HPAVC/HPAVC CD-ROM.iso/BIOC5_TX.ZIP/BIOC5_TX.TXT

Text File | 1993-06-18 | 16KB | 329 lines

               *******BIOC AGENT 003 COURSE IN********
               *                                     *
               *      ==========================     *
               *      =BASIC TELECOMMUNICATIONS=     *
               *      ==========================     *
               *                PART V               *
                ***************************************


PREFACE:

PREVIOUS INSTALLMENTS OF THIS SERIES WERE 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."

WIRING:
-------

ASSUMING A STANDARD ONE-LINE FONE, THERE ARE USUALLY 4 WIRES THAT LEAD OUT OF
THE FONE SET.  THESE ARE STANDARDLY COLORED RED, CREEN, YELLOW, & BLACK.  THE
RED & GREEN SIRES 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 MODULE9.

IN TELEPHONY, THE RED & GREEN WIRES ARE OFTEN REFERRED TO AS TIP (T) & RING
(R).  THE TIP IS USUALLY 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 (AKA DIAL OR PULSE) WILL WORK FINE REGARDLESS 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
RECTIFIER BRIDGE WHICH COMPENSATES FOR POLARITY REVERSAL.]  THIS I WHY UNDER
CERTAIN (NON-DIGITAL) SWITCHILG 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 GENERARTED.

VOLTAGES, ETC.
--------------

WHEN YOUR TELEPHONE IS ON-HOOK (IE, HUNG UP) THERE IS APPROXIMATELY 48 VOLTS
OF DC CURRENT (VDC) FLOWING THROUGH 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 13 VOLTS.  THE RESISTANCE OF THE
LOOP ALSO DROPS BELOW THE 2500 OHM LEVEL.

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 VOLTAGE (& RESISTANCE) DROP 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 PARTIES 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 PERSUED.  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.

THE FOLLOWING ARE INSTRUCTIONS ON HOW TO BUILD A SIMPLE BLACK BOX.  OF COURSE
, ANYTHING THAT PREVENTS THE VOLTAE FROM DROPPING WOULD WORK.

YOU ONE OR 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 THE 2 SCREWS ON THE NETWORK BOX LABELED >F<
AND >RR<.  WRAP THE RESISTOR BETWEEN THE 2 SCREWS MAKING SURE THAT IT DOESN'T
TOUCH ANY OTHER TERMINALS!.  NOW CONNECT ONE WIRE FROM THE SWITCH TO THE RR
TERMINAL.  FINALLY, ATTACH THE REMAINING WIRE TO THE GREEN 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 FREE.

WHEN YOUR PHRIENDS CALL (AT A PREARRANGED TIME), QUICKLY LIFT & DROP THE
RECEIVER AS FAST A POSSIBLE.  THIS WILL STOP THE RINING (DO IT AGAIN IF IT
DOESN'T) WITH OUT STARTING THE BILLING.  IT IS IMPORTANT THAT YOU DO IT
QUICKLY (LESS THAN ONE SECOND THEN PUT THE SWITCH IN THE FREE POSITION AND
PICK UP THE FONE.  KEEP ALL CALL SHORT AND PREFERRABLY UNDER 15 MINUTES.

NOTE:  IF ANYONE PICKS UP AN EXTENSION IN THE CALLED PARTIES HOUSE AND THAT
FONE IS NOT SET FOR FREE THEN BILLING WILL START.

NOTE #2:  AN OLD WAY OF SIGNADLING 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**   *                    !
!                *                    !
!            REISTOR                  !
!                *                    !
!                *                    !
!              >RR<*******SWITCH****  !
!                                  *  !
****GREEN WIRE**********************  !
!                                     !
---------------------------------------

NOTE:  THE BLACK BOX WILL NOT WORK UNDER ESS OR OTHER SIMILAR DIGITAL
SWITCHES SINCE ESS DOE NOT CONNECT THE VOICE CIRCUITS UNTIL THE FONE IS
PICKED UP (& BILLING STARTS).  INSTEAD, ESS USES AN "ARTIFICIAL" COMPUTER
GENERATED RING.

RINGING:
--------

TO INFORM A SUBSCRIBER OF AN INCOMING CALL, THE TELCO SENDS 90 VOLTS (RMS) OF
AC CURRENT DOWN THE LINE (AT AROUND 15 TO 60 HZ)  IN STANDARD FONES, THIS
CAUES 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.  A REGULAR 60
WATT LIGHT BULB CAN ALSO BE HOOKED UP USING A SIMPLE (120 VAC) RELAY.

WARNING:  90 & 120 VAC 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 TO PREVENT THE DC CURRENT
FROM INTERFERRING WITH THE BELL [A CAPACITOR WILL PASS AC CURRENT WHILE IT
WILL PREVENT DC CURRENT FROM FLOWING (BY STORING IT)].

ANOTHER REASON THAT THE TELCO HATES BLACK BOXES IS BECUASE RINGING USES ALOT
OF COMMON-CONTROL EQUIPEMET, IN THE CO, WHICH USE ALOT 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 MAY BE
CONSTRUED AS SUSPICIOUS.  SOME OFFICES MAY BE SET UP 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 TAKE THE
VOLTAGE READINGS ON YOUR FONE LINE [ANY SIMPLE MULTI-TESTER (A MUST) WILL DO.
] PHREAKING IS AN INTERACTIVE PROCESS NOT A PASSIVE ONE!

DIALING:
--------

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
(MAKING) THE LOCAL LOOP ONCE FOR EVERY DIGIT DIALED.  SINCE THE PHYSICAL
CONNECTION MUQT 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, THERE ARE 10 PULES PER SECOND (MAX).  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) BREAK PERIOD AND A 40 MS
MAKE PERIOD.  (60+40=100 MS = 1/10 MINUTE).  THIS IS REFERRED TO AS A 60%
BREAK INTERVAL.  SOME OF THE MORE SOPHISTICATED ELECTRONIC FONES CAN SWITCH
BETWEEN A 60% & A 67% BREAK INTERVAL.  THIS IS DUE TO THE FACT THAT MANY
FOREIGN NATIOS USE A 67% BREAK INTERVAL.

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 DIALIN 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 NOISES 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) YO 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 CLOES 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 UPTO PAR WITH MODERN DAY SWITCHING
EQUIPMENT (SUCH AS ESS) SINCE PULSE DIALING WAS DESIGNED TO ACTUALLY MOVE
RELAYS BY THE NUMBER OF DIGITS DIALED (IN SXS OFFICES).

EACH KEY ON A DTMF KEYPAD PRODUCES 2 FREQUENCIES SIMULTANEOUSLY (ONE FROM THE
HIGH GROUP AND ANOTHGR FROM THE LOW GROUP).

          -------------------------
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  !
          !     !     !     1     !
          !-----!-----!-----!-----1
          !     ! 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 O 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 AD 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 CONFERENCING.

ACD'S ARE BECOME RARE THOUGH.  YOU WILL PROBABLY HAVE TO MAKE SEVERAL NPA-555
-1212 CALLS BEFORE YOU FIND ONE.

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) AD PLANS CAN BE FOUND IN TAP AS WELL AS ON MANY BBS'S.


TRANSMITTER/RECEIVER:
---------------------

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 CURRENT FLOWING 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.

THE REASON 2 SIRES ARE USED ON THE LOCAL LOOPS ARE BECAUSE IT IS ALOT CHEAPER
FOR THE TELCO.  ALTHOUGH, ALL OF THE INTER-OFFICE TRUNKS UTILIZE 4 WIRES.
THIS IS NECESSARY FOR FULL DUPLEX (IE, SIMULTANEOUS CONVERSATION ON BOTH
SIDES) AND FOR AMPLIFICATION DEVICES.  THERE ARE SIMILAR DEVICES IN THE CO'S,
KNOWN AS A HYBRID, THAT COUPLE THE 4-WIRE TRUNKS TO THE 2-WIRE LOCAL LOOPS
AND VISA-VERSA.

MISCELLANEOUS:--------------

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.

HOLD:

WHEN A TELEPHONE GOES OFF HOOK, THE RESISTANCE DROPS BELOW 2500 OHMS.  AT
THIS POINT, THE TELCO WILL SEND A DIAL TONE.  TO PUT SOMEONE ON HOLD YOU MST
PUT A 1000 OHM RESISTOR (1 WATT) ACROS 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.

*****BIOC
*=$=*AGENT
*****003

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