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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, Informative) by drussell on Tuesday November 21, @02:49AM

    by drussell (2678) on Tuesday November 21, @02:49AM (#1333680) Journal

    I was literally in support for a year or two during the 56k dial-up era, and I don't think I ever had a customer report a 56k connect, and I know I never saw one in real life.

    I literally ran a BBS in the '80s and a small ISP from the early dial-up days in the 90s all the way to the present day with various last-mile "solutions." From Paradyne to Mimosa... 😀

    Over those years I have run virtually every model level variant of USR Courier ever made (except for the original 9600-only HST; my very first SysOp program Courier was shipped as a 14,400 but field upgraded to 16,800, I never had one of the rare 9600-only models, though several of the other local SysOps in the local 1:134 FidoNet and SASA did...) on the analog end of the system and then digital ISDN BRIs, once that was really "a thing." Even dabbled in PRIs for a brief time. Yikes.

    There was/is NO SUCH THING as 56000 over the actual phone system in North America unless your telco had/has their equipment configured outside FCC / CRTC spec, which I don't think was ever actually "a thing." You could get 53333, and most of my customers in the dial-up ISP days that were close-ish to their CO would consistently get that full rate, 52000 or 50666. All squarely 5k/sec, which was "full blast" at the time. Most others could get 44000-49333 if they could get a digital connection. Otherwise it was 31200 or 33600 maximum, obviously. If you were unlucky enough to be on a Tadiran Pairgain splitter, you were out of luck beyond 26400 or perhaps 28800. Often only 21600. Those things SUCKED.

    You were lucky to get something like 44k, 46k, etc. I'm sure *somebody* got one in the lab, maybe even in some area with remarkable clear phone lines? I just know I never saw one.

    It was limited by the FCC regulations to 53333. Of course you never saw speeds of 54666 or 56000 in the field, since they were disallowed. 🙄

    44000/45333/46666 are actually pretty good speeds in some areas, though if your customers could consistently get that, they could probably manage to boost it to 48000, 49333 maybe even 50666 just by finessing the customer's premise wiring. Same idea as when provisioning for ADSL, (except not worried about high frequency per se,) but same ideas, run proper twisted pair all the way to the modem, eliminate extra connection blocks, random crappy untwisted parallel-wire line cords, extensions, bad chinesium phones, etc. and you could often easily boost a customers' average speed a couple levels just with simple shit done right... The telcos will often leave super bad bodge wiring EVEN UPSTREAM OF THE DMARC point unless you ride them and complain.... but I digress....

    If you're 10 km from the rural wirecentre, you're probably still screwed... :)

    It could be that those people lived in some kind of magic bubble where they never had to call support for anything; but modems are just one aspect of it. If your browser is having issues, you won't mention your 56k connect so there's a reporting bias there. Still though, you'd think I'd have seen one or known some people that actually got one. Nobody did.

    Right, nobody did because full 56k isn't actually allowed to be a thing on the real, physical phone system. 😉 53333 sure was, though... Most of my customers could get ~5kbps.

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