Why 56k is the fastest dial up modem speed
10stripe.com
10stripe.com
This distinction was getting lost to time even back then with everyone just assuming it was some arbitrary FCC limit. This post from NANOG in 1998 explains it: https://archive.nanog.org/mailinglist/mailarchives/old_archi...
Like channel banks prior to the D4 and a 1AESS would very likely have a marked difference to your speeds.
It couldn’t do it for binary, but it still was noticeable with HTML and email.
It didn’t last long. Whatever accidental phone line + ISP magic enabled it was quickly “fixed”.
but PPP compression wouldnt explain modem reporting faster speed. Btw I never saw PPP compression enabled in the wild either.
Maybe it was PPP instead. It was the effective link speed, not something measured with a download tool.
This would have been ‘97 or so, so my memory is hazy.
I finally installed an ISDN. That was delightful. Not only did it allow me to have two lines - one for voice and one for data - the netgear RT-338 ISDN router automatically dialed my ISP instantaneously. It felt like I was always connected because I didn't have to wait for a modem handshake. Speeds were more than twice as fast as what I could get with my analog modem. However, by far the MOST IMPORTANT thing (and mostly the reason I installed the ISDN in the first place) is that my latency took a nosedive allowing me to become an LPB with a 50ms ping time on QuakeWorld. >:-D
(Shoutout to Charlie S. from OuterNet, Austin's best ISP in the 90's)
Fucking Telstra
Hotline? https://en.wikipedia.org/wiki/Hotline_Communications
I just thought to post this since when I visited in September, some actual retired telecoms engineers were part of the tour group. One had been involved in the development of submarine cable technology.
Out of all of those however, panel is my favorite however, it sounds amazing to listen to, both the equipment and what the line sounds like. A call between a panel and the number 1 xbar sounds amazing, nothing quite sounds like revertive pulse signaling.
Interestingly enough, there were three switches made that used RP internally - Panel, 7A Rotary and 1XBAR - and if you go find video of the 7A Rotary, you'll see it sounds almost exactly like panel, because the unique sounds of the rotary sequence switches both exchanges use.
The robbed-bit signaling thing is really a red herring: it was a problem, but not THE problem. At the time analog 56kbps modems were popular, it was already possible to negotiate 64kbps/8-bit clean DS0 channels over T1 — you just needed a PRI or an inter-machine trunk to do so.
In fact, if you were an ISP at the time, you generally needed those modems connected to T1 PRIs or IMTs anyway to support your ISDN customers economically. (My memory may be getting fuzzy on this, but I also remember that certain access concentrators with k56/v.90 digital modems would only negotiate the higher analog speeds on a PRI or IMT bearer channel.)
What there was absolutely no appetite to do, on the part of the voice carriers, was beef up the bandwidth available on POTS lines by developing new ADCs, getting rid of companding, or engaging in labor-intensive “facilities grooming”[0] for a POTS subscriber, in the way they routinely did for T1[1] circuits.
0 - Telcos call their lines and equipment “facilities.” Grooming, in the context of outside plant (telco terminology for the physical cabling that goes to subscribers) means to select wire pairs that exhibit good noise and echo characteristics and to remove elements, like poor splices and bridge taps, that impede performance.
1 - T1s, unless delivered to a customer via an optical transport network, use the same copper lines as analog POTS lines. Originally, T1s required two pairs (four wires). This eventually was replaced with HDSL4 (two pairs, but better distance and repeater characteristics,) then HDSL2 (single pair.) As the names suggest, the encoding used was a DSL variant.
The article didn't talk about modulation schemes and I wish it had.
* Select (or repair) “good” pairs that didn’t have poor echo, impedance, noise, etc. characteristics.
* Not compand the resulting PCM sample with mu/alaw companding.
* Provide an atomic bearer channel from the telephone switch to the ISP that was at least 112kbps.
* Develop a modem encoding scheme that could take advantage of the extra bandwidth.
At this point, you’ve reinvented a really crappy version of DSL that could be user-signaled to call different networks (i.e., phone numbers.)
The other option, the one that people selected, was to use the copper facilities but bypass the phone switch and its associated audio and in-band signaling shenanigans. That was/is xDSL.
Bumping ADC to 16bit will remove some of quantization noise, but still leave you with inherent noise of the transmission medium and power limit (FCC/AT&T).
This is misleading. The phone network used analog links (typically microwave relay) for long distance almost exclusively for many years (into the 80s) after the introduction of T1. T1 itself is not terribly well suited to very long distance links though and can only be pressed into it with repeaters every mile or so.
How do I know? Well, we had a pretty big wildfire a couple years ago that burned a microwave tower a couple hours away. The official response was that they couldn’t get internet back in town until they rebuilt the tower. Our internet was down for a couple weeks until it was safe enough for them to get back to the tower site.
In a very real sense microwave relays are the direct descendant of the optical telegraph (aka "clacks" in Discworld lingo).
Its a radome, used to protect the antenna from weather.
Had "the second longest T1 in the service area" for a while there. BellSouth declined to renew the contract in 2008, the business folded, etc. In 2013 I was digging through the old building, and the T1 line card in the wiring closet was still powered.
Nowadays the relay boxes all the way into town are mostly hanging open or have been repeatedly run over. I wonder how much of the rest of that infrastructure they just abandoned in place.
The reason should be obvious. Digging long distance trenches and all of the property buying/leasing and right of ways/easements and all of the other fun stuff makes it a total nightmare. Radio broadcast just makes much more financial sense as well as logistically.
Those microwave links represent layer 0 in the connection which is by definition always analogue, the same is/was true for T-1 which used alternate mark inversion [1] signalling over a 4-wire circuit. It is the type of signal carried over the link which decides whether it is considered "digital" or "analogue". T-1 carried 24 time-divided PCM channels ("digital"), microwave links could and can carry both frequency-divided multiplexed analogue channels ("analogue") as well as time-divided PCM or packet-switched channels ("digital").
[1] https://en.wikipedia.org/wiki/Bipolar_encoding#Alternate_mar...
Meanwhile, on a random roadtrip through rural Illinois yesterday, I was seeing "5G UC" on my cell phone, out in the middle of nowhere. Unevenly distributed, indeed!
Even if I found one, I would only be able to make a collect call. I never carry loose change on me, and I haven't had a calling card in decades.
Yes
> unfortunately
No. Perfect equality means that nobody can excel in anything, anywhere and any time. With perfect equality comes stagnation. If you happen to know Rush' song "The Trees" you'll know what I'm talking about:
Now there's no more oak oppression For they passed a noble law And the trees are all kept equal By hatchet, axe, and saw
It is not so much inequality which can be a problem but the fact that the lower bounds can be too low for an acceptable quality of life. As long as the lower bounds are high enough - above the "poverty line" - there can be inequality without that being a problem in and of itself.
Another thing which can be a problem is the reason for there being inequality, e.g. when some rule or custom creates artificial limits for some people but not for others ("discrimination").
For a society to thrive you want people to make the best of their possibilities and to use their capabilities to the fullest extent. With that you automatically get inequality because not everyone has the same possibilities and capabilities, e.g. a farmer on a rock-infested piece of glacial detritus will not be able to produce bumper crops even if he is at least as capable as the farmer in the river delta who can not leave his wooden shoes outside without them sprouting roots and growing leaves. On that same river delta a capable farmer will be able to more reliably produce good crops than one who has never heard of crop rotation. If you take the most productive developer in your company and provide him with a fully equipped tool shop he will not be able to produce as good a widget as would the most experienced mechanic who in his turn would not be as productive a developer. Both can do their best to reach their local optimum but the developer will most likely see that result in higher earnings than the mechanic will.
Inequality is not a problem. Equity - forced equality as personified by the "they" in the lyrics to "The Trees" - is a problem.
* https://www.researchgate.net/profile/Shrehan-Lynch/publicati...
In the 1930s, Claude Shannon was trying to optimize the phone network's automatic switching fabric built out of millions and millions of relays when he, more or less by accident, proved that switching circuits are equivalent to Boolean algebra, in a deep sense, and so the appropriate arrangement of switches, can compute anything that can be computed.
The first major commercial application for the vacuum tube was not in radio, but in amplifying long-distance telephone links. They would quickly find use in frequency multiplexing telephone lines, too. [1]
Similarly, one of the first applications of vacuum tubes as a high-speed electronic switch was for multiplexing telegraph lines, and much of the initial research on high-reliability low-power tubes able to switched fully on without damage began, with the telephone and telegraph companies.
The first computers were built out of relays and vacuum tubes specially designed for telecommunications.
The transistor was invented at Bell Labs. The planned application was the telephone network. The very same year, the theory behind modern error correcting codes was developed at Bell Labs too. These find extensive use today in data storage in computers, but the original goal was arbitrarily accurate transfer of telegraph data over noisy links.
Digital transmission of photographs dates to the late 1920s too; they wanted to send images over extremely noisy long-distance telegraph links. So record the intensity of light over each spot of the image on paper tape. Then send the tape over the wire. And reverse on the other end. [2]
I've come to understand the computer revolution as really the story of the telecommunication revolution. Computers serendipitously came about with advances in telecommunications, enabled by the same technologies, and indeed, often driven by the needs of telecommunications. (One of the very first applications for a computer in an embedded context - dating to the late 1950s in experiment - the telephone exchange, of course.)
[1] https://long-lines.net/tech-equip/misc/Graybar103-0693.jpg
IP routers now do this faster.
The ENIAC was invented to do mathematical calculations for the army.
Blaise Pascal invented a mechanical calculator to do arithmetic in 1642. Leibniz improved on his design and made his own version in 1673. However, not many of either version were made, as it was still cheaper to just do the addition, subtraction, multiplication, and division yourself.
Herman Hollerith invented a punch card tabulating machine and patented it in 1884. It was used to process the 1890 US Census. It could increment counters to do addition and multiplication, but its main purpose was to assist with processing large amounts of data using punch cards, the way SQL databases are used today.
In 1930, Vannevar Bush invented a machine called the Differential Analyzer, which was an analogue computer that could solve differential equations by integration. You could store functions in it by adjusting gears. The purpose was to be able to automatically calculate things like the position of a projectile moving through the air after n seconds without having to calculate it by hand.
Most of this I got from the book ENIAC, The Triumphs and Tragedies of the World's First Computer, which touches on all these predecessors to the computer.
Bush was Claude Shannon's graduate advisor.
I sometimes wonder how much crazy stuff these people didn't write down because they only knew how to make little bits of it happen with current tech.
Then Elon came along… Starlink is probably one of the most useful inventions next to the lightbulb, DC current, Solar Cells, Toilets, desalination/ro and the WWW. I’ve gotten 100mb+ out in places where you have no cell service, no humans, no life, and no way of contacting anyone if in trouble. Starlink kept the connection no problem.
I’m excited for the future if we can just get over our differences. XR, Starlink, EV’s, Highspeed rail, Electric planes, Mars…
Technically, it's a pretty neat trick - architecturally, it works just like any cellular network, except the power is moving, not the subscriber.
The unwillingness is from the government
+ per minute billing from your telco and your ISP.
I simply replied “Air Warrior 3”.
That wasn’t how it worked. You could have a T1 with certain channels configured for voice and others for data, but the configuration was static — you didn’t get to use the bandwidth from the voice channels when they were idle.
> It’s also why ISDN didn’t connect at 128k but at 112k since it just used two “bonded” lines of the T1
ISDN bearer channels were 8-bit clean. If you bonded both channels of a BRI, you had a 128kbps data path. What you typically couldn’t use was the 16kbps D channel, which was used for signaling.
But, the fundamental channel width was 64kbps and ISDN data calls were not routinely connecting at 56kbps due to robbed-bit signaling, which the GP comment claimed.
When 56k modems first came out I was able to get full speed, and it was a great upgrade. Then we moved and I could never pass 28.8 or so.
Turns out in their infinite wisdom in the new development we moved to the phone company divided things up even more so they could get two lines out of what should have been one. 28 + 28 = 56.
I don’t know if they were using some sort of compression or something so that it wasn’t audible on voice calls but it meant a modem was capped forever.
The wait for cable internet was interminable (it came before DSL).
I wonder if that config screwed them when it came time to try to sell DSL. It still wasn’t available years later when I moved out.
56 kbps pushes close to the theoretically available channel bandwidth.
That's all there is to it: information coding theory.
To get more than around 56 kbps from modems, you would need more fidelity from the underlying lines: a wider-band, lower noise pure copper end-to-end connection, or higher bitrate codecs.
The article explains that every 8th bit is lost to allow for control signalling that steals the 8th LSB on every 6th frame. Hence 7/8 * 64 = 56.
I remember trying this a few times while at my parents' store. My dad would tell me which phone line I could use that day - either the dedicated line used to process credit cards (if they were closed), or a spare line off the PBX. But occasionally, I was allowed the use of both - and luckily had a pair of PCMCIA modems with the dongles in different places - and could get speeds well above 56k.
> DSL isn't really fundamentally different from a 56k
There's a great deal of additional integrated digital signal processing to make DSL work that was too costly for consumer modems at the time. I wouldn't agree with this assessment. And other than operating on phone lines for last mile it is completely different on all the layers and uses completely different equipment.
> 56k hit a wall because circuit switching has fundamental disadvantages. Packet switching allowed us to get past that.
There were circuit switched networks far faster than 56k, so not sure this had much to do with any inherent limitation.
Packet switching has obvious advantages for network utilization and was a necessary evolution but I don't think it is relevant to any 56k limit or the revolution in DSP that make multi-megabit over copper pairs possible.
Unless we're limiting to the purely theoretical this is quite the hyperbole and in that case applies equally well to the 56k modem.
Size and heat are also factors. The process nodes did not exist in the 70s and early 80s to produce the integrated circuits necessary. VLSI technically enabled DSL.
The idea that somehow the difference between 1960s integration and 1990s is "purely economic" is pretty silly. If only they threw trillions of dollars more into research in the 60s would we have had the Intel Pentium then rather than 30 years later, maybe, but that is a useless line of reasoning. Someone has to actually do the "science".
You need to actually design and produce a suitable line card equivalent for every subscriber that will support DSL speeds without taking up the space of an airport for it and the cooling. That didn't exist for decades before DSL was rolled out (which started barely a decade after it was patented).
> DSL technology was perfected before the 56K modem was even invented.
Considering that DSL standards continued to evolve after the 56K modem was obsolete this is also hyperbole.
The other thing not yet mentioned which is pretty fundamental is that DSL eschews the 3.3khz bandwidth of POTS.
From <https://www.10stripe.com/10blog/>:
> The blog has been discontinued due to Wordpress security concerns.
Keep this tragedy in mind next time you pick your tech stack.
The thing that allowed speeds to increase to 56kbit/s was digital connections at the ISP end: typically the ISP would get a T1 or E1 circuit fed into a box that would act as 24 modems, but purely digital and synchronized with the telco. So the signal now went Ascend MAX (isp) -> T1 (telco) -> DAC (telco) -> ADC (modem), providing much less quantization noise.
All we get is “Long ago, when the phone networks were still completely analog, when the first real phone networks were being built, the engineers that were designing them faced a decision.” Who were those engineers? What company? How did they test what would be adequate bandwidth?
Legacy of https://en.wikipedia.org/wiki/12-channel_carrier_system
How common was it in the US and elsewhere?
Back in the day, our incumbent telco was quite cutting edge technologically.
7 * 8000 = 56,000 = 56k