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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: 2) by dwilson98052 on Wednesday November 22, @01:33AM (1 child)

    by dwilson98052 (17613) on Wednesday November 22, @01:33AM (#1333810)

    ...network engineer at an ISP with 20K customers during the 90s and 56K was more of marketing gimmick for most customers as they rarely saw speeds much over 33.6k.

    Most customers were ok with this, but many would complain and open trouble tickets with us and we'd have to help them get a ticket open with the phone company.

    The biggest issue we had was distance between the user and the CO they were connected to, water intrusion, and mismatched impedance on the lines... in most cases in the early days the phone company wouldn't or couldn't do much to help as long as the line was suitable for voice. After our user base started to grow and we got a better account manager it became a lot easier to get help for customers, but there were still limits to what they could do.

    Funny thing is that when DSL hit the market most of these problem customers couldn't get that either... we managed to get many of them on ISDN connections or even T-1s as the phone company could use what were effectively amplifiers to boost the signal, something they said they couldn't do for pots lines due to regulations, though there was nothing stopping them from using one of the ISDN channels for voice if the customer wanted to give up one of the 2 64K channels. IDSL was a big hit because instead of 128K from the two 64K D channels you also got to use the 16K B channel for data as well........ there was also always connected, no lag time for channels to connect.

    Good times, don't miss it much though

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  • (Score: 3, Informative) by jman on Wednesday November 22, @12:07PM

    by jman (6085) Subscriber Badge on Wednesday November 22, @12:07PM (#1333854) Homepage
    Got an ISDN line in the latter 90's through the local computer club. Seeing the extra wiring, the next door neighbor, a WW II vet, asked me after Bell finished installing the exterior box if I was running a bookie operation.

    Back then, 128K (even if you never really got all of it) was a huge upgrade from a "standard" modem!