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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 vux984 on Wednesday November 22, @12:46AM

    by vux984 (5045) on Wednesday November 22, @12:46AM (#1333807)

    /shrug; it was 25+ years ago; I'm likely mis-remembering a few details. I accept your correction.

    Not that I expect it makes any difference, but this was in Canada. I do definitely remember reliably getting more than 33.6 on them though - at least at some point in their life. I also recall doing the v.92 or some other upgrade on them too.

    And I definitely recall that we started with the modems paired in hub-spoke; with one spoke connected outwards one more time (due to the long distance zoning -- it was a long distance call from the furthest branch to head office, but everything was local if we did that hop); we were using Apple SE30s doing Appletalk routing over the modem pairs at the start.

    But it IS possible they never got above 33.6 though in that original configuration, I really don't recall.

    Its entirely likely switched to dialup internet; instead of direct dialing from one to the other; before moving to ADSL, which would have opened up the likelihood that the ISP side was digital for a time.

    Eventually they'd all been retired in favor of ADSL.; although I recall ADSL took forever to be available at one site, so we went with ISDN there for several years.

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