History AT&T early modem developments? [telecom]

History AT&T early modem developments? [telecom]
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History AT&T early modem developments? [telecom] hancock4 03-10-2008
Posted by on March 10, 2008, 6:30 pm
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In response to commercial and military demand, in 1941 IBM developed
equipment that allowed transmission of data over telegraph lines, be
they Western Union or AT&T. In telegraph transmission, there is no
modulation, the bit pulses themselves are sent out over the line. The
internal IBM code was converted to Baudot code for transmission, then
back to IBM for subsequent processing.

This allowed remote offices to transmit things like inventory
transactions to the central office to keep records up to date in a
timely fashion. (Short wave radio was also used worldwide.)

Line costs were relatively cheap (leasing an AT&T private telegraph
line was much cheaper than a voice grade line) but they were slow,
about 50-100 bits were second.

In 1954 IBM developed a more sophisticated system that included error
checking and better controls, and modems to allow transmission over
private leased voice grade phone lines. It appears that AT&T allowed
users to supply their own modems in private line service. A machine
could run up to 300 bits per second, but the line could support four
of them simulataenously yielding an effective throughput of 1,200 bits
per second.

It doesn't appear AT&T was interested for data communications over its
dial-up voice network. Finally, it appears that in 1958 AT&T
introduced pioneer modems and in 1960 introduced popular dataphone
units. In 1960 IBM introduced high speed data communications where
magnetic tape was used.

Some other manufacturers were developing modems as well at that time,
including Stromberg Carlson.

Would anyone be more familiar with 1950s AT&T activities, or lack
thereof? I'm curious why AT&T wasn't more aggressive about this; IBM
had been working with AT&T all along for the leased line products.

One explanation may have been the dial-up toll network may have been
too poor quality to handle this as compared to leased private lines.
Keep in mind the toll bandwidth was reduced in WW II to as narrow* as
possible to faciliate war traffic and that continued after the war due
to high demand. I don't know the particulars, but I doubt 1200 would
work that well on a degraded network. Also there was the problem of
echos on 2-wire networks that was mostly switched manually.

Any explanation would be appreciated.

* Also, any info on the wartime narrow bandwidth would be appreciated.

Thanks!


NMFall 20%
Posted by Reed on March 10, 2008, 11:12 pm
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hancock4@bbs.cpcn.com wrote:
> In response to commercial and military demand, in 1941 IBM developed
> equipment that allowed transmission of data over telegraph lines, be
> they Western Union or AT&T. In telegraph transmission, there is no
> modulation, the bit pulses themselves are sent out over the line. The
> internal IBM code was converted to Baudot code for transmission, then
> back to IBM for subsequent processing.
>
> This allowed remote offices to transmit things like inventory
> transactions to the central office to keep records up to date in a
> timely fashion. (Short wave radio was also used worldwide.)
>
> Line costs were relatively cheap (leasing an AT&T private telegraph
> line was much cheaper than a voice grade line) but they were slow,
> about 50-100 bits were second.
>
> In 1954 IBM developed a more sophisticated system that included error
> checking and better controls, and modems to allow transmission over
> private leased voice grade phone lines. It appears that AT&T allowed
> users to supply their own modems in private line service. A machine
> could run up to 300 bits per second, but the line could support four
> of them simulataenously yielding an effective throughput of 1,200 bits
> per second.
>
> It doesn't appear AT&T was interested for data communications over its
> dial-up voice network. Finally, it appears that in 1958 AT&T
> introduced pioneer modems and in 1960 introduced popular dataphone
> units. In 1960 IBM introduced high speed data communications where
> magnetic tape was used.
>
> Some other manufacturers were developing modems as well at that time,
> including Stromberg Carlson.
>
> Would anyone be more familiar with 1950s AT&T activities, or lack
> thereof? I'm curious why AT&T wasn't more aggressive about this; IBM
> had been working with AT&T all along for the leased line products.
>
> One explanation may have been the dial-up toll network may have been
> too poor quality to handle this as compared to leased private lines.
> Keep in mind the toll bandwidth was reduced in WW II to as narrow* as
> possible to faciliate war traffic and that continued after the war due
> to high demand. I don't know the particulars, but I doubt 1200 would
> work that well on a degraded network. Also there was the problem of
> echos on 2-wire networks that was mostly switched manually.
>
> Any explanation would be appreciated.
>
> * Also, any info on the wartime narrow bandwidth would be appreciated.
>
> Thanks!
>

As someone who has worked with and for modem vendors since 1965, I
have also tried to find a good written "History of Modems". Most
people today think modems were invented at the same time, and just
for, the Internet.

By the mid 1960's, many types of modems were available not only from
AT&T/Bell, but such as Rixon, GTE Lenkurt, Milgo, Codex, Paradyne,
Anderson-Jacobsen, Vadic and others.

Most "history" articles on the Internet today tend to be the same
basic, general info re-hashed. I have found the following sites to be
of some value re the really early development stages.


http://en.wikipedia.org/wiki/Modem
http://en.wikipedia.org/wiki/SIGSALY
http://www.ieee.org/web/aboutus/history_center/oral_history/abstracts/rosen440ab.html
http://www.infopackets.com/channels/en/pause_for_thought/word_of_the_day/2005/20050918_modem.htm

--reed


Posted by Scott Dorsey on March 11, 2008, 12:29 pm
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>
>Would anyone be more familiar with 1950s AT&T activities, or lack
>thereof? I'm curious why AT&T wasn't more aggressive about this; IBM
>had been working with AT&T all along for the leased line products.

Lack thereof? AT&T had their own huge TWX data network at the time.

http://www.baudot.net/docs/kimberlin--telex-twx-history.pdf

>One explanation may have been the dial-up toll network may have been
>too poor quality to handle this as compared to leased private lines.

Not relevant, as most of the leased private line voice systems out there
were leasing from AT&T.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


Posted by on March 11, 2008, 10:56 pm
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On Mar 11, 12:29 pm, klu...@panix.com (Scott Dorsey) wrote:
> >Would anyone be more familiar with 1950s AT&T activities, or lack
> >thereof? I'm curious why AT&T wasn't more aggressive about this; IBM
> >had been working with AT&T all along for the leased line products.
>
> Lack thereof? AT&T had their own huge TWX data network at the time.

AT&T's TWX network dated from at least the 1930s. But it was direct
pulse from the subscriber.

AT&T had a separate tarrif for "20 ma" and "60 ma" lines in which
pulses were directly transmitted. These were discontinued some time
ago, but were used to drive all the teletypewriters out there.


> >One explanation may have been the dial-up toll network may have been
> >too poor quality to handle this as compared to leased private lines.
>
> Not relevant, as most of the leased private line voice systems out there
> were leasing from AT&T.

I don't understand. What I'm saying is that back in the 1950s the
quality of the dial-up long distance network may have been inferior to
that of private lines.

As mentioned. the bandwidth of voice long distance in that era was
narrowed to 2-3 Khz instead of 4 Khz in order to squeeze out more
capacity on limited toll circuits during the war.


***** Moderator's Note *****

I don't think your take on the "60 speed" TWX is correct: AFAIK, they
used ordinary phone numbers connected to regular business exchanges,
and that would require modems.

TELEX, OTOH, _did_ use DC signalling, with specially constructed step
exchanges.

Who is our resident TWX expert? Comments?

Bill Horne
Temporary Moderator

(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)


Posted by Scott Dorsey on March 12, 2008, 11:34 am
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>On Mar 11, 12:29 pm, klu...@panix.com (Scott Dorsey) wrote:
>> >Would anyone be more familiar with 1950s AT&T activities, or lack
>> >thereof? I'm curious why AT&T wasn't more aggressive about this; IBM
>> >had been working with AT&T all along for the leased line products.
>>
>> Lack thereof? AT&T had their own huge TWX data network at the time.
>
>AT&T's TWX network dated from at least the 1930s. But it was direct
>pulse from the subscriber.
>
>AT&T had a separate tarrif for "20 ma" and "60 ma" lines in which
>pulses were directly transmitted. These were discontinued some time
>ago, but were used to drive all the teletypewriters out there.

Right. This is what I mean by a "data network."

Note that the TWX network by the 1950s was using FSK modems to transmit
data, so that many different data circuits could be put onto one voice
line. The idea basically came out of the radioteletype world. The loop
line to the customer was DC, but the cross-country trunk was FSK.

When we talk about "modems" we are talking about two different things.
First of all, there are high speed modems that are intended for use on
wideband leased lines. That's what IBM came up with... they had some
repeating machines where you could put a deck of cards into a reader and
have copies spit out of a punch many miles away. This was a big deal for
far-flung business organizations and was the predecessor to RJE. This
is basically a data network, running over analogue lines.

THEN, we have the dialup modem, which is really just a cheesy workaround
to get low-rate data over voice-grade lines, so people could use existing
infrastructure for data.

>I don't understand. What I'm saying is that back in the 1950s the
>quality of the dial-up long distance network may have been inferior to
>that of private lines.

Most of the private line networks were built with trunks leased from
AT&T. The railroads had their own voice networks running on their own
cables, but if you called from one Ford Motor Company office to another
Ford Motor Company office over Ford's internal voice network, you were
doing it over lines leased by Ford from AT&T.

>I don't think your take on the "60 speed" TWX is correct: AFAIK, they
>used ordinary phone numbers connected to regular business exchanges,
>and that would require modems.

By the sixties and seventies, many folks were using dialup lines to
connect their local TWX machine to the network. This is fine for
outgoing messages, but the remote service has no way to inform you
of urgent incoming messages.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."



***** Moderator's Note *****

I think we're talking about differing things here.

The Teletypewriter Exchange Network (TWX) used modems, first at 60
speed and later, when "Four Row" (ASCII) machines were introduced, at
110 speed. The three-row machines used Baudot and could dial each
other directly over regular business grade dial tone lines. It was
operated by AT&T.

The TELEX network used 66 speed machines, connected directly to the
loop pairs that served them, without modems. It was operated by
Western Union.

When four-row machines were introduced to obviate the need to have
specially trained operators, they were assigned numbers with "TWX"
area codes 710, 810, or 910. These were actually Terminating Toll
Center codes in reverse, i.e., a machine with a 710 number could be
reached directly by using TTC code 017. The special codes were needed
to maintain compatibility with the older 60 speed units: when one
dialed the other, a speed and code converter was used to connect them
together, and the 110 speed machine could be put in "Restrain" mode by
the C.O. equipment, forcing it to wait while the 60 speed machine
caught up.

Then, the courts decided that TWX wasn't fair, and forced Ma Bell to
sell it to Western Union. WU integrated TWX and TELEX into a single
direct-dial network, although Ma Bell continued to provide switching
for several years.

AFTER TWX was sold, Ma Bell offered Dataphone service, i.e., the
capability to connect teletypes directly to phone lines and to dial
other machines. It wasn't a copy of the TWX network, since there was
no directory of customers, no TWX operator or 411 service,
etc. Dataphone was intended for customers who didn't want to pay
Western Union for TWX, but needed only to communicate with branch
offices or other firms they already did business with.

AFAIK, TWX _always_ used modems, no matter which speed a customer's
machine used. TELEX _never_ used them.

YMMV. Authoritative references welcome.

Bill Horne
Temporary Moderator

(Please put [Telecom] at the end of the subject line of your post, or
I may never see it. Thanks!)


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