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From: larry@kitty.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: What number am I calling from?
Message-ID: <1498@kitty.UUCP>
Date: Thu, 25-Dec-86 13:30:32 EST
Article-I.D.: kitty.1498
Posted: Thu Dec 25 13:30:32 1986
Date-Received: Fri, 26-Dec-86 00:38:09 EST
References: <750@sdcc12.ucsd.EDU> <1706@sunybcs.UUCP> <722@cooper.UUCP> <2247@well.UUCP>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 83
Summary: ANAC, milliwatt test lines, etc.

In article <2247@well.UUCP>, rab@well.UUCP (Bob Bickford) writes:
> >  Here's a bit of phone trivia that works in some places.  Dial
> >  958 and many times you get a generated voice telling you the number
> >  you are DIALING from.
> 
>    Of course, this depends on what particular company's CO equipment
> is being used.  For example, in most of Silicon Valley the magic
> number is 760 although at least one town (can't remember which) uses 890

	The particular test line being described is generally referred to as
ANAC (Automatic Number Announcement Circuit), and is usually found only in
larger metropolitan central offices.  The primary purpose of ANAC is to aid
craftspersons who work on the main distributing frame (MDF) _within_ the
central office, although there is some benefit for outside plant use.  There
are various implementations of ANAC, including one or more of the following:

1.	Dialing a three-digit access code causes the number to be announced
	over a loudspeaker located at the CO MDF; the person dialing the
	acess code hears _nothing_ over the telephone circuit.

2.	Dialing a three-digit access code _followed_ by the seven-digit
	directory number.  A correct match of dialed number and actual
	directory number results in an acknowledgement tone (usually a
	combination of high tone and busy tone).  An _incorrect_ match
	can be optioned to return an announcement of the actual number
	OR be switched to a person within the CO to challenge who is
	using the circuit (n.b. for would-be telephone hackers).

3.	Dialing a three-digit access code which immediately provides an
	announcement over the telephone circuit.  This unrestricted
	implementation has generally been considered a "security" problem
	(use your imagination) by telephone company management; I am
	somewhat surprised to see people posting articles reporting the
	implementation of unrestricted ANAC.

>    More trivia: Most CO's have various service numbers that the
> linemen can dial (from your instrument) to check your level, etc.
> If your exchange is 656, for example, you might find that dialing
> 656-0020 gets you a pulsing 1004 Hz. tone.  It will have been at
> 0 db at the CO; any less is the loss in your line.

	You are referring to milliwatt test lines which provide a 1,000 Hz
signal at 0 dBm (1 mw) into a 900 ohm termination.  Some milliwatt test
lines provide a continuous tone; others have 9 seconds of tone followed by
1 second of silence (with or without answer supervision).
	A word of caution concerning the use of milliwatt test lines: if
you don't know what you are doing and don't have the proper test equipment,
you will be fooling yourself with incorrect measurements.  You need to
properly terminate your telephone line at 900 ohms, and make the measurement
with an electrically isolated meter.  If the 900 ohm termination does not
pass DC, then you will have to use a high-impedance holding coil to keep
the circuit established while making the measurement.  An actual telephone
set is NEVER connected to the line while making the measurement (although
it can be used for dialing, provided the circuit is transfered to a holding
coil during the measurement).
	Note that I said the termination impedance is 900 ohms and NOT
600 ohms.  End office termination impedances (i.e., like your telephone)
are ALWAYS 900 ohms.  Toll offices and intertoll trunks are 600 ohms.
Most dedicated data lines and 4-wire private lines are also 600 ohms.
There is a slight but definite error if 600 ohms is used for subscriber
loop transmission measurement.

>    There are also numbers that give you a terminated line (good
> for balancing bridges) and a sweep tone.

	Almost all CO's provide three "quiet lines" for noise measurement
purposes and repeater test purposes:  (1) a balanced termination; (2) an
open-circuit termination; and (3) a short-circuit termination.  The latter
two lines are primarily used to test negative impedance repeaters for
noise and "singing".
	It is useless to attempt any noise measurement unless (1) you are
certain what type of termination you have dialed; (2) you have a proper
noise measurement test set (which reads in dBRN, among other things); and
(3) you know what you are doing.
	The test line that gives a "sweep tone" is called a "loop checker"
test line.  The amplitude of the tone is NOT constant over the swept
frequency range.  This test line is only useful if you have a loop checker
test set with a properly calibrated meter scale.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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