I hate to disagree with our esteemed moderator, but at least into the late 1950s and probably into the 1960s, [TWX] was a manual service on regular DC telegraph grade channels.
The TWX operater answered (by keyboard) with GA.
The caller responded by typing on the keyboard the desired number. The company I was working for by then had two numbers in New York. The numbers were NY 1-1 and NY 1-1847. The operator would connect with the distant operator, who would reply NY. The operator at the originating end then would type the desired number and the distant operator would connect with the number, probably in a jack field. If it was busy the distance operator would so report by keyboard. The two numbers were not rotary. If the first one was reported busy, then you had to type in TRY NY 1-1847 or some similar statement.
Only New York had prefixes...as I recall, 1 was Manhattan and the other boroughs had 2, 3, 4 etc. Numbers in other cities were just numbers of variable length.
I know the TWX network was switched over later to dial operation, but certainly in those earlier years there were not sufficient voice grade circuits to make such wasteful use of them. About the same time the use of dial-up modems was becoming fairly common, first at 300 bps.
An earlier [post] mentioned various brands of modems, but left out the one that pretty well defined the basic protocols that I think are still used today -- Hayes.
Wes Leatherock snipped-for-privacy@yahoo.com snipped-for-privacy@aol.com
***** Moderator's Note *****Wes, thanks for setting the record straight. That's what I deserve for assuming that I know everything. ;-)
Perhaps you can confirm something: an old AT&T tech told me that before N carrier was introduced, toll cables were so precious that it was common to use duplex/simplex repeating coils to make Ghost circuits from phantom circuits, and to obtain "Wraith" circuits from Ghosts. He told me the Wraiths carried telegraph traffic, sometimes working against ground and sometimes via other Wraith circuits, and that testmen had to know American Morse code because the testboards used Morse sounders and keys for communications between offices. True?
BTW, I sometimes use a TDD myself, and the convention is _still_ to use "GA" at end of each transmission. It's funny how conventions hang on from generation to generation: ham operators send the "prosign" SK at the end of their contacts, and if you look at the dot-dash pattern, you'll see that it's the same as the "-30-" that newspaper reporters used to put at the end of their telegraph dispatches when they were sent with American Morse code.
I used to own a Model 15 teletype, which I used for Ham radio. They weren't called "bronze beheamoths" for nothing: that machine would run forever, but it took two men and a boy to lift one. I don't know where they all went: my dad put mine out for the trash collector when I was in Vietnam, but so many were made that I'm surprised they're so rare now.
This has been a great thread: I had forgotten the difference between holding and pulling magnets, and that Model 15's sometimes had a polar relay in them, and even the tuning forks used to set their speed in the field. GIYF.
Bill Horne Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or I may never see it. Thanks!)