[BC] Carterphone

[stanleybadams]

Well let me start, Donna is looking it up and I can give it a start...

Carterphone was the ability to add a telephone modem (cup style--telephone
handset inserted of all the kinds) to the AT&T phone system.  Remember that
when the over the counter telephones came out they had a ring equalivany
factor (this had to do with ring current--and they had to be properly
insulated.  Tom Carter was an old Texas two way boy and he was tired of
missing a dollar to do service for a client.  Now telephone distribution of
audio service via a transformer of the 211 type which is what one would use
on either the transmit or receive in.  If it was 4 wire without the loop,
then it would be a balanced circuit and the circuit would be mandatory to
keep the currents equal in both directions within relation to ground.  It is
still required in transmission systems that carry the equivalent the same as
a four wire circuit, even optical.  

Now in the "last mile of service" or within the loop as we call it. They use
a hybrid transformer in all units because it allows the phone to phantom the
ringing voltage and one side of the audio to ground.  A transformer is still
required, it is still a four wire circuit howbeit, in a phantom
configuration.  This is how we used to add the remote control DC powered
type, and only some manufacturer types, to the program circuit through a set
of 211 type transformers using the center tap to ground configuration.  Now,
that is much older than the Carterphone dision and it was perfectly legal
because of tariffs that the phone company filed with the state would allow
for that class of service.  They had to use that too to make PBX lights,
signally and etc work too.  If they placed it across the pair of wires it
would screw up everything especially in the customers ear.  So they
phantomed it.

Carterphone is what was the beginning which allowed MCI to get their foot in
the door and then to win in an anti-trust.  Which by the way they had to win
about three times before Bell would stop pulling circuits on their
customers.  


I hope I answered your original question, but if I did not Donna might give
it.  But in essence that is what and did happen along time ago.  In the loop
was 2 wire, all outside the local loop and thus being called long-lines was
four wire in nature.  The term round robin was just the nomenclature if you
wanted to allow each station to have a chance to feed the loop.  Now, if not
every station was going to feed the loop there would be no need for a round
robin for NEMO, unless it was a round robin for the telephone companies need
so as to restore service from an opposite direction should the main feeding
direction fail.

Stan Adams