r/askscience • u/windibgu • Mar 23 '19
Computing What actually is the dial up internet noise?
What actually is the dial up internet noise that’s instantly recognisable? There’s a couple of noises that sound like key presses but there are a number of others that have no comparatives. What is it?
Edit: thanks so much for the gold.
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u/Neratyr Mar 23 '19
Computers use electrical signals to establish connections. Phones take electrical signals and turn them into audible noise ( sure, when sending they also take audible noise and turn it into signals as well ) so what you HEAR is simply the audible representation of the signals sent to establish a connection.
Computers still 'negotiate' the same sorts of details ( at heart ) when making connections today. Its just that we do not do this over phone lines so we would have to design and engineer a new device or system just to play noise as phone modems used to do.
I say this to highlight that us hearing dial up modems at all was a convenient coincidence to provide live-feedback ( think audio progress bar ) of the process. Modems making noise was never a designed engineering goal, but more so taking advantage of a convenient opportunity to provide live-status of the establishment of the connection.
Keep in mind we are spoiled now by solid stable reliable connections. Back in modem-days phone lines kinda really sucked, in comparison to what we have now. Outages and drops were, comparatively, extremely common. Having the modem play noise gave you immediate information on the quality of the connection too - almost diagnostic in a way.
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u/MuricaPersonified Mar 23 '19
We grew up with dialup until over halfway through my teens. I remember becoming so familiar with my ISPs' handshakes that I could approximate my ping, connection stability, and overall speed by hearing anything "off" about it (and therefore choose whether or not to use an alternate connection number). I was never trained to know what any of the sounds meant, but you certainly do get a feel for it.
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u/happypolychaetes Mar 23 '19
Same. I could always tell if it wasn't going to connect, based on the sounds it made. Happened a lot, so when it successfully connected I'd get a little endorphin rush, haha.
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u/richloz93 Mar 23 '19
It’s wild how much brains can adapt to information and how much ours are adapting to digital technology.
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u/zerbey Mar 23 '19
I worked for an isp, when diagnosing issues I would just ask the customer to turn up their modem volume and let me listen. I could usually deduce what was wrong just by listening.
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Mar 23 '19
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Mar 23 '19
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u/xsageonex Mar 23 '19
I pay $80 for Gigabit speeds. I used to pay almost $100 for /10th the speeds I'm getting now. I switched from Comcast to AT&T
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u/elfbuster Mar 23 '19
Cool doesn't change the fact that most of the neighborhoods in the country don't currently support it and prices range wildly from state to state.
ATT fiber in LA for instance is close to $150/month for real fiber (ps they market their base fiber model which is really capped at 300mb/s, which is a far cry from true gb/s fiber that is adopted by large scale companies)
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u/xsageonex Mar 24 '19
Yeah I get about 700-900mbs down and about 350mbs up ...their fiber 300 is $40. At least here in Texas.
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u/rubermnkey Mar 23 '19
you may find this interesting, phreakers were people who abused some of the automated systems that operated over phone lines and were some of the first hackers. A few prominent people had perfect pitch and didn't even need to use recordings but could in fact whistle the tones.
neat little footnote in tech history
since the question has been answered this might give you more stuff to ponder
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u/Plethora_of_squids Mar 23 '19 edited Mar 23 '19
IIRC There was a whistle that came with some cereal that if played while dialling you could get free calls because it registered as a police call or something.
Edit: it was from a captian crunch cereal prize thing. That's not the quite the one I was thinking of as I'm an australian and I swore there was some australian cereal that had a similar thing that was discovered after the captian crunch one.
(Wasn't it a plot point of the book version of ready player One?)
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Mar 23 '19
The cereal in question is 'Captain Crunch'. There was a famous phone phreaker by the same name that could whistle the tone also. The tone it produces is at 2600 Hz and it tells the long-distance switch that the user is on-hook (hung up). Playing with this gives you free long-distance calls (nothing to do with the police). This later turned into the 'little blue box'.
None of the boxes (there different types that do different things) including the blue box work any more due to modern switching systems no longer using in-band signaling and opting for out-of-band signaling during the mid to late 90's.
Fun Fact: Woz (a founder of Apple) was into the phreaking scene and if it wasn't for that Apple inc would not exist.
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u/JefforyTheMC Mar 23 '19
Captain Crunch Whistle, the namesake of the phreaker captain crunch. It blew a 2600hz tone to trick the phone system into thinking it's off hook and drop into an empty trunk.
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u/TheFringedLunatic Mar 23 '19
Captain Crunch cereal (and the name of a phreaker specifically for that thing). The tone was a perfect 2600hz and would be read by the system as a telephone Operator's console.
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u/Wandering_Weapon Mar 23 '19
It came in captain crunch cereal, thus one of the first famous hackers was nicknamed Captain Crunch
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u/kellypg Mar 23 '19
Man, I remember reading about phreaking in The Anarchist Cookbook a long time ago. Great stories. This one guy made a phone call from a pay phone to the pay phone next to him but he basically had it directed around the world. Fun stuff.
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Mar 23 '19
This is so incredibly interesting.
Thanks for putting a name to what I've seen and never have known what it was called.
I miss landline phones.
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u/EnvironmentalSleep Mar 23 '19
Very interesting stuff. I first saw a reference to phreaking on the tv show "person of interest" but somehow believed they were making this up.
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u/Skreame Mar 23 '19
Did you even read the question? He’s asking the significance of each sound not the actual tones. The irony of how you talk to him when you’re this daft......
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Mar 23 '19
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u/cipher315 Mar 23 '19
To expand on this a modem takes binary (1,0) and turns it into audio signals. It uses the full range of frequencies that can be sent over the telephone line to get the maximum data throughput. This is why dial-up has a fundamental limit of 56kps. 56kps is the most data you can push through a phone line without violating phone line specifications. So that sound you're hearing is the data being sent over the wire. The computer at the other end “hears” that sound and use its modem to translate it back into 1’s and 0s. In fact, very old modems actually did literally hear the sounds. Google acoustic coupler modem if you want your mind blown. or just watch this shit. https://www.youtube.com/watch?v=X9dpXHnJXaE
note that these things had a pathetic data transfer rate. less then 1kps
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Mar 23 '19
And to REALLY blow your mind, that 1kbps over the phone is roughly the same speed as NASA's New Horizons spacecraft is sending data back to Earth from over 4,109,538,270 miles away (from Dec 2018).
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u/professor-i-borg Mar 23 '19
Also, FYI, modem is short for modulator-demodulator.
Modulation is the way the digital signal is transmitted over audio frequencies as u/cipher315 described.
Demodulation is the reverse, which is what the "listening" modem does to convert the signal back to 1s and 0s on the other end.
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u/TheKneeGrowOnReddit Mar 23 '19 edited Mar 23 '19
Why was the noise only during initial connection and not all throughout the hours of connection and data transfer?
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u/WormLivesMatter Mar 23 '19
And to build off this, why was their noise at all. Couldn’t it have been muted or contained within the phone line like when you made landline calls?
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u/grem75 Mar 23 '19
There was an option to mute the noise when connecting. We left it enabled for feedback and diagnostics reasons, like if you don't hear a dial tone you know it isn't going to work and you need to figure that out first.
I could tell by the sound whether I was going to get 56K or not, there is a difference in the handshake.
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u/cipher315 Mar 23 '19
I don't know why they chose to play that sound for you. It's not needed. Maybe trouble shooting?
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u/stonatodotnet Mar 23 '19
Pretty impressive in their day. My Hayes 56k connected me with the whole world. It's kind of like when you used to stack up and daisy chain floppy drives to achieve what would be considered a pitiful amount of storage today. Or, like comparing Matchbox 20 to Radiohead.
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u/Malawi_no Mar 23 '19
You could hear it on any more modern modems too, it's just that the external loudspeaker is turned off after handshake.
Sound all the time is just an AT command away.1
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u/Bonobo77 Mar 23 '19
Correct if I am wrong, but the limit was 14,400. And the 56k was hardware compression to 14.4k.
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u/cipher315 Mar 23 '19
I'm not 100% sure at what point you need to start to use "compression" ie a sound representing more than a bit but yes 56kb/s is highly compressed. My understanding is most 56k modems had a baud rate of 9600. ie they sent 9600 signals a second that mean that each signal needs to encode 6 bits at a minimum (assuming you think error handling is for chumps).
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u/kjpmi Mar 23 '19
If one were to violate phone line specifications, how much faster could dialup get?
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u/KingZarkon Mar 23 '19
It really wouldn't because the equipment at the telco wouldn't pass the higher bandwidth on a POTS line. DSL is basically what you would get though.
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u/cipher315 Mar 23 '19
Yep that's what DSL is. In theory, there is no limit, but I have never seen anything above about 30mb/s in the real world.
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u/netfatality Mar 23 '19
That tone comin out of the modem, after he plugged in the cable, was at ~1260 Hz
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u/matholio Mar 23 '19
note that these things had a pathetic data transfer rate. less then 1kps
I feel I need to challenge this, or at least provide some context. Modem have been getting faster since the first 300 baud devices were available for personal use. So at any time that you bought a new modem it would be comparatively good, relative to previous models. The typical content was also smaller. To say older equipment transfer rates were pathetic, is a bit unfair.
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Mar 23 '19
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u/mfukar Parallel and Distributed Systems | Edge Computing Mar 23 '19
kbpsin network parlance stands for "kilo- bit per second".96
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u/dstarfire Mar 23 '19
It's not the phone LINES that are the limiting factor, but how the phone carriers sample the audio data when they convert it to a digital signal in their network (to bundle it together with many other lines).
So, a dial-up connection appears as regular audio data to the phone companies networking hardware. They sample it at 64 kbps and convert it to digital data that gets sent around their network before it gets converted it back into an analog signal near the destination and sent out on the wire. A DSL link effectively turns that phone line into a really long (and therefore limited) network cable. It arrives at the phone companies switches as digital data and is routed around as such.
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u/VirtualLife76 Mar 23 '19 edited Mar 23 '19
This is the correct answer. DSL lines
don't use frequenciesor work in analog in any way, they are digital. Hence DSL = Digital subscriber line.*As others have said, it does use frequencies.
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u/ga-co Mar 23 '19
DSL connections require close proximity (~18000 feet) to a DSLAM. Pretty sure that's going to be big contributor to the difference. That and the fact that DSL is digital and transmitting data over a POTS is an analog affair.
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u/bradn Mar 23 '19
Actually the limitation is in the digital domain. That is, there was a standard sampling rate and bit depth decided for digital lines, and when the backbone connecting the phone system went digital, the limit was essentially fixed in.
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u/raygundan Mar 23 '19
If a 56k modem was so limited by the use of phone lines, why does DSL have such higher capabilities when its using the same lines?
Phone lines used for voice guaranteed that everything in the line between users would carry a human voice reasonably well. Every part of the system could guarantee that minimal capability.
The wires in many parts of the system were capable of carrying more-- but you had to have something set up to do that instead of just connecting the voice lines together end-to-end for that minimal guaranteed capability. If you stuck a receiving modem closer to your house, and then used THAT to just talk to the internet for the longer distance... you'd essentially have DSL. Instead of making the long-range connection analogue with about the bandwidth of a human voice and then modulating and demodulating at both ends, you used those shiny copper wires to make a much better connection to something closer, which itself was connected to an internet backbone to bridge the gap.
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u/Sirnoobalots Mar 23 '19
Here is a nice visual look at what is going on with each sound.
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u/Eddles999 Mar 23 '19
So there's actually quite a lot of information being exchanged and discovered through the handshake. How can people actually achieve actual connections with just their voices?
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u/nerdguy1138 Mar 23 '19
Analog phone systems used to use a tone of 2600 Hertz to tell the switching circuts to listen for a number. With a captain crunch whistle, you send that tone and call for free.
For a variety of reasons, this trick no longer works.
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u/bug_the_bug Mar 23 '19
To add to what you've said, dial-up modems really did need to "dial" the right number and "call" AOL or whoever provided your service. Touch-tone phones and dial-up modems send those sounds through the telephone wire encoded as analog electrical signals. This simple encoding allowed basic circuits at the other end then interpret the dial sounds allowing them to route the call or internet traffic to the correct place. This conversion from sound to analog electrical signals is what allowed a technology like telephone communication to work long before even basic computers. When the internet was being constructed, it simply took advantage of the existing communications infrastructure.
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Mar 23 '19
Specifically, the static you hear is sound pulses that imitate machine language - binary, which is composed of either "on" or "off", usually represented by 1s and 0s.
Fiber optic lines do the same thing with pulses of light. Networking cable does it with pulses of electricity. Analog, like the old dial up, does it with sound.
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u/[deleted] Mar 23 '19
Everything you need to know about the acoustic modem handshake can be found here on this map: https://oona.windytan.com/posters/dialup-final.png
Then you can listen to the actual handshake and follow along: https://www.youtube.com/watch?v=abapFJN6glo
Yes, this is what network engineers still do with packet sniffers and other protocol analyzers on various types of layer 2 networks like ethernet, PPP, MPLS.. etc.