Blue box
A blue box device allowed for circumventing these charges by enabling an illicit user, referred to as a "phreaker," to place long-distance calls, without using the network's user facilities, that would be billed to another number or dismissed entirely by the telecom company's billing system as an incomplete call.
Soon after, models of relatively low quality were being offered fully assembled, but these often required tinkering by the user to remain operational.
This new system allowed the telephone network to be increasingly automated by deploying the dialers and tone generators on an as-required basis, starting with the busier exchanges.
In the film, the tone sequence for sending a complete telephone number is heard through a loudspeaker as a technician presses the keys for dialing.
Before the technical details were published, many users discovered unintentionally, and to their annoyance, that a 2600 Hz tone played into the caller's handset would cause a long-distance call to disconnect.
He became fascinated with the phone network, and over the next decade had built up a considerable base of knowledge about the system and how to place calls using the control tones.
[citation needed] He and other phone phreaks, such as "Bill from New York" and "The Glitch", trained themselves to whistle 2600 Hz to reset a trunk line.
Twelve DPDT pushbuttons, labelled KP, ST and the 10 digits, would operate pairs of plungers to play the phone company tones, after the E7 piano key had been pressed and released.
It was possible to construct an electronic blue box with 1940s vacuum tube technology, but the device would have been relatively large and power hungry.
A common hack was to use a TI-30 pocket calculator as the chassis of the device, with the diodes for the switch matrix wired into the keypad.
So, some hackers went to the extra trouble of building blue boxes that stored telephone numbers and played the tones with the same timing as the machines.
The widespread ability to blue box, once limited to just a few isolated individuals exploring the telephone network, developed into a subculture.
[12] Suddenly, many more people wanted to get into the phone phreaking culture spawned by the blue box, and it furthered the fame of Captain Crunch.
[17] All sold issues were recalled or seized from newsstands by police and officials of Pacific Bell, causing financial loss to the magazine.
[19] The June 1975 issue of 73 magazine carried an article describing the rudiments of the long-distance signaling network, and how to construct and operate red and blue boxes.
When enough digits had been decoded, typically seven in North America, connections between the rotors would select a single line, the customer being dialed.
Over longer distances, the capacitance of the lines filter out any rapid changes in voltage and dialing pulses do not reach the remote office in clean form, so that long-distance calls still required operator intervention.
The tandem would then buffer the remaining digits and decode the number to see which remote exchange was being dialed, generally using the area code for this purpose.
The tandems solved this by buffering the phone number and then converting each digit into a series of two tones, the multi-frequency signaling system, or "MF".
[12] When the call was finished and one of the parties hung up the phone, their exchange would notice the change in voltage and begin playing the 2600 Hz tone into the trunk line.
Once the called end sent the supervision flash, the caller used the blue box to send a "Key Pulse" or "KP", the tone that starts a routing digit sequence, followed by either a telephone number or one of the numerous special codes that were used internally by the telephone company, then finished with a "Start" tone, "ST".
Armed with records of all long-distance calls made, kept by both mechanical switching systems and newer electronic switching systems, including calls to toll-free telephone numbers which did not appear on customer bills, telephone security employees began examining those records looking for suspicious patterns of activity.
In the early days, the lists were probably intended to detect equipment malfunctions, but the follow-up investigation did lead to blue box users.
In one 1975 case, the Pacific Telephone Company targeted one defendant's line with the following equipment: These actions resulted in several highly publicized trials.
As this process might take on the order of 10 to 15 seconds, the total wasted time across all of the trunk lines could be used to carry additional calls.
Blue boxing worked if one connected to such an exchange, but could only be used end-to-end if the entire network between the two endpoints consisted only of tandems, which became increasingly rare and disappeared by the late 1980s.
Alternatively, the tones could be recorded on magnetic tape, which would be cut into pieces and spliced together, using a commercial splicer for accurate alignment.
If the phreaker matched machine dialing and recorded at 7.5 ips (inches per second), the splices for tone and silence would be about 1/2-inch long., with KP 3/4-inch long.
Because the connection between the telephone and the telephone network is two-wire, but the signaling on the international circuit operates on a four-wire basis (totally separate send and receive paths), signal-acknowledgment tones (single pulses of one of the two frequencies from the far end of the circuit after receipt of each digit) tended to be reflected at the four-wire/two-wire conversion point.
This guard tone drowned out the echoed acknowledgment signals so that only the blue box-transmitted digits were heard by the digit-receiving circuits at the far end.
