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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: 3, Interesting) by jman on Tuesday November 21, @01:23PM

    by jman (6085) Subscriber Badge on Tuesday November 21, @01:23PM (#1333724) Homepage
    Nice write-up. Reminded me of a buddy, Phil, in Houston, who ran the Breeze BBS back in the 80's. He spent his retirement (both time and moolah) renting phone lines and buying USR Courier 14.4's. I volunteered coaxing the 286 boxes he had into handling more and more users, but at home had to do with a fancy 1200 baud model (so much better than 300!)

    In the mid-60's, living in hometown Chicago, our upstairs neighbor worked at the main ATT switch. One day he took me on a tour. Miles of wiring, what looked like two-story racks of spaghetti everywhere. (OK, very well organized spaghetti.)

    We were somewhere in the basement, and he showed me this thing, lit up under glass, that looked to be a piece of cable around the thickness of my then 5-year-old arm.

    He asked, "Know what this is?", then went on, "it's the future. Something we've been working on called 'Fiber Optic Cable'.

    Don't even have copper connected to the house anymore. These days I take my (potentially) 1G pipe for granted!
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