voice transmission loss through the coupler was over one
decibel. It required AC power, so your answering machine would be
inoperative during a power outage, even if it ran on batteries.

The other major coupler was the CDH, and was used to connect PBXes to
the network. These required five pairs for each line between the
interface and the PBX. The extra wires signalled ring up, battery
present, line siezure, etc., in addition to the actual audio pair. The
cost for a CDH was the same as for an STC. In some phone rooms, one
could find frame after frame full of CDH cards, each card costing its
telephone customer $5.50 per month.

But then, as you may know, the phone company had to give it all back.
Every last dime. All installation charges. All monthly charges. And
interest on all charges EVER collected for the installation or use of
these devices. It almost made it all worthwhile -- but not quite.

        John Higdon         |   P. O. Box 7648   |   +1 408 723 1395      | San Jose, CA 95150 |       M o o !

Index Home About Blog