295 lines
16 KiB
Plaintext
295 lines
16 KiB
Plaintext
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Secrets of the Little Blue Box
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(Part II)
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A GUIDE FOR THE PERPLEXED
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"But wait a minute," I stop Gilbertson. "if everything you do sounds like
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phone-company equipment, why doesn't the phone company charge you for the call
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the way it charges its own equipment?"
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"Okay. That's where the 2600-cycle tone comes in. I better start from the
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beginning."
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The beginning he describes for me is a vision of the phone system of the
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continent as thousands of webs, of long-line trunks radiating from each of the
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hundreds of toll switching offices to the other toll switching offices. Each
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toll switching office is a hive compacted of thousands of long-distance tandems
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constantly whistling and beeping to tandems in far-off toll switching offices.
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The tandem is the key to the whole system. Each tandem is a line with some
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relays with the capability of signaling any other tandem in any other toll
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switching office on the continent, either directly one-to-one or by programming
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a roundabout route several other tandems if all the direct routes are busy. For
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instance, if you want to call from New York to Los Angeles and traffic is heavy
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on all direct trunks between the two cities, your tandem in New York is
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programmed to try the next best route, which may send you down to a tandem in
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New Orleans, then up to San Francisco, or down to a New Orleans tandem, back to
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an Atlanta tandem, over to an Albuquerque tandem and finally up to Los Angeles.
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When a tandem is not being used, when it's sitting there waiting for someone
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to make a long-distance call, it whistles. One side of the tandem, the side
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"facing" our home phone, whistles at 2600 cycles per second toward all the home
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phones serviced by the exchange, telling them it is at their service, should
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they be interewted in making a long-distance call. The other side of the tandem
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is whistling 2600 c.p.s. into one or more long distance trunk lines, telling
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the rest of the phone system that it is neither sending nor receiving a call
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through the trunk at the moment, that it has no use for that trunk at the
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moment.
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When you dial a long-distance number the first thing that happens is that you
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are hooked into a tandem. A register comes up to the side of the tandem facing
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away from you and presents that side with the number you dialed. This sending
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side of the tandem stops whistling 2600 into its trunk line. When a tandem
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stops the 2600 tone it has been sending through a trunk, the trunk is said to be
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"seized," and is now ready to carry the number you have dialed -- converted into
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multi-frequency beep tones -- to a tandem in the area code and central office
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you want.
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Now when a blue-box operator wants to make a call from New Orleans to New York
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he starts by dialing the 800 number of a company which might happen to have its
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headquarters in Los Angeles. The sending side of this New Orleans tandem stops
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sending 2600 out over the trunk to the central office in Los Angeles, thereby
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seizing the trunk. Your New Orleans tandem begins sending beep tones to a
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tandem it has discovered idly whistling 2600 cycles in Los Angeles. The
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receiving end of that L.A. tandem is seized, stops whistling 2600, listens to
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the beep tones which tell it which L.A. phone to ring, and starts ringing the
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800 number. Meanwhile a mark made in the New Orleans office accounting tape
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indicates that a call from your New Orleans phone to the 800 number in L.A. has
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been initiated and gives the call a code number. Everything is routine so far.
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But then the phone phreak presses his blue box to the mouthpiece and pushes
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the 2600-cycle button, sending 2600 out from the New Orleans tandem notices the
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2600 cycles are coming over the line again and assumes that New Orleans has hung
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up because the trunk is whistling as if idle. The the L.A. 800 number. But |