15. Oktober 2017

The Speaking Modem

This is an old story. To be honest, I don’t recall details any more, not even the exact circumstances. Researching I read that telephone modems had been officially introduced in Germany in 1966 as Übertragungsmodem D 1200 S (“transmission modem”); S meant serial.
ESK relay, see https://de.wikipedia.org/wiki/ESK-Relais
   At that time I studied Electrical Engineeing in West Berlin. Computer Science hadn’t been in­ven­ted yet. After having soldered over thou­sand little ESK (Edelmetall-Schnellschaltekontakt-Relais) relais into a system to register phone calls I switched to software.
   A later model was the Einheits-Postmodem (“standard postal modem”) D 200 S. Here you see a “D200S 03” with the handwritten remark “300 Baud”*), sized about 60 cm × 30 cm × 20 cm – 60 cm being today’s standard dishwasher size. The 200 and 300 baud came from an extra hardware plugin to clock for a then asynchronous transmission.
To dial in as human you didn’t want synchronous transmission. You must have had asynchronous traffic, as you type character by character with your human ten digit’s (finger’s) irregular timing. And you needed duplex traffic, so as to get achnowleged what you typed character by character. The speed of just up to 30 cps, characters per second, sufficed fully. Your teletype could print just 10 cps.
Harald Schummy, Signalübertragung, p 350, 2013
*) Don’t look up Baud in Wikipedia. For us it used to be roughly equal to bits per second, bps or b/s. An asynchronous byte having ten bits (start, 7 data plus one parity or 8 data bits, stop) 100 baud meant 10 characters per second, 10 cps or 10 Byte/s.

That said, here comes the story. The Technical University of Berlin’s mainframe ICL 1904 back in in 1968, when we were allowed to use it at night, had a dial-in modem. I’m 80 percent sure. If that’s wrong you must transpose this story to the time of time sharing Basic systems (60s, 70s) that we supported at HP, or to private mail boxes like Zerberus – which I used – or Fido, both 1984. For more on Berlin’s ICL see my “listening to computer bugs”. – More further down+).
   When you connect an analog modem to a computer you hear strange sounds at the beginning, while the modern modems agree on a mutual speed and transmission type. Of course you can record this sound on a tape recorder.

This recording includes the initial American tone dialing.
We only had pulse dialling at that time, but in principle: That’s the sound – with its optimistic high key ending.
   With the Hayes command M2 you cuuld tell a modem to leave on its loudspeaker. So you heared it doing its job all the time. Our system had a command to the operating system to print a message on the console, like machine room to bridge on a ship. Today that was the Windows net send command. So I could dial up the mainframe from outside, and for example ask the operator to return my phone call. I tape recorded this short digital dialogue.
   Playing back the sound track into a telephone’s microphone – without a local modem attatched – I got the message through equally easy, naturally giving just the one callback number I had recorded. It worked. (Young reader: Ask yourself, why I didn’t I send a SMS?)

For more about “our” ICL 1904 read Listening to Computer Bugs.   
Another story: https://blogabissl.blogspot.com/2017/10/how-i-tried-to-trick-computer.html#retention

Permalink to here: https://blogabissl.blogspot.com/2017/10/the-speaking-modem.html
Link directly to the story:

+) To the ICL 1904 and its modem I get this comment by Brian S.:
   If you are referring to an unsuffixed 1904 with 32KWords, then the machine was most likely to have been running an E4BM Executive (standard executive allowing for 4 programs under operator control). It is possible that an early version of GEORGE might have been used, but in my opinion unlikely. [Yes, I remember, we could run four programs in parallel. fj]
   E4BM (and other basic executives) would not
service communications lines as such, it would see the communications control device (multiplexor or uniplexor) to which the line(s) were connected and would not care whether there was a modem on the line or not (direct in-house connection), that would be on the outside connection(s) of the controller.
   In this era it was more common for the operator to answer the telephone and then switch to data after identifying the caller, but modems could be set to auto-answer (switch/wiring). Incoming calls would on the 'wrong' side of the controller for Executive to see the line answering, as such.
   Any attempt from the terminal to wake the line (break-in), would result in an interrupt being sent from the controller to Executive. If there was no program (or operating system) loaded to control the communications device, Executive would usually respond
line closed. If a communications program was loaded, any input from the communications line(s) would be passed to the program for it to process, one function of which could be to output a message from the terminal on the operators’ console. 
– Thank you, Brian, I think it becomes more probabe that my dictaphone dial-in trick came later … 

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