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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 drussell on Tuesday November 21, @03:01PM (1 child)

    by drussell (2678) on Tuesday November 21, @03:01PM (#1333735) Journal

    Alright, I stand corrected then. Touché, sir! :)

    Ignore my sassy comment if you really were on dialup when you posted that. Kudos!

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  • (Score: 2) by Hyperturtle on Wednesday November 22, @06:58PM

    by Hyperturtle (2824) on Wednesday November 22, @06:58PM (#1333883)

    It's funny, I just cleaned my office closet and pulled out two external US Robotics HST Dual Standard 16.8Kbps modems with the upgrade daughterboard to bring them into complince with the 56K standard for v.92 (no x2 or rockwell pre-standard stuff).

    Those modems were not cheap when I bought them, and the daughterboard upgrades were also not cheap...

    Anyway I never used Windows 95 with them, but I did use them with DOS and terminal emulators and so on.

    I had to lock the com ports to 115,200 or greater in order to hope to see 53.3Kbps down and 33.6kbps up. I got the best connections on an analog line dialing into an ISDN line, which, despite the differences, provided a bit of a cleaner connection on the far end. I heard of people getting 56K down on an analog lone connecting to a single channel of ISDN like that, but I was never so fortunate to *connect* at that speed. It might have auto-negotiated during the call, though, to that higher tier--there was no real user feedback to indicate that this happened, but it was possible.

    Truly a great improvement over 16.8kbps, which was glorious in its own right.

    I also have two US Robotics modems that had a dedicated side channel for voip. It allowed me and a friend (who borrowed the other modem so we could call each other with it) to talk on the same phone line that we were using to deathmatch each other in Doom with. Later, I set up a quake server with a network connection to other PCs, and he could dial into the server, I could be on the phone with him, and we could have other players in Quake at the same time -- although only he and I could voice "chat" like that.

    It used 9600bps of the connection bandwidth for the voice. That means if the connection was poor, the call quality was as well. Also, you could disable that function and just use the modem for the data throughput it had. It generally connected at 33.6kbps under most conditions; it wasn't as speedy as the Courier modems.

    The same friend later gave me the modem back when he upgraded his 9600bps sporster to a higher speed one via a switcheroo -- as it happens, the physical shells of the sporster modems were all identical starting with the 2400bps MNP5 external models... so if one found an old 2400 baud sportster external modem at a computer/ham radio show, and if one was so inclined, you could particpate in the clandestine upgrade program found via retail channels called "swap and replace". Not that I know anything about that! (I already wasted my money on high end Couriers, boo-hoo...)

    Anyway the fine article angered me. No one chose 56K as the speed because of some magic variable due to it not being binary or decimal. It was because phone lines sucked for data and that was about as much blood as could be squeezed from the stone with the technology of the day!

    Now, aside from the win95 user... I didn't think it was even possible to make such a high speed connection anymore due to other technological advances.

    I kept my modems so I could make calls to places I supported when I had a power outage here--laptop and phone line would still work even if the power was out. However, when AT&T upgraded their backend to fiber and thus voip, they put a quality of service cap on the analog emulation so that way fax machines could connect at 14.4kbps at best -- I've seen as low as 9600, which businesses having to request a higher cap to allow for dedicated "analog" lines in their PBX to be allowed 14.4kbps.

    In what feels really retro and like audiophile purism talking about vacuum tube types, the signaling was clipped at the edges and the warmth of the analog carrier connection was turned cold, so to speak. Only a certain frequency range was guaranteed and sometimes that was even just an up to* promise.

    That still had to fight with the quality of the wiring; if it was an old building (or an old house) you might have had a better connection than 14.4kbps (like 21.6kbps was really common even when 28.8kbps was standard) but it got ruined because the noise preventing a better connection was poorly emulated on the fiber backend as digital noise and... I ended up getting cable for my internet and a UPS to provide uptime.

    I once used a cell phone to play Information Society's 300 8-N-1 into a land line answering the call with a modem, and it worked (if perhaps 300bps is still within reason to ask for over a cellular connection). For the unaware, its a recording, so its easier to get a connection than a dynamic negotiation. It's too bad its such a pain to get a 25-pin serial to USB connection going on modern cell phone hardware... it'd be a fun way to change the defaults for some chatty applications network bandwidth use, but maybe my definition of fun is weird.

    (Dr Russell I think we are distant kin as a result of your professed knowledge. I would deathmatch you in something, but ever since my mom came close to killing me about crazy dial-up toll charges... I have been reluctant to dial out of my calling area...even though its been 20something years...)