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TUCoPS :: Phreaking General Information :: bioc5.txt

BIOC Agent 003's Basic Telecom Tutorial 5 of 7

*******BIOC Agent 003's course in******
*                                     *
*      ==========================     *
*      ==========================     *
*                PART V               *
    Brought to you by Zyolog ZCBBS
Revised:  08-AUG-84
     Previous installments of this
series here focused on telephony from a
Network point-of-view.  Part V will
deal with telephone electronics
focusing primarily on the subscriber's
telephone.  Hereinafter simply referred
to as "fone."
     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, & black.
The red & green wires are the two that
are actually hooked up to your CO.  The
yellow wire is sometimes used to ring
different fones on a party line (ie,
one #, 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 & green wires
are used for the first fone # and the
yellow & 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 & hold module).
     In telephony, the green & red
wires are often referred to as tip (T)
& ring (R), respectively.  The tip is
the more positive of the two wires.
This naming gere one of the wires was
the tip of the plug and the other was
the ring (of the barrel).
     A rotary fone (aka dial or pulse)
will work fine regardless of whether
the red (or green) wire is connected
the tip(+) or ring(-).  A touch-tone
(TM) fone is a different story, though.
It will not work except if the tip(+)
is the green wire. [Although, some of
the more expensive DTMF fones do have a
bridge rectifier which compensates for
polarity reversal.] This is why under
certain (non-digital) switching
equipment you can reverse the red &
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
Voltages, Etc.
     When your telephone is on-hook
(ie, hung up) there is approximately 48
volts of DC potential across the tip &
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 & 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
ahands of our "friends" at D&B. To say
the least, they weren't exactly
thrilled about it. In fact, they did
not even believe that they had a
security problem! (Well, that just goes
to prove that if you are good, no one
knows that you are there!)
     In a big effort to defeat us, they
called in an outside service to spruce
up their "security." Well, fortunately
for us, we were able to find out about
the new system! (Which wasn't really a
problem. First, they had the new
dial-ups when you logged on, and as
always they have a nice little place on
Telenet! (Where we do most of our work:
C 20188).
     Now, they have set up a new system
they like to call DunsNet.  They are
trying to pass it off as a ectionately
call this mute a black box.
     The following are instructions on
how to build a simple black box.  Of
course, anything that prevents the
voltage from dropping would work.
     You only need two parts: A SPST
toggle switch and a 10,000 ohm (10 K),
1/2 watt resistor.  Any electronics
store should stock these parts.
     Now, cut 2 pieces of wire (about 6
inches long) and attach one end of each
wire to one of the terminals on the
switch.  Now turn your K500 (standard
desk fone) upside down and take off the
cover. Locate wire (disconnect it from
its terminal).  Now bring the switch
out the rear of the fone and replace
the cover.
     Put the switch in a position where
you receive a dial tone.  Mark this
position NORMAL.  Mark the other side
     When your phriends call (at a
prearranged time), quickly lift & drop
the receiver as fast a possible.  This
will stop the ringing (do it again if
it doesn't) with out starting the
billing.  It is important that you do
it quickly (less than 1 second). Then
put the switch in the FREE position and
preferrably under 15 minutes.
NOTE: If someone picks up an
      extension in the called parties
      house and that fone is not set
      for FREE then billing will
NOTE: An old way of signalling a
      phriend that you are about to
      call is making a collect call to
      a non-existant person in the
      house.  Since your friend will
      not accept the charges, he will
      know that you are about to call
      and thus prepare the black box
      (or visa versa).
WARNING: The Telco can detect
         black boxes if they suspect one
         on your line.  This is done due
         to the presence of AC voice
         signal at the wrong DC level!
Pictoral Diagram:
(Standard Rotary K500 fone)
!                                     !
***BLUE WIRE**>>F<                    !
!            *   *                    !
**WHITE WIRE**   *                    !
!                *                    !
!            RESISTOR                 !
!                *                    !
!                *                    !
!              >RR<*******SWITCH****  !
!                                  *  !
****GREEN WIRE**********************  !
!                                     !
NOTE: 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 (& billing
      starts).  Instead, ESS uses an
      "artificial" computer generated
     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 signaling 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 & green wires (usually
L1 & L2 on the network box) so that it
lights up on incoming calls.
WARNING: 90 VDC can give quite a shock
         Exercise extreme caution if
         you wish to further persue
         these topics.
     Also included in the ringing
circuit is a capacitor tbig savings of
time since the hassle of using a a time
shared public network does not exist.
We're sure that Mr. J.W.P. of DUNSPRINT
had more on his mind when he wrote the
letter (on the system)! DunsNet is
accessible from a regular dial-up.  We
have not been able to get a number yet
for this system, but once on it
allegedly works just like Telenet! Two
carriage returns and you will see
"DunsNet" then the familiar "@" symbol.
To use the system like we showed you,
type "RPTS" at thiup to drop a trouble
card for long periods of ringing 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.
NOTE: It is suggested that you
      actually dissect fones to help
      you better understand them. It
      will also help you to better
      understand the concepts here if
      you actually prove them to
      yourself.  For example, actually
      the line [any simple
      multi-tester (a must) will do.]
      Phreaking is an interactive
      process not a passive one!
     On a standard fone, there are two
common types of dialing: pulse & DTMF.
Of course, some people insist upon
being different and don't use the DT
thus leaving them with MF (Multi
Frequncy, aka operator, blue box)
tones.  This is another "no-no" and the
Telco Security gentelmen have a special
knack for dealing with such "phreaks"
on the network.
     When you dial rotary, you are
actually rapidly breaking &
reconnecting (breaking & making) the
local loop once for each digit dialed.
Since the physical connection must be
broken, you cannot dial if another
extension (of that #) is off-hook.
Neither of the fones will be able to
dial pulse unless the other hangs up.
     Another term often referred to in
telephone electronics is the break
ratio.  In the US, the standard is 10
pulses per second.  When the circuit is
opened it is called the break interval.
When it is closed it is called the make
interval.  In the US, there is a 60
millisecond (ms) make period and a 40
ms break period. (60+40=100 ms = 1/10
second).  This is referred to as a 60%
make interval.  Some of the more
sophisticated electronic fones can
switch between a 60% & a 67% make
interval.  This is due to the fact that
many foreign nations use a 67% break
     Have you ever been in an office or
a similar facility and saw a fone
waiting to be used for a free call but
some asshole put a lock on it to
prevent outgoing calls?
     Well, don't fret phellow phreaks,
you can simulate pulse dialing by
rapidly depressing the switchook.  (If
you depress it for longer than a second
it will be construed as a disconnect.)
By rapidly switchooking you are causing
the local loop to be broken & made
similar to rotary dialing! Thus if you
can manage to switchook rapidly 10
times you can reach an operator to
place any call you want! This takes
alot of practice, though.  You might
want to practice on your own fone
dialing a friend's # or something else.
Incidentally, this method will also
work with DTMF fones since all DTMF
lines can also handle rotary.
     Another problem with pulse dialing
is that it produces high-voltage spikes
that make loud clicks in the earpiece
and cause the bell to "tinkle." If you
never noticed this then your fone has a
special "anti-tinkle" & earpiece
shorting circuit (most do).  If you
have ever dissected a rotary fone (a
must for any serious phreak) you would
have noticed that there are 2 sets of
contact that open and close during
pulsing (on the back of the rotary dial
under the plastic cover).  One of these
actually opens and closes the loop
while the other mutes the earpiece by
shorting it out.  The second contacts
also activates a special anti-tinkle
circuit that puts a 340 ohm resistor
across the ringing circuit which
prevents the high voltage spikes from
interferring with the bell.
     Dual Tone Multi Frequency (DTMF)
is a modern day improvement on pulse
dialing in several ways.  First of all,
it is more convenient for the user
since it is faster and can be used for
signaling after the call is completed
(ie, SCC's, computers, etc.).  Also, it
is more up to par with modern day
switching equipment (such as ESS) since
pulse dialing was designed to actually
move ESS offices).
     Each key on a DTMF keypad produces
2 frequencies simultaneously (one from
the high group and another from the low
Low Group !  Q  ! ABC ! DEF !     !
   697 Hz-!  1  !  2  !  3  !  A  !
          !     !     !     !     !
          ! GHI ! JKL ! MNO !     !
   770 Hz-!  4  !  5  !  6  !  B  !
          !     !     !     !     !
          ! PRS ! TUV ! WXY !     !
   852 Hz-!  7  !  8  !  9  !  C  !
          !     !     !     !     !
          !     ! OPER!     !     !
   941 Hz-!  *  !  0  !  #  !  D  !
          !     !  Z  !     !     !
           1209  1336  1477  1633
             (High Group--in Hz)
     A portable DTMF keypad is known as
a white box.
     The fourth column (1633 Hz) is not
normally found on regular fones but it
does have several special uses.  For
one, it is used to designate the
priority of calls on AUTOVON, the
military fone network.  These key are
called: Flash, Immediate, Priority, &
Routine (with variations) instead of
ABCD.  Secondly, these keys are used
for testing purposes by the Telco.  In
some area you can find loops as well as
other neat tests (see Part II) on the
555-1212 directory assistance exchange.
For this, you would call up an DA in
certain areas [that have an Automatic
Call Distributor (ACD)] and hold down
the "D" key which should blow the
operator off.  You will then hear a
pulsing dial tone which indicates that
you are in the ACD internal testing
mode.  You can get on one side of a
loop by dialing a 6.  The other side is
7.  Some phreaks claim that if the
person on side 6 hangs up, occasionally
the equipment will screw up and start
directing directory assistance calls to
the other side of the loop.  Another
alleged test is called REMOB which
allows you to tap into lines by
entering a special code followed by the
7 digit number you want to monitor.
Then there is the possibility of mass
     ACD's are become rare though.  You
will probably have to make several
NPA-555-1212 calls before you find
     You can modify regular fones quite
readily so that they have a switch to
change between the 3rd and 4th columns.
This is called a silver box (aka grey
box) and plans can be found in Tap as
well as on many BBS's.
     When you talk into the
transmitter, the sound waves from your
voice cause a diaphragm to vibrate and
press against the carbon granules (or
another similar substance).  This
causes the carbon granules to compress
and contract thus changing the
resistance of the DC coupled path
through it.  Therefore, your AC voice
signal is superimposed over the DC
current of the local loop. The receiver
works in a similar fashion where the
simple types utilize a magnet,
armature, & diaphragm.
Hybrid/Induction Coil:
     As you may have noticed, there are
two wires for the receiver and two for
the transmitter in the fone, yet the
local loop consists of 2 wires instead
of 4.  This 4-wire to 2-wire conversion
is done inside the fone by a device
known as an induction coil which uses
coupling transformers.  All of the
internal Telco trunks also use 4 wires.
It is only the local loop that uses 2
since it is c converts between 4 and 2
wire set-ups similar to the induction
coil inside the fone. Special data
transmission lines require extremely
low signal to noise ratios, they
require the full four wires--two for
transmission and two for receiving
(even on the local loop).
     In the telephone, there is also a
balancing network consisting of a few
capacitors & resistors which provide
sidetone.  Sidetone allows the caller
to hear his own volume in the receiver.
He can then adjust his voice
accordingly.  This prevents people from
shouting or speaking too softly without
noticing it.
     When a telephone goes off hook,
the resistance drops below 200 ohms.
At this point, the Telco will send a
dial tone.  To put someone on hold you
must put a 1000 ohm resistor (1 watt)
across the Tip & Ring before it reaches
the switchook.  In this way, when the
fone is hung up (for hold) the
resistance remains below 2500 ohms
which causes the CO to believe that you
are still off-hook.  You can build a
simple hold device using the following
pictoral diagram:
    (RED) O-------------------------/
    [L1]       !             !      !
               !             !      !
           1000 Ohm          !      !
           Resistor       Ringing   !
               !          Circuit   !
               !             !      !
               /             !  Switch-
              / SPST Switch  !   Hook
               !             !      !
               !             !      !
               !             !      !/
   (GREEN) O------------------------/
                      --> To Rest of
     This hold device is only effective
if you also hang up the fone.  To make
a hold/mute switch, simple connect a
wire in place of the 1K resistor to
effect a short circuit (who cares if
you damage CO equipment?).
NOTE: Many of the electronics
      components of normal fones
      (K500) are enclosed in the
      network box (which shouldn't be
     I have assumed that the reader has
a basic knowledge of electronics.
Also, I have assumed that you have read
the 4 previous installments of this
series (and hopefully enjoyed them).
     In part VI, we will take a look at
fortress fones.
Suggested Further Reading:
     Electronics Courses A-D, TAP, @
$.75 each.
     Electronic Telephone Projects,
A.J. Caristi, Howard Sams Books.
     Everything you Always Wanted to
Know About 1633 Hz Tones but Were
Afraid to Ask, The Magician, TAP, issue
     Free BELL phone calls, TAP, Fact
sheet #2, @ $.50.
     Free GTE phone calls, TAP, Fact
sheet #3, @ $.50.
     How to modify your Bell Touch Tone
Fone to..
     TAP/Room 603/147 W 42 St./New
York, NY 10036.  Please specify by
backissue #'s (not article names).  All
back-issues are $1 each.  Subscriptions
are $10/year (10 issues). Say that BIOC
Agent 003 sent you.
Another good phreak publication:
     2600/Box 752/Middle Island, NY
11953. Subscriptions are $10/year.
Backissues are $1 each.
*****BIOC             (P) 1984 BIOC
*=$=*Agent            International
July 18, 1984
           <<=-FARGO 4A-=>>
The Bunker     -=:>303-466-2672<:=-
[606 LINES]

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