124 lines
8.7 KiB
Plaintext
124 lines
8.7 KiB
Plaintext
-- Note: This file arrived at ARGH garbled; I edited it to remove the
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garbage. If anyone has a better version, please send it to either 201@3464
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WWIVNet or C579380@MIZZOU1.MISSOURI.EDU. (11/92)
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-------------------------------------------------------------------------------
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LOOPS EXPLAINED
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Loops occur in all area codes and consist of two phone numbers. These
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numbers are in the same exchange and the last four digits are usually
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similar. A typical loop pair light look like 212-555-9990 and 555-9993.
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There are usually at least twenty loops in an area code and often all of
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the loops in an area code will have identical suffix pairs. The basic
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thing about any loop is that the two numbers are connected together. If I
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were to call one number and you were to call the other we'd be connected.
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It's all a bit eerie at first because most loops do not ring; if you dial a
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loop and there is someone on the other end you will be instantly connected.
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What will you hear if you dial a loop number and there's no one on the other
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end? That depends upon which of the numbers you dial. If you dial the
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higher number of the pair you will hear only silence; if you dial the lower
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you will hear a 1000 HZ tone. On most loops you can talk to one caller
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after another on ! i end wwow two people to talk and usually sound
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like any other phone connection. You may be asking so what? The answer to
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your question is that loops offer anonymity. People use this anonymity for
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many reasons.
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We are now to the point of wondering what telco uses loops for. There
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have been a number of theories advanced on this topic over the years but
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few people have bothered to ask telco. One common theory has been akin to
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the idea that the loops are somehow used to "tie up" unused phone lines at
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the central office to "keep them out of trouble." (I have always enjoyed
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the image of two lonely phone lines tied together to keep them company.)
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Loops are used to save time and manpower in testing long distance trunks.
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We're not talking about the phone line that connects your phone to the
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central office but the trunks that connect central offices and run in
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length from a few thousand feet to many miles. Home or business telephone
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lines are dwarfed by the much larger trunks. The trunk carries your voice
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and the caller's voice in different directions. Once the line gets to telco
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premises the signal is divided up into two circuits. One circuit carries
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your voice and the other carries your caller's voice. If the signals were
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kept on one circuit there would be problems with feedback and echoes.
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Trunks may consist of two pairs of two wire circuits or may be radio
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frequency carriers on a cable. Trunks have repeaters along the way which
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amplify the signal remove echoes and equalize frequencies. Repeaters occur
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about every two miles on an "old style" wire trunk line and about every
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2000 feet on carrier trunks. Very short trunks may not have a repeater.
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Repeaters need to be tested and adjusted occasionally. In the old days a
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tech would test a trunk by arranging for someone to be at the other end.
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He would then send a 1000 hz test tone to the other person who would read
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the volume on a meter. To complete the test the other tech sends a signal
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back on the other leg to the first tech as the phone system grew telco
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decided to cut down on manpower by tying two lines together. Thus the loop
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was born. Trunks are tied together via a thing called a "zero loss
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terminator" which connects lines so there is no change in volume. By the
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mid fifties, the entire phone system had been equipped with loops, so a tech
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at one end could test a trunk alone by dialing a loop. He dials the other
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half of the loop with a known good trunk. Then he reverses the signal path
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to complete the test. It wasn't long before some ordinary citizens
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discovered that loops could also pass voices not just tones. Since the
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lines belonged to telco they weren't billed for the call. So a few people
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made free calls to friends but there was so little of this that its effect
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on the phone company's income was way "down in the noise." It wasn't until
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years later in the early seventies that Bell was to put billing circuitry on
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loop numbers. To avoid giving away their location most bookies used a
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cheesebox, a device that connects two phone lines together. Cheeseboxes
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were installed in a small business often a small butcher shop or a grocery.
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The bookie arranged with the proprietor to have two phones installed in the
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shop and would pay a small monthly fee. He then tied the lines together
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with his cheesebox and gave one of the numbers to his clientele. Some
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bookies either couldn't afford a cheesebox or couldn't locate one at any
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price so they hit upon using loops. It was good while it lasted. Gradually
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however more and more shady characters started using loops. The authorities
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weren't blind to this and started approaching the telco to do traces on
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these loops. Eventually the phone company was spending a lot of time on
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criminal traces and decided to do something about these loops.
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Around ???? Bell started inserting a bandpass filter that passed only 1000 hz
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in the terminator end of its loops. With this change they blocked voices.
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We're going to see that the solution was only temporary though. The old style
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four wire trunks could only handle one call at a time taking up a lot of
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wire and space. There had to be a way to cram calls into a smaller space.
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by the early 1960's bell had started sw itching to carrier trunks which put
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many calls on a cable. each signal mod ulated an am carrier on a different
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frequency. because carrier uses radio frequency transmitters and receo cram
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ca lls into a smaller space. by the early 1960's bell had started sw
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itching to carrier trunks which put many calls on a cable. each signal mod
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ulated an am carrier on a different frequency. because carrier uses radio
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frequency transmitters and rece1000 hz f ilter so a switch was added to
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switch it 'on and off. normally the filter would be left on. when a tech
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wished to test a trunk he would turn the sw tch on bypas sing the filter.
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when he was done he was expected to turn off the switch. i f he forgets a
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loop will continue to pass voice frequencie until ssoff. let's look at
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how loops are used nowada ys. if a tech dials up the lower number he will
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immediately ge a 1000 hz tone coming back to him which is injected at a
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specific volume known as "zero db" level. using his meter he can gauge if
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there are any problems on the line and if he needs to do a complete test at
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various frequencies he then turns the filter bypass switch on. most of
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this work is done at night when repair people are free from normal chores.
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in preparing this report i interviewed several security directors for new
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york telephone company and spent some time o n loops talking to people who
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use them. it turns out there are people us ing loops for more things than i
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had imagined. i have always wondered if spi es use loops but i haven't
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encountered any yet. when i started looking into l oops i was aware that
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some radio pirates use loops. especially in the n ew york city area you'll
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often run into am and fm pirates on loops late at night. some local loop
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numbers are pretty well known and are passed around high schools and
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colleges. when students ge t bored at night or want to find a party they
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call a loop and wait there t ill someone else calls. it may be someone they
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know or a complete strange r. but it's someone to talk to. then there are
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the loop habituates. they re gulary meet with their circle of friends and
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acquaintances on loops and tend to resent strangers on their loops.
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representatives are quick to point out that loops belong to the phone
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company. anyone else using them is a t ransgressor. since bell is the
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aggrieved party it needn't have any qua lms about listening to loops nor
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about tracing callers. bell wishes to discou rage people from using them
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and periodically programs its' billing comp uter to look for loop numbers.
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any customer thus found is sent a card poin ting out that these numbers
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belong to telco. with the exception of those stea ling services bell becomes
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aware that some one is calling a loop using a fake d credit card number; or
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sprint or mci will ask for help tracing someone illeg ally stealing their
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services to call a loop. then it's a matter of waiting fo r the person to
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try again and tracing the call. in these affairs the phone c ompany is very
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aggressive and effective in tracking down offenders. bell has some very well
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trained people who are most adept at keeping the offen der on the line until
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a trace is complete.
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