The Phreaker's Guide to Loop Lines    otot
courtesy of the Jolly Roger

ot
A loop is a wonderous device which the telephone
company created as test
numbers for telephone
repairmen when testing equipment.
By matching the
tone
of the equipment with the tone
of the loop,
repairmen can adjust and test
the settings
of their telephone
equipment.
ot
A loop,
basically,
consists
of two different telephone
numbers.
Let's
use
A and B as an example.
Normally if you call
A, you will
hear a loud
tone
(this is a 1004
hz tone), and if you call
B, the line will
connect, and
will
be followed by silence.
ot
This is the format
of a loop line.
Now, if somebody calls
A and someone
else
calls
B--Viola!--A and B loop together, and one
connection is made.
Ma Bell
did this so
repairmen can communicate with each other without
having to call
their own
repair
office.
They can also
use
them to exchange
programs, like for
ANA or
Ringback.
Also, many CO's have a "Loop Assignment
Center".
If anyone
has any information on these
centers please tell
me.
ot
Anyway, that
is how a loop is constructed.
From this information,
anyone
can find an actual loop line.
Going back to the A and B example,
Note: the tone
side and the silent
side can be either A or
B.
Don't
be fooled
if the phone
company decides to scramble
them around to
be cute.
otAs you now know, loops come in pairs
of numbers.
Usually,
right after each
other.
oFor
example: 817-972-1890
ot


evev s sand



evev s s817-972-1891


Or, to save space, one
loop line can be written as 817-972-1890/1.
otThis is not always true.
Sometimes, the pattern is in the tens or
hundreds,
and, occaisionally,
the numbers are
random.
otIn cities, usually the phone
company has set aside a phone
number suffix
that
loops will
be used for.
Many different prefixes will
correspond
with that
one
suffix.
otIn Arlington, Texas, a popular suffix for
loops is 1893 and 1894, and
a lot
of prefixes match with them to make
the number.
oFor
Example:  817-460-1893/4
ot


evev s817-461-1893/4
ot


evev s817-465-1893/4
ot


evev s817-467-1893/4
ot


evev s817-469-1893/4
ot


...are
all
loops...
otor a shorter way to write this is:



evev s s817-xxx-1893/4
ot

xxx= 460, 461, 465, 467, 469
otNote: You can mix-and-match a popular suffix with other prefixs in a
city, and almost always find other loops or test numbers.
otNote: For
Houston, the loop suffixes are
1499 and 1799.
And for
Detroit
it's 9996 and 9997.
otWhen there are
a large
number of loops with the same prefix format,
chances are
that
many loops will
be inter-locked.
Using the above example
of Arlington loops again, (I will
write the prefixes to save space) 460, 461,
and 469 are
interlocked
loops.tThis means that
only one
side can be used at
a given time.tThis is because
they are
all
on the same circuit.
otTo clarify, if 817-461-1893 is called, 817-460 and 469-1893 cannot be
called because
that
circuit is being used.tEssentialy,
interlocked
loops
are
all
the same line,
but there are
a variety of telephone
numbers to access
the line.
otAlso, if the operator
is asked
to
break in on a
busy
loop line he/she
will
say that
the circuit is overloaded, or something along those
lines.tThis is because
Ma Bell
has taken the checking equipment
off
the line. 
However, there are
still
many rarely used loops which can
be verfied and can  have emergency calls
taken on them.
otAs you have found out, loops come in many types.tAnother type of loop
is a
filtered loop.tThese
are
loop lines that
the tel co
has put a filter on, so
that
normal
human voices cannot be
heard on either line. 
However, other
frequencies may be
heard.
It
all
depends on what
the tel co
wants the
loop to
be used for.If a loop has gotten to
be very popular with the
local population or used frequently for
conferences, etc.
the tel co
may filter
the loop to
stop
the unwanted "traffic".
Usually,
the filter will
be
removed after a few months, though.

ot


 w wrereheh-----titiononssBrought to
you by the Jolly Roger