A Brief History of Modems 249
Ant points out this two-page TechRadar article about the history of modems; the photographs of some behemoth old modems might give you new respect for just how much is packed into modern wireless devices.
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A Brief History of Modems
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Always draw your curves, then plot your reading.
Brings back memories (Score:5, Interesting)
I have mod points to burn but I have to post in here.
The traffic system I worked on had 300 baud modems attached to cheap leased lines (soldered in, mostly). Two modems per card. 8 cards on a bytecraft backplane. Up to 128 modems on a 19 inch rack. Each modem had three LEDs (carrier, TX, RX) and at the speed the system operated you could see the poll/response from the regional controller to the sites and back. In the dark it was a thing of beauty. Computers of old.
If something was wrong in the logic (say a checksum mismatch) then you could see it in the LEDs because one channel (slot) would not follow the nice pulse sequence. Several times I mucked up the checksums of a rack and took out a lot of sites. Maybe I shouldn't post about that...
Going back in time my 6502 system had a modem for the cassette interface. I knew you could overclock the UART and FSK modem driver and I had dreams of using my uncles reel to reel hifi system for storage. Never happened. Though I did find that you could use the cassette player as a sound card of sorts by locking on REC and PLAY.
Lady, there ain't nothin' so complicated... (Score:5, Interesting)
In "The African Queen," Katherine Hepburn's character asks Humphrey Bogart's character to make a torpedo. Bogart's character says something to the effect that "Lady, there ain't nothing so complicated as the inside of a torpedo. It's got gyroscopes, compressed air chambers, compensating cylinders..."
I remember once reading details about just how the signals in a 1200 bps modem worked... and modems at higher rates. It was just jaw-dropping how sophisticated it was. The reason why there was a distinction between "bps" and "baud" is that "baud" refers to the number of times per second the signal changes. Well, a 1200 bps modem only changes its signal 600 times a second... but it uses four different combinations of frequency and phase, so each signal combination signals two bits. That's bad enough, but the combinations literally increase exponentially. The 9600 bps modem actually requires the receiver to sense and distinguish sixteen different analog combinations (so that it can encode four bits at a time).
At the time I figured they had to be close to the theoretical limit, which depends on the bandwidth and the noise level. A phone line is only good up to about 3000 Hz. so the 2400 baud rate of a 9600 bps modem is changing about as fast as it can. The rest depends on how noisy the line is.
Theoretically, of course, you can signal at an infinite rate on a perfectly noise-free channel. Just send 3.141592653 volts on the end and measure it with a ten-digit digital voltmeter and, voila! You're sending ten digits at once. Except there aren't any ten-digit voltmeters.
I was frankly flabbergasted when they managed to cram 56 kilobits per second into a phone line. Of course, the 56 kb modems never really ran at that speed--they were always falling back to lower speeds because the phone lines were too noisy. Then they added compression, which didn't do much good because the ZIP files and JPGs you were sending were already compressed. In reality they were trying to cram 56 kilobits of data into a 33 kilobit bag, but it was amazing that it even worked some of the time.
But, lady, there ain't nothin' so complicated as the inside of a modem.
Honebrew (Score:2, Interesting)
It's sad that only commercial modems are mentioned.
I well remember building a series of homemade modems starting in the early '80s.
There were many magazine articles for homebrew modems. Most of these derived from the FSK radio modems in widespread use by Hams at the time.
What!? No mention of AppleCat? (Score:1, Interesting)
The coolest modem of all time, and not even an honorable mention!?
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
Yeah, US ISDN speeds really were (are?) lower, due to RBS compensating for bad signal quality.
See here [wikipedia.org] for details.
Baud vs bps (Score:4, Interesting)
No MODEM using the standards indicated has worked at any speed greater than 2400 baud. (That means 2400 transitions per second).
Many MODEMs work at 4800, 9600, 14400, 56000 bps (bits per second, or pieces of digital information per second).
What the MODEMs have done is use the ability to deliver multiple bits per such transition using FSK, QFSK,QAM, etc.
MODEMs at 2400baud or less did not require flow control -- they worked at serial line speed, and did not buffer. Modems at 4800bps and higher did buffering and would do various flow-control techniques.
Original MODEMs didn't start at 150baud, they started at 75baud, but lazy authors write lazy articles.
The acoustic-coupler worked great at 300baud (TI Silent 700), miserably at 600baud, and terribly at 1200baud.
Still this technology made itself obsolete. People were tying up VOICE channels on the PSTN switches and Telcos hated it, so they created DSL to take data off the voice channels.
E
P.S. The word MODEM (as the article indicates) represents MOdulatorDEModulator. Hence it should be capitalized. This is also try of enCOderDECoder (CODEC). Slightly less related yet as correct LASER and RADAR....
A few things missing there (Score:3, Interesting)
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
Heck, I was using "56K" dialup until earlier this year. Even though it was 33,600. For most things I was doing, it was plenty fast enough. Only thing that killed it was OS X software updates, and the occasional twit who forgot that email is a *text* medium.
Brett
US Robotics (Score:3, Interesting)
For years, Hayes ended press releases with +++ATH0 (Score:5, Interesting)
Its a shame that the article missed so much....
Like the times when much of the industry didn't want to license the Hetherington Patent from Hayes on the "guard time" surrounding the "+++" in the escape sequence, so Hayes ended all of their press releases with +++ATH0 (which would cause a lot of modems to hang up on the BBS systems of their day).
They also missed the interesting fact that the "56K" modem was an old idea that was rattling around Bellcore for years before 1996 and fairly common knowledge in the Bell system. [The big issue with getting there was the need to have digital trunks connecting all of the dial-in server pools with the telephone network.]
Probable never would have become a mainstream consumer device without AOL. Until AOL, you really had to be a geek to use one.
And, of course, the modem wars of 1996-1998, as the major technology companies duked it out, the vast majority of modem companies went bust, including Hayes.
Could you tell speed and error correction by ear? (Score:4, Interesting)
After thousands of times listening to my various modems connecting from 300bps to 56K and with the various incarnations of error correction I was eventually able to knowing how fast I was connected by sound alone. The problem was that as modems got faster and more sophisticated the connection time kept getting longer and longer. Sometimes I'd have to wait through 45 seconds or more of whistles, grinds and groans before the two modem would train. Ah, the good old days.
In the vain hope that they'll have nostalgia value someday I still have in my possession:
1) Mint condition Hayes Smartmodem 2400. The original workhorse.
2) Practical Peripherals 14.4K. long box with a one-line LCD that displays the connection speed and error correction mode
3) US Robotics 56K Courier - The last great standard.
Re:Acoustic coupler era and POTS! (Score:4, Interesting)
If you have multiple PRIs, you can run NFAS (Non-facility associated signalling). You run 24B+0D on all but a handful of circuits, 23B+1D on those. The D channel carries enough signalling for call setup & tear down on all the PRIs in the NFAS group. That way, you're gaining an extra B channel per circuit.
Re:Written by someone born in the 90s? (Score:3, Interesting)
You recall incorrectly. First of all, there can only be a single digital-to-analog conversion anywhere on the line for 56k to work, otherwise there's too much noise and you'll fall back to 33.6. The only way for 56k to work is if the ISP end is all digital - the signal comes in on a T1 line, and the modems are all digital. Secondly, 56k is only 56k downstream; uploading is still limited to 33.6 - so if you could connect two modems on a phone line that was clean enough for 56k to work, you couldn't download faster than the other modem could upload anyway. The digital modems used by ISPs are reversed, of course.
Somebody correct me if I'm wrong about any of this. :-)
Modems are hard to come by now (Score:3, Interesting)
I was trying to put together an inexpensive homebrew computer-to-transceiver audio interface for digital radio transmissions and needed a pair of audio frequency transformers. I knew that all POTS line modems had a transformer in them that would work and I thought that this would be a cheap source for parts that cost about ten bucks apiece new. Of course, I had just recently sent all my old modems to the recycler so I started asking around to see if anyone had a modem that they wanted to get rid of. Out of the more than 20 people I asked, not a single person still had one.
Hard to believe that only ten years ago the modem ruled supreme when it came to Internet access. Now you can't even find one to cannibalize.
KJ6BSO
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
One of the better innovations with modems, but one that was not heralded much was MNP3. MNP5 is a superset and offered compression which helped things, but MNP3 dealt away with the aggravation of line noise, and this by itself made a lot of difference in file transfers.
ISDN did dent modem sales, but at the time in the mid 1990s, ISDN was fairly expensive (about $150-$300 a month.) However, it had the advantage of very low latency. Modems (and mom/pop ISPs) really didn't die off until cable and DSL connections became both widespread and decently inexpensive.
Ironically in the US, modems have not been driven away completely. There are still plenty of areas that do not have cable or DSL access. Sometimes using a cellular "modem" [1] provides a solution, but sometimes that doesn't work (especially in hilly areas). Also, some people just don't do much with broadband, so they have downgraded to dialup because it is cheap.
[1]: Technically it isn't a modem, but a CSU/DSU. However, most people call the USB devices that plug into a laptop modems, even though they do no analog modulation or demodulation.
Re:Acoustic coupler era and POTS! (Score:4, Interesting)
n the mid-90s, we got BRI (ISDN, 2*64 kbps in most of the world, 2*56 kbps in the US). Which pretty much ended the modem era, except for in the US and UK, where 56 kbps POTS modems reigned supreme until well after the millennium.
When the U.S operating companies started rolling out ISDN, I thought all my connection issues were history. But OCs still thought of themselves as regulated monopolies (they still do, really) and got the FCC to set high per-minute rates for ISDN usage — which pretty much destroyed any chance of ISDN being widely adopted. So we were stuck with the damn modems until DSL allowed us to sidestep the federal tariffs. And we still haven't caught up.
I might be misremembering, but I'm pretty sure that US ISDN also had 64 kbps data ports. The 56 kbps limit was imposed on modems because the FCC experts thought that analog connections needed a safety margin to prevent crosstalk.
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
No mention of Telebit? (Score:3, Interesting)
What history of modems completely skips the Telebit Trailblazer? Roughly 18 kbps in 1985 - many years before 14.4k modems became common. Expensive enough to be out of reach of most BBS'ers, though. But worth the money if you were doing UUCP over a long distance call every night.
Re:Lady, there ain't nothin' so complicated... (Score:2, Interesting)
Missed the whole USR Courier saga (Score:3, Interesting)
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
I must be getting old. I still think in terms of, "acoustic couplers... 6502's... that was a few years ago." Doesn't seem that long ago really. Now maybe most people reading this weren't *born* yet at the time.
Soon enough though folks like us will die off, and there will be a generation which has always been connected - nonstop, rather than having to dial things up, doesn't remember the mainframe days, and thinks a 386 is an old CPU. I suppose it's the way of things. Doesn't make me feel any younger though! But what certainly seems true is that a much lower percentage of people now know the nuts and bolts of how things work. I attribute this to several things:
(1) It's harder to *get at* the nuts an bolts now- there are far more layers of abstraction in the way.
(2) Back in the 70's and much of the 80's, home computers were owned by hobbyists, not Joe Sixpack, so most people involved were inclined towards curiosity about how shit worked. Now there still some - more on an absolute scale, but fewer percentage wise.
(3) Now it's possible to use a computer without knowing anything theoretical. Back then, it was not, so it was required that people were technical.
It's not a bad thing generally, and I'm glad so much of humanity is now connected, but there *was* something lost as well (Eternal September, loss of the original net culture, spam, widespread abuse of various protocols, a trend towards a computing monoculture...).
Re:Acoustic coupler era and POTS! (Score:2, Interesting)
And 33.6. I had a 33.6 modem and I swear it provided better latency than any 56k modem I used afterwards. The other thing I hated about 56k modems is that they were only 56k down, not up; a 33.6 could do 33.6 bi-directional whereas a 56k could do 56k down or 28.8k bidirectional, or something like that. All I know is uploading anything significant on a 56k would kill download speed. My 33.6 was much more consistent, even if it couldn't achieve the hallowed 7kBps download.
Oh yeah, there was also the whole V.FC vs v.34 thing on the 28.8/33.6 modems, where basically, V.FC sucked.
Re:Some of the Baby Bells (Score:3, Interesting)
Yeah here Telecom Australia charged $10000 AU dollars per year for a DDS connection (thats 9600 bits per second, serial on a 25 pin D connector, point to point). Its a good service, but 10 grand?. The early limitations on modems not provided by Telstra were basically there to protect that business.
My Modem Story (Score:5, Interesting)
I once worked at a place that had a DEC/VAX mini with a bank of about 8 modems for VT100-compatible terminals. If there were modem complaints such as dial-in problems, I had to first figure out which modem was connected to which phone number. Others didn't always keep the map up-to-date. Plus, it used busy-roll-over.
The test phone was a ways away from the modem bank for the VAX minicomputer, so I had to keep the modem trying to connect long enough until I got there to see which modem answered the call (via LED). The only easy way I found to do this was to manually whistle an acceptable modem tone into the phone in order to trick the modem into thinking I was a modem trying to connect. This would keep it trying long enough to allow me to run from the test phone to the modem bank. It had to be the right pitch and wavering to work most of the time. I got pretty good at it after a while. I learned to "speak modem" a bit.
A computer-room technician once saw me whistling modem sounds into the phone and running back and forth. I later told him why, and he told me I was nuts and mumbled something about whistling sweat nothings to my robotic girlfriends.
Re:For years, Hayes ended press releases with +++A (Score:5, Interesting)
This is how I remember it. Hayes modems, using the patent, required a certain amount of delay time surrounding "+++", their escape sequence, before the modem would recognize it. Thus, "+++" in the text stream wouldn't trigger it under normal circumstances because it would come and go too fast.
But the patent was a patent on the delay; and to avoid paying for the "delay" royalties, other modem companies would just use "+++" without the delay for their escape sequence, which risks modem confusion if accidentally sent as text, but otherwise wasn't that common. However, to embarrass non-patent modem companies, Hayes embedded "+++ATH0" in their digital documents. This would cause non-Hayes modems hang up if they ever transferred such documents. The trick sounds rather Microsoftian.
I remember other vendors complaining to the press, saying "you cannot patent pauses. Next they'll patent Ummm's" or something like that. (Obama would have a big bill if they did.)
Re:Oh, for the "good old days" (Score:3, Interesting)
We all agreed that in a way, it is almost a shame that kids today are growing up with remarkably better technology than we had at their age (and it hasn't been that long ago that we were their age). We all sort of miss dealing with cobbled together and salvaged parts, trying to eek out any performance we could from our machines. One of the friends present recalled helping me overclock my 33 mhz machine to 36 mhz (woohooo! A 10% gain) and how excited we were.
Here's a fun factoid* for you: most electronic parts have an error tolerance of at least 1%, with 10% not unusual. Even things like the clock source of a PC would probably drift by about 0.1% due to things like humidity, temperature, or whatever. Or to put it another way, a modern 3GHz CPU running at a "fixed speed" loses or gains about 3MHz from the influence of the weather. Given that most modern CPUs do a lot more "work" per clock than old XT era processors, that means that just random variations in the performance of my current CPU account for more processor power gained or lost than my first 2 computers combined.
The next processor I'm buying will have more on-chip cache than the total system memory of my first 3 computers combined, and will be bigger than the capacity of my first hard drive!
But on the topic of modems, around the start of the 56K era, I signed up for some random 'beta tester' program with Netgear through work (summer internship during high school), and I got sent a $1000 "enterprise" modem to beta test. It looked and worked like an ordinary 56K modem, but had very good quality components, and very good noise resistance and reliability. It was one of the best electronic devices I had ever owned. It had amazingly low latency, and was the best for playing games online. It outperformed the latency of the first-generation cable internet here in Australia for years.
*) May not be actually factual, this all depends on the technology used to generate the clock, some are more accurate than others.
Comment removed (Score:3, Interesting)
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
Ahh, and not only exciting, but would only later be known as 'epic'. My first foray into the internet was on our school library's VT100 terminals which were primarily used for queuing up inter-library loan requests. This was in 1995. Getting Mortal Kombat cheat codes and fatalities was never so easy. I also remember printing off the Duke Nukem 3D build editor docs on that same machine, but I think that was a bit later on. Shortly after my church confirmation class took a trip to a ''church'' college which had machines which displayed the WWW in all its graphical glory. They were running Netscape (probably 2.0 or 3.0, I didn't bother to check at the time). I was smitten. Not long after that, our town got local dialup access, and at age 15 I convinced my mom to let me pay for and install a second phone line for it. I soon learned enough HTML and Javascript to 'hack' the Perl/CGI chat room I used to fool around in -- giving myself full administrative ability. W00t! The coolest damned thing I ever did was play my chatroom buddy in Quake II -- ON THE INTERNET!
To this day, there is nothing more exciting than hearing that 14.4 modem chirp off the connection sequence. Sometimes I kinda wish my DSL connection made that same noise. I'll always treasure those halcyon days. Thank you, Mr. modem inventors. Mine served me well far longer than it should have, mostly reliably, and is the singlemost important reason I ever became a computer geek. Thanks a million! Now who is calling me at five in the morn--
-AT++[NO CARRIER]
Bah, kids nowdays -- 42bps modems (Score:4, Interesting)
Bah, kids nowdays, so spoiled with the megabit modems.
Before the Bell System modems, there were over-the-airwaves modems, going back to 1930 or so. The endpoints were teletype machines, whirring away furiously at 60WPM, 7.42 bits per character. ( 5 data bits, one start bit, 1.42 stop bits).
The modems wee made up of L/C filters and a trunkful of vacuum tubes. I used to have a military modem, a CVV -something, that was the size of a suitcase and weighed about 60 pounds. 42 BPS.
But it could do 42BPS over a noisy fading shortwave radio link, all day long, while taking direct mortar rounds, and never say "NO CARRIER."
Re:Acoustic coupler era and POTS! (Score:2, Interesting)
I developed a 300 baud modem for the (then) brand new RCA data terminal back around 1980. The trickiest part of this thing was that the filters had to be designed and made from discrete components.
The plant manager saw my design which had precision components and he had a fit. His instructions were, "Use the components we have in the stock room". He also saw the line transformer and he said, "This is the age of semiconductors, get rid of that transformer".
I spent weeks researching how to replace that transformer with a semiconductor device that wouldn't distort the signal, operate bilaterally (in and out), and withstand the the 10,000 volt pulse that the FCC required for testing. I finally found such a beast, so I gave the manager a choice... Use the 6 cent transformer, or replace it with a $40 semiconductor.
My complaints about using non-precision components fell on deaf ears, so I figured the only way to prove that this wouldn't work would be to build a prototype and show that it would fail. To my dismay the first prototype worked flawlessly. I was told to build 10 more for FCC testing but not a single one of these worked even though the frequency response curves were all on the mark. I finally discovered that the phase response was a mess. I finally convinced them to use precision components.
Re:Acoustic coupler era and POTS! (Score:1, Interesting)
Something doesn't agree with my experience here.
In the late 1990's, I had a dedicated dual channel ISDN line to my ISP. For a few months after it was installed, things were great - I had all 64k of both channels. Then, I noticed performance issues. Further inspection noted that at some times, ONE of the channels would drop to 56K... at other times, BOTH channels would drop to 56k. Yet other times, they both had 64k.
After exhaustive dialog between the phone company and ISP, the phone company found that a trunk line between the ISP's long distance provider and my phone company was almost at capacity (64 channels of 64k each). When the line got filled to capacity, my ISDN call got routed to a voice-only trunk line, the channels of which were limited to 56k.
So yeah, I'm in the US (Ohio) and I did get full 64k on my ISDN line.
Re:Acoustic coupler era and POTS! (Score:5, Interesting)
For that matter, I guess it's more than just technology. Almost none of the kids graduating with my nephew know how to fix a leaking faucet, grow a tomato, or change the oil in their car. Hell, two thirds of them can't even cook rice.
I can't help but feel that we've lost something valuable.
Re:Acoustic coupler era and POTS! (Score:2, Interesting)