The history of private datacommunication 4280

Correct.

Of course *long* before that there were a number of others developed. Teletype machines replaced manual telegraphy, and as various forms of Frequency Division Multiplex became common (but in particular the J, K, L and N carrier systems from WECo) it was also necessary to convert Teletype's DC circuits to use voice channels for long distances.

In the 1930's the 40C2 telegraph system came into use. It placed 17 telegraph channels on one FDM voice channel, and required about 16" inches of rack space per channel. In the early 1950's the 43A1 system replace that, and required only 14" inches of rack space for 3 channels. That was replaced in the 1960's with the 43B1 system, which took up only 36" inches of rack space for all 17 channels. Those of course were all electron tube type equipment. In the late 60's and 70's transistorized equivalents were used (the examples that I know of were all made by Lenkurt, rather than WECo, and were the 23A1 and 25D telegraph systems).

In the 1980's things like stat mux (Infotron?) became common too, and basically data comm was not only for computers, but was in fact controlled by computers.

IBM may have invented "a modem", but did not hardly invent the concept of a modem. Radio Teletype modems were quite common during WWII. All of the various "modems" were just extensions of the Teletype "Terminal Unit" designs (40C2 et al mentioned above) that were being used to provide long distance telegraph lines.

That is true, but it would be hard to claim it was much of an innovation in respect to modem communications. It was, in respect to switched data networking, very innovative.

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