Jason Aller Floppy Collection/432.img/PHREAK.ZIP/LEARNTON

Text File | 1980-01-01 | 8KB | 317 lines

BUT HOW DOES IT WORK ?



  How much do you really understand about the way your

telephone works?  Probably not as much as you should.

Considering the amount of time most people spend on the

contraptions, this is really quite a disgrace.  Ask questions

and make an effort to learn and you'll be the exception to

the rule, which is basically: "Safety is Stupidy."  Read on.



                   WIRING



  Assuming a standard one-line fone, there are usually 4

wires that lead out of the fone set.  These are standardly

colored red,green,yellow, and black.  The red and green wires

are the two that are actually hooked up to your central

office (CO).  The yellow wire is sometimes used to ring

different fones on a party line (i.e., one number, several

families-found primarily in rural areas where they pay less

for the service and they don't use the fone as much),

otherwise the yellow is usually just ignored.  On some two-

line fones, the red and green wires are used for the first

fone number and the yellow and black are used for the second

line.  In this case there must be an internal or external

device that switches between the two lines and provides a

hold function(such as Radio Shack's outrageously priced 2

line and hold module).

  In telephony, the green and red wires are often referred to

as tip(T)and ring(R), respectively.  The tip is the more

positive of the two wires.  This naming goes back to the old

operator cord boards where one of the wires was the tip of

the plug and the other was the ring (of the barrel).

  A rotary fone (a.k.a. dial or pulse) will work fine

regardless of whether the red (or green) wire is connected to

the tip (+) or ring (-).  A touch-tone fone is a different

story, though.  It will not work except if the tip (+) is the

green wire.  (Some of the more expensive STM fones do have a

bridge rectifier which compensates for polarity reversal,

however.)  This is why under certain (non-digital) switching

equipment you can reverse the red and green wires on a touch-

tone fone and receive free DTMF service.  Even though it

won't break dial tone,reversing the wires on a rotary line on

a digital switch will cause the tones to be generated.



                   VOLTAGES,ETC.



  When your telephone is on-hook (i.e., hung up) there are

approximately 48 volts of DC potential across the tip and

ring.  When the handset of a fone is lifted, a few switches

close which cause a loop to be connected (known as the "local

loop") between your fone and the CO.  Once this happens, DC

current is able to flow through the fone with less

resistance.  This causes a relay to energize which causes

other CO equipment to realize that you want service.

Eventually, you should end up with a dial tone.  This also

causes the 48 VDC to drop down into the vicinity of 12 volts.

The resistance of the loop also drops below the 2500 ohm

level, though FCC licensed telephone equipment must have an

off-hook impedance of 600 ohms.

  As of now, you are probably saying to yourself that this is

all nice and technical but what the hell good is the

information.  Well, also consider that this drop in impedance

is how the CO detects that a fone was taken off hook (picked

up).  In this way, they know when to start billing the

calling number.  Now what do you suppose would happen if a

device such as a resistor or a zener diode was placed on the

"called " party's line so that the voltage would drop just

enough to allow talking but not enough to start billing?

First off, the calling party would not be billed for the call

but conversation could be pursued.  Secondly, the CO

equipment would think that the fone just kept on ringing.

The Telco calls this a "no-no" (toll fraud to be more

specific) while phone phreaks affectionately call this mute a

black box.



            HOW THESE BOXES ARE BUILT



  It's really surprisingly easy to build a device such as a

black box.  If it weren't for the amazingly high morals

inherent in today's society, you'd most certainly see more of

them in use.  Only two parts are needed: an SPST toggle

switch and a 10,000 ohm (10 K),1/2 watt resistor.  Any

electronics store should stock these parts.

  A person would then cut 2 pieces of wire (about 6 inches

long) and attach one end of each wire to one of the terminals

on the switch.  Then the K500 (standard desk fone) would be

turned upside down and the cover taken off.  A wire would be

located and disconnected from its terminal.  The switch would

then be brought out the rear of the fone and the cover

replaced.  Labelling the switch usually comes next.  A

position where one receives a dial tone when picking up is

marked "NORMAL".  The other side is, naturally, "FREE".



            MAKING THEM WORK



  When phriends call (usually at a prearranged time), the

person with the black box quickly lifts and drops the

receiver as fast as possible.  This stops the ringing (if not

it must be done again) without starting the billing.  This

must be done within less than one second.  The phone can then

be picked up with the switch in the "FREE" position.  Most

phone phreaks are wise enough to keep their calls under 15

minutes in length, greatly minimizing the odds of getting

caught.

  Some interesting points:(1) If someone picks up an

extension in the called party's house and that fone is not

set for "FREE", then billing will start.(2) An old way of

signalling a phriend that you want to call him is to make a

collect call to a non-existent person in the house.  Since

the phriend will (hopefully) not accept the charges, he will

know that you are about to call and thus prepare the black

box (or vice versa).(3) The phone company can detect black

boxes if they suspect one on the line.  This is done due to

the presence of AC voice signal at the wrong DC level! (4)

The black box will not work under ESS or other similar

digital switches since ESS does not connect the voice

circuits until the fone is picked up (and billing starts).

Instead, ESS uses an "artifical" computer generated ring.



                  RINGING



  To inform a subscriber of an incoming call, the telco sends

90 volts (PK) of pulsing DC down the line (at around 15 to 60

Hz; usually 20 Hz).  In most fones this causes a metal

armature to be attracted alternately between two electro-

magnets thus striking 2 bells.  Of course, the standard bell

(patented in 1878 by Tom A. Watson) can be replaced by a more

modern electronic bell or signalling device.

  Also, you can have lights and other similar devices in lieu

of (or in conjunction with) the bell.  A simple neon light

(with its corresponding resistor) can simply be connected

between the red and green wires (usually L1 and L2 on the

network box) so that it lights up on incoming calls.

  Be advised that 90 VDC can give quite a shock.  Exercise

extreme caution if you wish to further pursue these topics.

  Also included in the ringing circuit is a capacitor to

prevent the DC current from interfering with the bell (a

capacitor will pass AC and pulsing DC while it will prevent

straight DC from flowing-by storing it).

  Another reason that telcos hate black boxes is because

ringing uses a lot of common-control equipment in the CO,

which use a lot of electricity.  Thus the ringing generators

are being tied up while a free call is being made.  Usually

calls that are allowed to "ring" for a long period of time

will be construed as suspicious.  Some offices may be set up

to drop a trouble card for long periods of ringing and then a

"no-no" detection device may be placed on the line.

  Incidentally, the term "ring trip" refers to the CO process

involved to stop the AC ringing signal when the calling fone

goes off hook.

  It is suggested that you actually dissect fones to help you

better understand them (regardless of whether or not you want

to build any devices).  It will also help you to better

understand the concepts here if you actually prove them to

yourself.  For example, actually take the voltage readings on

your fone line (any simple multi-tester (a must) will do).

Phreaking and/or learning is an interactive process, not a

passive one!