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56k modems relied on digital trunk lines


If you came of age in the 1990s, you’ll remember the unmistakable auditory handshake of an analog modem negotiating its connection via the plain old telephone system. That cacophony of screec…

Credit: , CC BY-SA 4.0When 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. 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. Line quality and a user’s distance from the central office could degrade performance, and power limits mandated by government regulations made 53 kbps a more realistic peak speed in practice.

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56k modems

Photo of digital phone lines

digital phone lines