Re: History AT&T early modem developments? [telecom]

To pick up on a couple of points...

When I said the Model 33 probably cost about the same as the Model 32,
I was only talking about the bare machine. The TWX version of the
Model 33 and Model 35 machines was quite costly because of the complex
call control unit that connected to the 101 Data Set (modem). There
was a 99 wire cable between the two, which around Teletype was
considered the epitome of awfulness. Then there were so many variations
of the TWX call control unit: rotary dial, TouchTone dial, card dialer,
and loudspeaker versus hand receiver.

There was a plan, which I believe was never implemented, to have a set
of call-progress lights on the machine that would show dial tone,
ringing, busy tone, reorder, connected, etc. I don't believe they
ever developed a modem that could reliably recognize all these conditions.

I was told that some of the Bell operating companies avoided the high
price of the TWX Model 33/35 equipment by buying the simple private
line models and attaching them to 103 Data Sets, which had all the
telephone stuff internal to the modem package.

The 100-series Data Sets, or at least the 103s, had strapping options
allowing either of the two tone pairs to be used for originate vs.
answer direction of transmission, and for either tone of either pair
to represent mark. These three options allowed the same modem to be
used for eight different mutually-incompatible services. One of these
was TWX, another was Data Phone which allowed voice and data transmission
and was charged for at voice rates. Then there were WADS (wide area
data service) and something called WADS-Prime that was yet another
service. WADS was shot down by the FCC; and I never knew what WADS-Prime
and the other services were intended to be.

Concerning time sharing, a lot of the early time sharing systems were
half-duplex. I well remember the computer prompting for Login: and
then it would prompt for Password: and type a bunch of overstrike
characters to create a black mess so that your password would not
appear readable on the paper.

.

Relevant Pages

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