When traditional dial-up modems communicate, they encode digital bits as screechy analog tones that would then be carried over phone lines originally designed for human voices. It’s an imperfect way of doing things, but it was the most practical way of networking computers in the olden days. There was already a telephone line in just about every house and business, so it made sense to use them as a conduit to get computers online.
For years, speeds ticked up as modem manufacturers ratified new, faster modulation schemes. Speeds eventually reached 33.6 kbps which was believed to be near the theoretical maximum speed possible over standard telephone lines. This largely came down to the Shannon limit of typical phone lines—basically, with the amount of noise on a given line, and viable error correcting methods, there was a maximum speed at which data could reliably be transferred.
In the late 1990s, though, everything changed. 56 kbps modems started flooding the market as rival manufacturers vied to have the fastest, most capable product on offer. The speed limits had been smashed. The answer lay not in breaking Shannon’s Law, but in exploiting a fundamental change that had quietly transformed the telephone network without the public ever noticing.
I worked on a isdn product in the early 90’s. Isdn could have been an easy stop gap between analog and fiber but Telcos had made isdn impossibly convoluted. Later when I ran an isp we had ~10,000 analog customers and maybe 20 isdn.
I’ll have to see if I can dig it up, but there was an article I read a good while back that’s basically the long-form version of your comment. Something about ISDN being the stepping stone to broadband that never was.
The gist was that those who could get ISDN early-on loved it, but for anyone else, it was too little too late as DSL was starting to be rolled out.
I lived in the boonies throughout the dial-up era and had BoonieNet as my dialup ISP (couldn’t even use AOL since every point of presence was long distance for us). Sadly, 33.6 was peak performance in my area, though more often, it was 26.4 Kbps due to our distance from the CO and crappy lines.
What I learned from this article is that the CO definitely wasn’t using any kind of digital trunk at the time since even people in town right next to it never got faster than 33.6.
