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posted by martyb on Monday November 20, @11:02PM   Printer-friendly
from the good-question dept.

If you've ever had dialup internet service, or still do, or just know someone that does, you have probably heard terms like "56k modem". "56k" has become almost synonymous with dialup Internet access. But it's such an arbitrary number. It's not divisible by ten, it's not a power of two... so why was it chosen as the fastest dialup speed? For the answer, we will have to travel back in time quite a while.

Our visitors from Google should be warned that this is not a "stripped down" explanation; it is intended for relatively technical readers. But if you really want to know where this magic number comes from, you need to understand some of the technical background. As we shall see, "56k" was not just pulled out of a hat.

[...] Anyone that has ever used a dialup modem knows full well that they don't actually get to connect at that speed, though. And that their connection speed varies each time they dial in. There are two factors at work here.

The first is the FCC. If you are in the United States, the FCC places a restriction on the power output of devices connected to the phone network. The result is that you will never be able to connect at a speed faster than 53.3 kbit/s.

The second is the overall complexity of the phone network. 56 kbit/s (or 53.3 kbit/s) requires very good operating conditions, as it is really operating beyond the paramaters of what the phone network is required to be capable of. Operating at these speeds requires that there only be one ADC between the user and their ISP (which is not guaranteed to be true, but typically is), and that the copper wiring in the user's "local loop" have very good electrical properties. Part of the dialup process that is used to initiate a connection is an evaluation of the overall quality of the connection; if it is determined to be lacking, the modem will automatically drop down to a lower data rate.

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  • (Score: 2) by Joe Desertrat on Wednesday November 22, @01:34AM

    by Joe Desertrat (2454) on Wednesday November 22, @01:34AM (#1333811)

    Way back when I first got dial-up, I would consistently connect at 48k. It didn't seem to matter which ISP or phone service I used. I moved to a different neighborhood in the same town, and suddenly the fastest I could connect was 31.2k. I don't ever recall any variance from those numbers.

    I ended up getting DSL, and used it for years, but eventually gave it up when AT&T decided they were phasing it out without offering any alternative in my neighborhood (their fiber wasn't ready yet). They led me on for a couple months, it would go out, I would call, it would come back, then a couple days later go out again. I got fed up a lot slower than I should have, and when I called to cancel they offered no argument, only a warning that I couldn't get that service again. Good riddance! I have Spectrum now, much faster at the same price, and despite their reputation I have had no trouble with them. Good thing, as there are no other choices, unless maybe satellite is considered.

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