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Path: utzoo!mnetor!seismo!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: comp.dcom.modems
Subject: Re: What number am I calling from?
Message-ID: <1502@kitty.UUCP>
Date: Sun, 28-Dec-86 13:11:57 EST
Article-I.D.: kitty.1502
Posted: Sun Dec 28 13:11:57 1986
Date-Received: Sun, 28-Dec-86 21:37:08 EST
References: <750@sdcc12.ucsd.EDU> <1706@sunybcs.UUCP> <722@cooper.UUCP> <2263@well.UUCP>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 109
Summary: More details on ANAC, transmission and noise test lines

In article <2263@well.UUCP>, rab@well.UUCP (Bob Bickford) writes:
> >   	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.
> 
>    Why?  I'm afraid my imagination does not present me with any
> compelling reason to belive this a 'security risk'.  Certainly it
> is of little or no use to a telco cracker.

	Well, I guess I have to spell it out...  The availability of ANAC
at any outside plant location (like cross-connect terminal) is of significant
value to anyone bent upon unlawful wiretapping.  Telephone company security
personnel are always concerned about unauthorized persons obtaining any
information with respect to subscriber line pair identity and circuit
routing.  In fact, in New York State it is a specific criminal offense
(Penal Law 250.30) for an "unauthorized" person to obtain "information
concerning identification or location of any wires, cables, lines, terminals
or other apparatus used in furnishing telephone or telegraph service".
	Since people are reporting unrestricted ANAC in California, perhaps
life there is more permissive. :-)

> > 	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).
> 
>    Ours are 8 seconds and 2 seconds; the tone by the way is 1004 Hz
> and NOT 1000 Hz.

	Traditionally, the milliwatt reference frequency was 1,000 Hz, and
still is 1,000 Hz in many central offices (especially those that are still
electromechanical).
	Interestingly enough, the milliwatt reference frequency has been
changed in some areas to 1,004 Hz because of small measurement errors which
occur when measuring through PCM (i.e., digital) CO's or transmission
(T-carrier) facilities.  The reason is that 1,000 Hz is an even divisor of
the 8,000 Hz PCM sampling rate, and any frequency within say 1 Hz of 1,000
Hz exhibits erratic results (to a minor degree, however) during measurement.

> > 	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.
> 
>    Quite true.  We wasted several weeks working on the audio portion of
> our video conferencing system when I was at Vitalink Communications.
> Finally we purchased a Halcyon tester (don't recall model #) and
> stopped listening to the linemen who kept insisting that the line was
> a 600 ohm line.

	There is a good moral to be learned here: Don't ever accept as
gospel any transmission-related information given by telephone company
craftspersons (also salespersons!) - either get it from someone that you
_know_ is an engineer, or measure it yourself.  Not that I have anything
against non-engineers, but many telephone company craftspersons just follow
orders and directions, with little or no understanding beyond that.  For
example, even a craftsperson using a TTS to make transmission measurements
will have _explicit_ instructions how to set the controls on his TTS and
then get a meter reading - but more often than not, will have no idea why
the TTS is operated as he has it configured.

> > 	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".
> 
>    That's strange, we seem to only have one variety of quiet line around
> here, and that's the terminated one.

	You might not know the numbers for the others.  Actually, there may
be TWO lines with balanced terminations (in addition to one for open-circuit
and one for short-circuit).
	Many CO's use a CLA (combined loop-around) for a milliwatt test line.
The CLA uses two sequential numbers (common example 9911 and 9912 applied to
New York Telephone) which work as follows:

1.	Dialing _only_ the 9911 number gives you milliwatt tone.

2.	Dialing _only_ the 9912 number gives you a balanced termination.

3.	Dialing _both_ 9911 and 9912 gives you a bridged connection between
	the two lines whose insertion loss is the typical CO switching loss	
	(usually well under 1.0 dB).  This is referred to as "loop-around"
	mode, and is used for remote transmission measurements to and from
	a CO; its primary purpose is to test interoffice trunks, and it has
	no usefulness for subscriber loop meqsurements.  Many newer CO's have
	a speech energy detector on the CLA which drops the connection if
	_other_ than SF tones are sent in loop-around mode; this has been
	implemented to stop "unauthorized" people from using the CLA for
	talking. 

	So, in addition to the balanced termination available through the CLA,
most CO's still have a short-circuit termination (typical 9954 suffix for
New York Telephone), an open-cicruit termination (typical 9955) and another
balanced termination (typical 9956).
	Note that in addition to a milliwatt line being available through
the CLA (9911 as above), there is usually a dedicated milliwatt line (typical
number is 9910).  There is generally an important distinction between this
apparent duplication of test lines: the CLA is used primarily for interoffice
trunk measurements, so its impedance is 600 ohms - whereas all of the other
lines have 900 ohm impedance.

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