305 lines
19 KiB
Plaintext
305 lines
19 KiB
Plaintext
BIOC.V
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BIOC AGENT 003'S COURSE IN [BASIC TELECOMMUNICATIONS] Part V
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Revised 08-Aug-84 Word Processed by Tharrys Ridenow
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[PREFACE]:
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Previous installments of this series were focused on telephony from a net-
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work point of view. Part V will deal with telephone electronics focusing pri-
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marily on the subscriber's telephone (hereinafter simply referred to as
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"fone.")
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WIRING:
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Assuming a standard one-line fone, there are usually 4 wires that lead out
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of the fone set. These are standardly colored red, green, yellow, and black.
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The red and green wires are the two that are actually hooked up to your CO.
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The yellow wire is sometimes used to ring different fones on a party line (ie,
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one #, several families--found primarily in rural areas where they pay less for
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the service and they don't use the fone as much); otherwise, the yellow is usu-
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ally just ignored. On some two-line fones, the red and green wires are used
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--More--(5%)
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for the first fone # and the yellow and black are used for the second line. In
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this case there must be an internal or external device that switches between
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the two lines and provides a hold function (such as Radio Shack's outrageously
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priced 2 line and hold module- a better one would be the 2-line Silver Box fone
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[yes, it has keys A, B, C, and D, along with 2-line capability for only about
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$60] found in a DAK catalog).
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In telephony, the green and red wires are often referred to as Tip (T) and
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Ring (R), respectively. This naming goes back to the old operator cord boards
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where one of the wires was the tip of the plug and the other was the ring (of
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the barrel).
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A rotary fone (aka dial or pulse) will work fine regardless of whether the
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red (or green) wire is connected to the Tip (+) or Ring (-). A Touch-Tone (TM)
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fone is a different story, though. It will not work unless the Tip (+) is the
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green wire. [Although, some of the more expensive DTMF fones do have a bridge
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rectifier which compensates for polarity reversal.] This is why under certain
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(non-digital) equipment you can reverse the red and green wires on a touch-tone
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fone and receive free DTMF service. Even though it won't break dial tone, rev-
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ersing the wires on a rotary line on a digital switch will cause the tones to
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be generated.
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VOLTAGES, ETC.:
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When your telepone is on-hook (ie, hung up) there is approximately 48
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--More--(13%)
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volts of DC potential across the tip and ring. When the handset of a fone is
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lifted a few switches close which causes a loop to be connected (known as the
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"local loop") between your fone and the CO. Once this happens DC current is
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able to flow through the fone with less resistance, causing a relay to energize
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which then causes other CO equipment to realise that you want service. Eventu-
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ally, you should end up with a dial tone. This also causes the 48VDC to drop
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down into the vicinity of 12V. The resistance of the loop also drops below the
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2500 ohm level, though FCC licensed telephone equipment must have an off-hook
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impedance of 600 ohms.
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As of now, you are probably saying "This is all nice and technical, but
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what the hell good is the information?" Well, also consider that this voltage
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(& resistance) drop is how the CO detects that a fone was taken off hook
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(picked up). In this way, they know when to start billing the called number.
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Now what do you suppose would happen if a device such as a resistor or a zener
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diode was placed on the CALLED party's line so that the voltage would drop just
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enough to allow talking but not enough to start billing? First off, the cal-
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ling party would not be billed for the call but conversation could be persued.
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Secondly, the CO equipment would think that the fone just kept on ringing. The
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Telco calls this a "no-no" (toll fraud to be specific) while phone phreaks af-
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fectionately call this mute a black box.
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The following are instructions on how to build a simple black box. Of
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course, anything that prevents the voltage from dropping would work.
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--More--(22%)
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You only need two parts: An SPST toggle switch and a 10,000 ohm (10 K) 1/2
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watt resistor. Any electronics store should stock these parts.
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Now, cut 2 pieces of wire (about 6 inches long) and attach one end of each
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wire to one of the terminals on the switch. Now turn your K500 (standard desk
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fone) upside down and take off the cover. Locate wire (disconnect from its
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terminal). Now bring the switch out the rear of the fone and replace the cov-
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er.
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Put the switch in a position where you receive a dial tone. Mark this po-
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sition NORMAL and the other side FREE.
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When your phriends call (at a prearranged time), quickly lift and drop the
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receiver as fast as possible. This will stop the ringing (do it again if it
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doesn't) without starting the billing. It is important that you do it quickly
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(less than one second). Then put the switch in the FREE position, pick up the
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fone, and you have a phree incoming call. Keep all calls short and preferably
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under 15 minutes.
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NOTE: If someone picks up an extension in the called party's house and that
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fone is not set for FREE then billing will start.
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NOTE: An old way of signalling a phriend that you are about to call is mak-
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ing a collect call to a non-existant person in the house. Since your
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friend will not accept the charges, he will know that you are about to
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call and thus prepare the black box (or vice versa).
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WARNING: The Telco can detect black boxes if they suspect one on your line.
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--More--(30%)
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This is done due to the presence of AC voice signal at the wrong DC
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level!
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Pictoral diagram (standard rotary K500 fone):
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--------------------------------------------------------------
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******BLUE WIRE****>>>>F<<< |
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| * * |
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****WHITE WIRE**** * |
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| * |
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| RESISTOR |
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| * |
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| * |
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| >>>RR<<<**************SWITCH******** |
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| * |
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**********************************GREEN*WIRE*************** |
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--------------------------------------------------------------
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NOTE: The black box will not work under ESS or similar digital switches
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since ESS does not connect the voice circuits until the fone is picked
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up (and billing starts). Instead, ESS uses an "artificial" computer
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--More--(37%)
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generated ring.
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RINGING:
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To inform a subscriber of an incoming call, the Telco sends 90 volts (RMS)
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of pulsing AC down the line (at around 15 to 60 Hz; usually 20 Hz). In most
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fones this causes a metal armature to be attracted alternately between two
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electromagnets thus striking 2 bells. Of course, the standard bell (patented
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in 1878 by Tom A. Watson) can be replaced by a more modern electronic bell or
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signaling device.
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Also, you can have lights and other similar devices in lieu of (or in con-
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junction with) the bell. A simple neon light (with its corresponding resistor)
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can simply be connected between the red and green wires (usually L1 and L2 on
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the network box) so that it lights up on incoming calls.
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WARNING: 90 VDC can give quite a shock. Exercise extreme caution if you
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wish to further pursue these topics.
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Also included in the ringing circuit is a capacitor to prevent the DC
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current from interfering with the bell [a capacitor will pass AC current while
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it will prevent DC current from flowing (by storing it)]. Another reason that
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the telco hates black boxes is because ringing uses a lot of common-control
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equipment, in the CO, which use a lot of electricity. Thus the ringing genera-
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tors are being tied up while a free call is being made. Usually calls that are
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allowed to ring for a long period of time may be construed as suspicious. Some
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--More--(45%)
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offices may be set up to drop a trouble card for long periods of ringing, then
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a "no-no" detection device may be placed on the line.
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Incidentally, the term "ring trip" refers to the CO process involved to
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stop the AC ringing signal when the calling fone goes off hook.
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NOTE: It is suggested that you actually dissect fones to help you better
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understand them. It will also help you to better understand the
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concepts if you actually prove them to yourself. For example, actual-
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ly take the voltage readings on your fone line (any simple multi-test-
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er [a must] will do). Phreaking is an interactive process, not a pas- sive one!
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DIALING:
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On a standard fone, there are two common types of dialing: pulse and DTMF.
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Of course, some people insist on being different and don't use DT thus leaving
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them with MF (Multi Frequency, aka operator, aka Blue Box!) tones. This is
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another "no-no" and the Telco security gentlemen have a special knack for deal-
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ing with such "phreaks" on the Network.
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When you dial rotary, you are actually rapidly breaking and reconnecting
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(breaking and making) the local loop once for each digit dialed. Since the
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physical connection must be broken, you cannot dial if another extension is
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off-hook. Neither of the fones will be able to dial pulse unless the other
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hangs up.
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--More--(52%)
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Another term often referred to in telephone electronics is the break ratio.
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In the US, the standard is 10 pulses per second. When the circuit is opened it
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is called the break interval, when it is closed it is called the make interval.
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In th US, there is a 60 millisecond (ms) make period and a 40 ms break period.
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(60+40=100 ms = 1/10 s). This is referred to as a 60% make interval. Some of
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the more sophisticated electronic fones can switch between a 60% and a 67% make
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interval. This is due to the fact that many foreign nation use a 67% break in-
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terval. <Editor's note: I have a rather interesting GE fone that switches
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between a strange form of DTMF and pulse dialing. It seems that Telco equip-
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ment will take 20 pulses per second as well for pulse dialing, and you don't
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have to pay extra (I had been experimenting with a line that didn't subscribe
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to touchtone). This fone (from GE: 2-9260A) is ideal for the phone phreak as
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it has 12 number memory and redial of last number in addition to the ability to
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work on a non-DTMF line.>
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Have you ever been in an office or a similar facility and saw a fone wait-
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ing to be used for a phree call but some asshole put a lock on it to prevent
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outgoing calls?
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Well, don't fret phellow phreaks, you can simulate pulse dialing by rapidly
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depressing the switchhook. (If you depress it for longer than a second it will
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be construed as a disconnect.) By rapidly switchhooking you are causing the
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local loop to be broken and made again similar to rotary dialing! Thus, if you
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can manage to switchhook rapidly 10 times you can reach an operator to place
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--More--(61%)
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any call you want! This takes a lot of practice, though. You might want to
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practice on your own fone dialing a friend's # or something else. Incidental-
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ly, this method will work with DTMF fones since all DTMF lines can also handle
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rotary.
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Another problem with pulse dialing is that it produces high-voltage spikes
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that make loud clicks in the earpiece and cause the bell to "tinkle". If you
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never noticed this then your fone has a special "anti-tinkle" and earpiece
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shorting circuit (most do). If you have ever disconnected a rotary fone (a
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must for any serious phreak) you would notice that there are 2 sets of contacts
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that open and close during pulsing (on the back of the rotary dial under the
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plastic cover). One of these actually opens and closes the loop while the oth-
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er mutes the earpiece by shorting it out. The second contacts also activate a
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special anti-tinkle circuit that puts a 340 ohm resistor across the ringing
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circuit which prevents the high voltage spikes from interfering with the bell.
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Dual Tone Multi Frequency (DTMF) is a modern day improvement on pulse dialing
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in several ways. First of all, it is more convenient for the user since it is
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faster and can be used for signalling after the call is completed (i.e. SCC's,
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computers, etc.). Also, it is more up to par with modern day switching equip-
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ment (such as ESS) since pulse dialing was designed to actually move relays by
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the number of digits dialed (in SXS offices). Each key on a DTMF keypad pro-
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duces 2 frequencies simultaneously (one from the high group and another from
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--More--(70%)
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the low group).
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---------------------------------
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| Q | ABC | DEF | |
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697 Hz-| 1 | 2 | 3 | A |
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---------------------------------
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| GHI | JKL | MNO | |
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770 Hz-| 4 | 5 | 6 | B |
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---------------------------------
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| PRS | TUV | WXY | |
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852 Hz-| 7 | 8 | 9 | C |
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---------------------------------
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| |Z OPER| | |
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952 Hz-| * | 0 | # | D |
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---------------------------------
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1209 Hz 1336 Hz 1477 Hz 1633 Hz
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A portable DTMF keypad is known as a white box. The fourth column (1633 Hz) is
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not normally found on regular phones but it does have several special uses. (A
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fone modified to use these 1633 Hz tones is called a silver box, and a portable
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full DTMF keypad is called a gray box.) For one, it is used to designate the
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priority of calls on AUTOVON, the military phone network. The keys are called
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--More--(75%)
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Flash, Immediate, Priority, and Routine (with variations) instead of ABCD.
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Secondly, these keys are used for testing purposes by the telco. In some areas
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you can find loops as well as other neat tests (see part II) on the 555-1212
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directory assistance exchange. For this, you would call up a DA in certain
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areas [that have an Automatic Call Distributor (ACD)] and hold down the D key
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which should blow the operator off. You will then hear a pulsing dial tone
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which indicates that you are in the ACD internal testing mode. You can get on
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one side of a loop by dialling a 6. You can get on the other side by dialling
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a 7. Some phreaks claim that if the person on side 6 hangs up, occasionally
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the equipment will screw up and start routing directory assistance calls to the
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other side of the loop. Another alleged test is called REMOB which allows you
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to tap into lines by entering a special code followed by the 7 digit number you
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want to monitor. Then there is the possibility of mass conferencing. ACD's
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are becoming rare, though. You will probably have to make several NPA-555-1212
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calls before you find one. You can modify regular fones quite readily so that
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they have a switch to change between the 3rd and 4th columns. The plans can be
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found in TAP as well as on many BBS's.
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TRANSMITTER/RECIEVER:
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When you talk into the transmitter, the sound waves from your voice cause
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a diaphragm to vibrate and press against the carbon granules (or another simi-
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lar substance). This causes the carbon granules to compress and contract, thus
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--More--(84%)
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changing the resistance of the DC current flowing through it. Therefore, your
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AC voice signal is superimposed over the DC current of the local loop. The re-
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ciever works in a similar fashion where the simple types utilise a magnet, ar-
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mature, and diaphragm.
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HYBRID/INDUCTION COIL:
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As you may have noticed, there are two wires for the reciever and two for
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the transmitter in the phone, yet the local loop consists of 2 wires instead of
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4. This 4 wire to 2 wire conversion is done inside the phone by a device known
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as an induction coil which uses coupling transformers. The reason 2 wires are
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used on the local loops are because it is a lot cheaper for the Telco. All of
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the interoffice trunks utilise 4 wires. This is necessary for full duplex
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(i.e. simultaneous conversation on both sides) and for amplification devices.
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There are similar devices in the CO's, known as a hybrid, that couple the 4
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wire trunks to the 2 wire local loops and vice versa.
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MISCELLANEOUS:
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In the telephone, there is also a balancing network consisting of a few
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capacitors and resistors which provide sidetone. Sidetone allows the caller to
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hear his own volume in the reciever. He can then adjust his own voice accord-
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ingly. This prevents people from shouting or speaking too softly without not-
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icing it.
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--More--(91%)
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Hold: When a telephone goes off hook, the resistance drops below 2500 ohms. At
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this point, the Telco will send a dial tone. To put someone on hold you must
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put a 1000 ohm resistor (1 watt) across the tip and ring before it reaches the
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switchhook. In this way, when the phone is hung up (for hold) the resistance
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remains below 2500 ohms which causes the CO to believe you are still off-hook.
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You can build a simple hold device using the following pictorial diagram:
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/
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(RED) O--------------------------/
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1000 Ohm | |
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Resistor Ringing |
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| Circuit |
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| | Switch
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/ | hook
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/ SPST switch | |
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/ | |
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--More--(97%)
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(GREEN) O------------------------/
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The hold device will only work if you hang up the phone. To make a hold/mute
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switch, run a short wire across to create a short circuit (who cares if you
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damage CO equipment?).
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CONCLUSION:
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I hope that you have enjoyed this installment of Basic Telecommunications.
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I have assumed that you have read the first four in this series, and also that
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you have a basic knowledge of electronics. In Basic Telecommuications Part VI,
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we will discuss fortress fones (pay phones).
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{G-Files} Command <?>:
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