Oona Räisänen has written a thorough and engrossing article about the noises emitted by dial-up modems while they connect and handshake, and the accompanying graphic (ZOMG HUGE) is nothing short of spectacular. It would make a great full-size poster -- maybe a framed art-print.
Now the modems must address the problem of echo suppression. When humans talk, only one of them is usually talking while the other one listens. The telephone network exploits this fact and temporarily silences the return channel to suppress any confusing echoes of the talker's own voice.
Modems don't like this at all, as they can very well talk at the same time (it's called full-duplex). The answering modem now puts on a special answer tone that will disable any echo suppression circuits on the line. The tone also has periodic "snaps" (180° phase transitions) that aim to disable yet another type of circuit called echo canceller.
Now the modems will list their supported modulation modes and try to find one that both know. They also probe the line with test tones to see how it responds to tones of different frequencies, and how much it attenuates the signal. They exchange their test results and decide a speed that is suitable for the line.
After this, the modems will go to scrambled data. They put their data through a special scrambling formula before transmission to make its power distribution more even and to make sure there are no patterns that are suboptimal for transfer. They listen to each other sending a series of binary 1's and adjust their equalizers to optimally shape the incoming signal.
The sound of the dialup, pictured
Ethan Zuckerman — formerly of Global Voices, now at the MIT Center for Civic Media — has spent his career trying to find thoughtful, effective ways to use technology as a lever to make positive social change (previously), but that means that he also spends a lot of time in the company of people making […]
If you’re a student journalist and want to attend HOPE XI, the Eleventh Hackers on Planet Earth conference (July 22-24, NYC) you can win free admission (and an interview with me!) by submitting an article about any of the topics come up at HOPE conferences! Get writing!
Earlier this month, I gave the afternoon keynote at the Internet Archive’s Decentralized Web Summit, and my talk was about how the people who founded the web with the idea of having an open, decentralized system ended up building a system that is increasingly monopolized by a few companies — and how we can prevent the same things from happening next time.
Experienced shutterbugs with DSLR cameras have boatloads of lens options for capturing the moment. Unfortunately, smartphone photographers often get stuck with their one crummy lens, which means limited zoom and focus for their final image.Step up your smartphone’s photographic power with the Acesori 5-Piece Smartphone Camera Lens Kit, now just $9.99 in the Boing Boing Store.Magnetic rings easily […]
Some truths are universal. For one, your phone will always run out of power when you most need it. For another, the charging cords that come packaged with your Apple device will fray, split, and rip faster than Usain Bolt in a game of tag.Instead, pick up a charging cord that anyone would have a tough […]
Some people say magic tricks are nerdy and best left to your 12-year-old asthmatic cousin. But others see value in perfecting the slight of hand and showmanship associated with a perfectly executed routine. We’re firmly in the latter camp. And now, we’re giving you the ability to put a few parlor tricks up your sleeve with the Penguin […]