           LOOPS EXPLAINED

          AUTHOR UNKNOWN

	LOOPS OCCUR IN ALL AREA CODES AND CONSIST OF TWO PHONE NUMBERS.
THESE NUMBERS ARE IN THE SAME EXCHANGE AND THE LAST FOUR DIGITS ARE
USUALLY SIMILAR.  A TYPICAL LOOP PAIR LIGHT LOOK LIKE 212-555-9990
AND 555-9Y93.  THERE ARE USUALLY AT LEAST TWENTY LOOPS IN AN AREA
CODE AND OFTEN ALL OF THE LOOPS IN AN AREA CODE WILL HAVE IDENTICAL
SUFFIX PAIRS.
 
	THE BASIC THING ABOUT ANY LOOP IS THAT THE TWO NUMBERS ARE
CONNECTED TOGETHER.  IF I WERE TO CALL ONE NUMBER AND YOU WERE TO
CALL THE OTHER WE'D BE CONNECTED.  IT'S ALL A BIT EERIE AT FIRST
BECAUSE MOST LOOPS DO NOT RING; IF YOU DIAL A LOOP AND THERE IS
SOMEONE ON THE OTHER END YOU WILL BE INSTANTLY CONNECTED.  WHAT WILL
YOU HEAR IF YOU DIAL A LOOP NUMBER AND THERE'S NO ONE ON THE OTHER
END?  THAT DEPENDS UPON WHICH OF THE NUMBERS YOU DIAL.  IF YOU DIAL
THE HIGHER NUMBER OF THE PAIR YOU WILL HEAR ONLY SILENCE; IF YOU DIAL
THE LOWER YOU WILL HEAR A 1000 HZ TONE.  ON MOST LOOPS YOU CAN TALK
TO ONE CALLER AFTER ANOTHER ON T0QzQ!IEND WWOW TWO PEOPLE TO TALK
AND USUALLY SOUND LIKE ANY OTHER PHONE CONNECTION.  YOU MAY BE ASKING
SO WHAT? THE ANSWER TO YOUR QUESTION IS THAT LOOPS OFFER ANONYMITY.
PEOPLE USE THIS ANONYMITY FOR MANY REASONS.

	WE ARE NOW TO THE POINT OF WONDERING WHAT TELCO USES LOOPS FOR.
THERE HAVE BEEN A NUMBER OF THEORIES ADVANCED ON THIS TOPIC OVER THE
YEARS BUT FEW PEOPLE HAVE BOTHERED TO ASK TELCO.  ONE COMMON THEORY
HAS BEEN AKIN TO THE IDEA THAT THE LOOPS ARE SOMEHOW USED TO "TIE UP"
UNUSED PHONE LINES AT THE CENTRAL OFFICE TO "KEEP THEM OUT OF
TROUBLE." (I HAVE ALWAYS ENJOYED THE IMAGE OF TWO LONELY PHONE LINES
TIED TOGETHER TO KEEP THEM COMPANY.)
 
	LOOPS ARE USED TO SAVE TIME AND MANPOWER IN TESTING LONG
DISTANCE TRUNKS.  WE'RE NOT TALKING ABOUT THE PHONE LINE THAT
CONNECTS YOUR PHONE TO THE CENTRAL OFFICE BUT THE TRUNKS THAT CONNECT
CENTRAL OFFICES AND RUN IN LENGTH FROM A FEW THOUSAND FEET TO MANY
MILES.  HOME OR BUSINESS TELEPHONE IS A TTR VOICE AND THE CALLER'S
VOICE IN DIFFERENT DIRECTIONS.  ONCE THE LINE GETS TO TELCO PREMISES
THE SIGNAL IS DIVIDED UP INTO TWO CIRCUITS.  ONE CIRCUIT CARRIES YOUR
VOICE AND THE OTHER CARRIES YOUR CALLER'S VOICE. IF THE SIGNALS WERE
KEPT ON ONE CIRCUIT THERE WOULD BE PROBLEMS WITH FEEDBACK AND ECHOES.
TRUNKS MAY CONSIST OF TWO PAIRS OF TWO WIRE CIRCUITS OR MAY BE RADIO
FREQUENCY CARRIERS ON A CABLE.  TRUNKS HAVE REPEATERS ALONG THE WAY
WHICH AMPLIFY THE SIGNAL REMOVE ECHOES AND EQUALIZE FREQUENCIES.
REPEATERS OCCUR ABOUT EVERY TWO MILES ON AN "OLD STYLE" WIRE TRUNK
LINE AND ABOUT EVERY 2000 FEET ON CARRIER TRUNKS.  VERY SHORT TRUNKS
MAY NOT HAVE A REPEATER. REPEATERS NEED TO BE TESTED AND ADJUSTED
OCCASIONALLY. IN THE OLD DAYS A TECH WOULD TEST A TRUNK BY ARRANGING
FOR SOMEONE TO BE AT THE OTHER END.  HE WOULD THEN SEND A 1000 HZ
TEST TONE TO THE OTHER PERSON WHO WOULD READ THE VOLUME ON A METER.
TO COMPLETE THE TEST THE OTHER TECH SENDS A SIGNAL BACK ON THE OTHER
LEG TO THE FIRST TECH AS THE PHONE SYSTEM GREW TELCO DECIDED TO CUT
DOWN ON MANPOWER BY TYING TWO LINES TOGETHER. THUS THE LOOP WAS BORN.
TRUNKS ARE TIED TOGETHER VIA A THING CALLED A "ZERO LOSS TERMINATOR
WHICH CONNECTS LINES SO THERE IS NO CHANGE IN VOLUME.  BY THE MID
FIFTIES, THE ENTIRE PHONE SYSTEM HAD BEEN EQUIPPED WITH LOOPS, SO A
TECH AT ONE END COULD TEST A TRUNK ALONE BY DIALING A LOOP. HE DIALS
THE OTHER HALF OF THE LOOP WITH A KNOWN GOOD TRUNK. THEN HE REVERSES
THE SIGNAL PATH TO COMPLETE THE TEST.
 
	IT WASN'T LONG BEFORE SOME ORDINARY CITIZENS DISCOVERED THAT
LOOPS COULD ALSO PASS VOICES NOT JUST TONES.  SINCE THE LINES
BELONGED TO TELCO THEY WEREN'T BILLED FOR THE CALL.  SO A FEW PEOPLE
MADE FREE CALLS TO FRIENDS BUT THERE WAS SO LITTLE OF THIS THAT ITS
EFFECT ON THE PHONE COMPANY'S INCOME WAS WAY "DOWN IN THE NOISE." IT
WASN'T UNTIL YEARS LATER IN THE EARLY SEVENTIES THAT BELL WAS TO PUT
BILLING CIRCUITRY ON LOOP NUMBERS.  TO AVOID GIVING AWAY THEIR
LOCATION MOST BOOKIES USED A CHEESEBOX A DEVICE THAT CONNECTS TWO
PHONE LINES TOGETHER.  CHEESEBOXES WERE INSTALLED IN A SMALL BUSINESS
OFTEN A SMALL BUTCHER SHOP OR A GROCERY.  THE BOOKIE ARRANGED WITH
THE PROPRIETOR TO HAVE TWO PHONES INSTALLED IN THE SHOP AND WOULD PAY
A SMALL MONTHLY FEE.  HE THEN TIED THE LINES TOGETHER WITH HIS
CHEESEBOX AND GAVE ONE OF THE NUMBERS TO HIS CLIENTELE. SOME BOOKIES
EITHER COULDN'T AFFORD A CHEESEBOX OR COULDN'T LOCATE ONE AT ANY
PRICE SO THEY HIT UPON USING LOOPS.  IT WAS GOOD WHILE IT LASTED.
GRADUALLY HOWEVER MORE AND MORE SHADY CHARACTERS STARTED USING LOOPS.
THE AUTHORITIES WEREN'T BLIND TO THIS AND STARTED APPROACHING THE
TELCO TO DO TRACES ON THESE LOOPS. EVENTUALLY THE PHONE COMPANY WAS
SPENDING A LOT OF TIME ON CRIMINAL TRACES AND DECIDED TO DO SOMETHING
ABOUT THESE LOOPS.
 
	AROU0b1 =STARTED INSERTING A BANDPASS FILTER THAT PASSED ONLY
1000 HZ IN THE TERMINATOR END OF ITS' LOOPS.  WITH THIS CHANGE TT
BLOCKED VOICES.  WE'RE GOING TO SEE THAT THE SOLUTION WAS ONLY
TEMPORARY THOUGH.  THE OLD STYLE FOUR WIRE TRUNKS COULD ONLY HANDLE
ONE CALL AT A TIME TAKING UP A LOT OF WIRE AND SPACE. THERE HAD TO BE
A WAY TO CRAM CALLS INTO A SMALLER SPACE.  BY THE EARLY 1960'S BELL
HAD STARTED SWITCHING TO CARRIER TRUNKS WHICH PUT MANY CALLS ON A
CABLE.  EACH SIGNAL MODULATED AN AM CARRIER ON A DIFFERENT FREQUENCY.
BECAUSE CARRIER USES RADIO FREQUENCY TRANSMITTERS AND RECEO CRAM
CALLS INTO A SMALLER SPACE.  BY THE EARLY 1960'S BELL HAD STARTED
SWITCHING TO CARRIER TRUNKS WHICH PUT MANY CALLS ON A CABLE.  EACH
SIGNAL MODULATED AN AM CARRIER ON A DIFFERENT FREQUENCY.  BECAUSE
CARRIER USES RADIO FREQUENCY TRANSMITTERS AND RECE   1000 HZ FILTER
SO A SWITCH WAS ADDED TO SWITCH IT ON AND OFF.  NORMALLY THE FILTER
WOULD BE LEFT ON.  WHEN A TECH WISHED TO TEST A TRUNK HE WOULD TURN
THE SWITCH ON BYPASSING THE FILTER.  WHEN HE WAS DONE HE WAS EXPECTED
TO TURN OFF THE SWITCH.  IF HE FORGETS A LOOP WILL CONTINUE TO PASS
VOICE FREQUENCIES UNTIL SSOFF.
 
	LET'S LOOK AT HOW LOOPS ARE USED NOWADAYS.  IF A TECH DIALS UP
THE LOWER NUMBER HE WILL IMMEDIATELY GET A 1000 HZ TONE COMING BACK TO
HIM WHICH IS INJECTED AT A SPECIFIC VOLUME KNOWN AS "ZERO DB" LEVEL.
USING HIS METER HE CAN GAUGE IF THERE ARE ANY PROBLEMS ON THE LINE
AND IF HE NEEDS TO DO A COMPLETE TEST AT VARIOUS FREQUENCIES HE THEN
TURNS THE FILTER BYPASS SWITCH ON.  MOST OF THIS WORK IS DONE AT
NIGHT WHEN REPAIR PEOPLE ARE FREE FROM NORMAL CHORES.
 
	IN PREPARING THIS REPORT I INTERVIEWED SEVERAL SECURITY
DIRECTORS FOR NEW YORK TELEPHONE COMPANY AND SPENT SOME TIME ON LOOPS
TALKING TO PEOPLE WHO USE THEM.  IT TURNS OUT THERE ARE PEOPLE USING
LOOPS FOR MORE THINGS THAN I HAD IMAGINED. I HAVE ALWAYS WONDERED IF
SPIES USE LOOPS BUT I HAVEN'T ENCOUNTERED ANY YET.  WHEN I STARTED
LOOKING INTO LOOPS I WAS AWARE THAT SOME RADIO PIRATES USE LOOPS.
ESPECIALLY IN THE NEW YORK CITY AREA YOU'LL OFTEN RUN INTO AM AND FM
PIRATES ON LOOPS LATE AT NIGHT.
 
	SOME LOCAL LOOP NUMBERS ARE PRETTY WELL KNOWN AND ARE PASSED
AROUND HIGH SCHOOLS AND COLLEGES.  WHEN STUDENTS GET BORED AT NIGHT
OR WANT TO FIND A PARTY THEY CALL A LOOP AND WAIT THERE TILL SOMEONE
ELSE CALLS. IT MAY BE SOMEONE THEY KNOW OR A COMPLETE STRANGER. BUT
IT'S SOMEONE TO TALK TO. THEN THERE ARE THE LOOP HABITUATES.  THEY
REGULARY MEET WITH THEIR CIRCLE OF FRIENDS AND ACQUAINTANCES ON LOOPS
AND TEND TO RESENT STRANGERS ON THEIR LOOPS.  REPRESENTATIVES ARE
QUICK TO POINT OUT THAT LOOPS BELONG TO THE PHONE COMPANY.  ANYONE
ELSE USING THEM IS A TRANSGRESSOR.  SINCE BELL IS THE AGGRIEVED PARTY
IT NEEDN'T HAVE ANY QUALMS ABOUT LISTENING TO LOOPS NOR ABOUT TRACING
CALLERS.  BELL WISHES TO DISCOURAGE PEOPLE FROM USING THEM AND
PERIODICALLY PROGRAMS ITS' BILLING COMPUTER TO LOOK FOR LOOP NUMBERS.
ANY CUSTOMER THUS FOUND IS SENT A CARD POINTING OUT THAT THESE
NUMBERS BELONG TO TELCO. WITH THE EXCEPTION OF THOSE STEALING
SERVICES BELL BECOMES AWARE THAT SOME ONE IS CALLING A LOOP USING A
FAKED CREDIT CARD NUMBER; OR SPRINT OR MCI WILL ASK FOR HELP TRACING
SOMEONE ILLEGALLY STEALING THEIR SERVICES TO CALL A LOOP.  THEN IT'S
A MATTER OF WAITING FOR THE PERSON TO TRY AGAIN AND TRACING THE CALL.
IN THESE AFFAIRS THE PHONE COMPANY IS VERY AGGRESSIVE AND EFFECTIVE
IN TRACKING DOWN OFFENDERS.  BELL HAS SOME VERY WELL TRAINED PEOPLE
WHO ARE MOST ADEPT AT KEEPING THE OFFENDER ON THE LINE UNTIL A TRACE
IS COMPLETE.
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