Media for History AT&T early modem developments? [telecom]

History AT&T early modem developments? [telecom]

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!