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Modem Love
January 31, 2013 12:04 PM   Subscribe

Remember the sound of dialup modems handshaking? Here's what was happening.
posted by pjern (28 comments total) 41 users marked this as a favorite

 
Turns out that twangy ba dong BA DONG is "a wide-spectrum probing signal in both directions to do measurements of the telephone line." Fascinating.
posted by theodolite at 12:14 PM on January 31, 2013


That is an awesome picture. I finally understand, and now I can go ahead and completely forget all of it.
posted by blue_beetle at 12:15 PM on January 31, 2013


Who could forget? Wonder if it's available as a ringtone.
posted by de at 12:16 PM on January 31, 2013 [6 favorites]


The way the transactions are transcribed is oddly reminiscent of Drone/Mind conversations in Iain M. Banks' books. Nice!
posted by Jon Mitchell at 12:24 PM on January 31, 2013 [1 favorite]


When I looked at the picture I panicked momentarily when I saw v.42 LAPM but not v.42 bis. I began to doubt myself, had I been walking around all these years with a flawed understanding of Lempel-Ziv data compression, error correction and CCITT standards? Turns out I was not wrong, v.42 bis is the CCITT standard for 38k modems. I can remain secure in my knowledge of obsolete standards one more day.
posted by Ad hominem at 12:27 PM on January 31, 2013 [3 favorites]


I wonder how long it would have taken to view that image if I was on dial-up compared to now.

However,, listening to the sound still makes my heart race a bit faster.
posted by MCMikeNamara at 12:28 PM on January 31, 2013 [2 favorites]


I wish I could share my excitement over that infographic with friends and family.
But alas.
posted by tybeet at 12:35 PM on January 31, 2013 [1 favorite]


What I never really understood was why we had to hear the modem screeching and squawking. They had speakers! And volume knobs! WTF!

Was that feature just so you could do the (even more) old school phone cradle thing?
posted by Sys Rq at 12:36 PM on January 31, 2013


I still remember getting my second phone line installed so I could run a BBS over a 2400 baud modem. It turned out that the line serving our neighbourhood was only able to handle a single line per house so to get a second line they had to run another line in from the access box on the end of the block. The $60 cdn installation fee resulted in a 3 days of work for 5 guys a digger and the destruction of the back two meters of all of my neighbours on one sides' yards.

That graphic is off the hook.

What I never really understood was why we had to hear the modem screeching and squawking. They had speakers! And volume knobs! WTF!

Was that feature just so you could do the (even more) old school phone cradle thing?


It was because everyone used to use shared lines. You needed to know if a human or fax machine answered the line.
posted by srboisvert at 12:43 PM on January 31, 2013


I think the phone cradle thing was only to get around Bell restrictions on plugging shit into their network.

Oddly, you could set your modem to leave the speaker on thought the whole session with the ATM command so you could listen to the entire call, not just the handshake. You could use it hear when someone picked up another extension to make a call and fucked up your download.
posted by Ad hominem at 12:47 PM on January 31, 2013


By phone cradle thing, I mean acoustic couplers. I'm pretty sure you can still buy them if you want to dial in to something from a pay phone.
posted by Ad hominem at 12:48 PM on January 31, 2013


The number is signaled to the network using Dual-Tone Multi-Frequency signaling, or DTMF...

No wonder my connections always dropped. My motherfucking modem was getting dumped.
posted by slogger at 1:11 PM on January 31, 2013 [4 favorites]


And this is also why credit card machines still use 300 baud modems - they have a quicker handshake and since there's a tiny number of bits to transmit for a single transaction, the handshake time dominates the total transaction time.
posted by GuyZero at 1:27 PM on January 31, 2013


There is some serious negotiation going on just to play a couple rounds of TW2002
posted by MiltonRandKalman at 1:40 PM on January 31, 2013 [2 favorites]


Forgetting my ATL0M0 was a sure way to get a stern talking to from my erstwhile napping dad.
posted by kmz at 1:46 PM on January 31, 2013 [1 favorite]


previously
posted by helion at 2:06 PM on January 31, 2013


I'm interested in the "disabling echo suppressors and cancelers" part. I was under the impression that phone systems ignored line audio commands after blueboxing, did they leave in some specific signal handling as modems became more popular?

What other commands can still be sent to PSTN over customer audio?
posted by odinsdream at 2:14 PM on January 31, 2013


Speed it up and you get Autechre. Slow it down and you get Merzbow.
posted by davebush at 3:14 PM on January 31, 2013


From the wikipedia page on echo cancellation: " Some telephone devices disable echo suppression or echo cancellation when they detect the 2100 or 2225 Hz "answer" tones associated with such calls, in accordance with ITU-T recommendation G.164 or G.165."

The tone so marked in the diagram looks like it's around ~2200Hz.
posted by smidgen at 3:39 PM on January 31, 2013


No wonder my connections always dropped. My motherfucking modem was getting dumped.

Darn you Slogger, you beat me to the DTMF(A) joke!
posted by Grandysaur at 5:18 PM on January 31, 2013


Wonder if it's available as a ringtone.

iPhone and Android.
posted by ChurchHatesTucker at 6:20 PM on January 31, 2013 [3 favorites]


de writes "Who could forget? Wonder if it's available as a ringtone."

Yep. And it's a great way to separate the older nerds from the the riff raff when your phone rings.

Sys Rq writes "What I never really understood was why we had to hear the modem screeching and squawking. They had speakers! And volume knobs! WTF!"

A learned ear could tell when something was going wrong and sometimes what the nature of the problem was. When I used to dial up into my college I could tell when the high *cough 14.4* speed modem bank was all busy and I was getting connected at 2400. In which case I'd just hang up and try later. Also the silence at the beginning allowed you to assess the quality of the connection. A static filled dial tone was sure to be problematic.
posted by Mitheral at 6:29 PM on January 31, 2013 [2 favorites]


Now is a good time to bring up that when Kevin Mitnick was arrested, they put him in solitary confinement for 8 months because they were worried that he would whistle PPP packets into the phone, as if he was some sort of cross between Neo and John Draper (and this was pre-Matrix).
posted by about_time at 5:14 AM on February 1, 2013


I remember seeing an animation that showed the Truth behind this. It was all being done by a pair of old ladies sitting somewhere at a swtichboard. I looked but could not find it.
posted by Goofyy at 6:05 AM on February 1, 2013


Here it is.
posted by stebulus at 6:47 AM on February 1, 2013 [2 favorites]


Thank you, stebulus. That's the one. I'd forgotten it was British.
posted by Goofyy at 6:52 AM on February 1, 2013


Related previously.
posted by Chrysostom at 8:32 AM on February 1, 2013


@Jon Mitchell - what's odder still is that's exactly what this reminded me of too (was coming to comment), but then I am reading Excession at the mo.
posted by 6am at 5:01 PM on February 3, 2013


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