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

https://www.10stripe.com/articles/why-is-56k-the-fastest-dialup-modem-speed.php

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: 4, Interesting) by Mojibake Tengu on Tuesday November 21, @12:19AM (1 child)

    by Mojibake Tengu (8598) on Tuesday November 21, @12:19AM (#1333673) Journal

    The modem link protocols used statistic compression since MNP5, so the port speed at double of connect speed was a necessity.

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  • (Score: 2) by drussell on Tuesday November 21, @04:23AM

    by drussell (2678) on Tuesday November 21, @04:23AM (#1333690) Journal

    Even more than double. Even MNP5 could do over 2x compression on many payloads.

    Does anyone remember the name of the terminal program software that did MNP in software on a regular modem, like in the 2400 bps days?

    The default color scheme was a mostly dark blue, but I can't remember for the life of me what the name was or what company was the author... ?? Had a big blocky title screen with white lettering, IIRC.

    It WASN'T Microcom, I think somebody might have reverse engineered it (MNP), probably got tied up in court with Microcom and the product eventually vaporized, everyone involved probably subsequently tried to pretend it had never even existed... ??

    I had a bootleg copy from whoknowswhere, back in the day. It was pretty cool, and I used it for a brief time for certain purposes dialing up other BBSes before I bought my first HST on the SysOp program from USR. It WAS cool, in that the serial port rate didn't matter since the MNP was being done in software on the PC side! It really was the bees knees! :)