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Date: Sun, 24 May 87  1:10:34 EDT
From: The Moderator (JSol) <TELECOM-REQUEST@BUIT1.BU.EDU>
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Subject: TELECOM Digest V7 #4
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Resent-Date: Tue, 26 May 87 11:17:41 EDT
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TELECOM Digest     Sun, 24 May 87  1:10:34 EDT    Volume 7 : Issue 4

Today's Topics:

    Submission for comp.dcom.telecom (ALIT and Telephone "Chirps")
 Submission for comp.dcom.telecom (Use of shielded cable for telephones)
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Date: Fri, 22 May 87 23:18:25 EDT
From: kitty!larry@seismo.CSS.GOV
To: seismo!xx.lcs.mit.edu!telecom@seismo.CSS.GOV
Subject: Submission for comp.dcom.telecom (ALIT and Telephone "Chirps")
Cc: kitty!larry@seismo.CSS.GOV


> In a recent article roger@SLEEPY.CS.CORNELL.EDU (Roger Hoover) writes:
> A friend of mine has a cheapo phone that chirps every night at
> 11:55pm.  A call to New York Telephone about this got a response
> claiming that NYT did no regular testing that would cause this.
> A telephone on the same line with a mechanical ringer does not
> make any noise.
>
> 1) What is causing this noise?

	I am willing to bet that the response from New York Telephone is
incorrect.  While the action of New York Telephone test apparatus may be
precipitating the problem, the telephone company has no responsibility
to take any corrective action; such a position may be difficult for the
average customer to accept.  Their "denial" of regular testing is either based
upon specific ignorance of the person to whom you spoke, or is intentionally
based upon paranoia of creating a whole new basis for customer complaints.
The latter situation is probably more likely.
	It sounds to me like the telephone is poorly designed, and causes
the "chirp" whenever telephone line battery voltage is removed and then
reapplied to the telephone when it is on-hook.
	Most telephone company central offices have ALIT (Automatic Line
Insulation Test) apparatus which is used to detect the presence of faulty
outside plant cables.  ALIT apparatus is programmed to test all regular
telephone lines (loop-start only) for low leakage resistance from each
conductor to ground.
	In operation, ALIT apparatus first determines if the line under
test if busy; if it is, the line is not tested.  If the line is idle, the
ALIT apparatus connects to the tip and ring of the line, while DISCONNECTING
the line from the off-hook detection battery source.  The ALIT apparatus
then makes a resistance measurement from tip-to-ground, and ring-to-ground;
such measurements require no central office battery on the line.  The ALIT
apparatus then disconnects from the line and restores it to normal.  The
entire ALIT measurement time is between 1 and 2 seconds per subscriber line.
	Lines which fail the ALIT test (i.e., their leakage resistance to
ground is BELOW a given threshhold), are listed on a printer or transmitted
by other means to a telephone company test center.  Most ALIT apparatus will
also transmit an alarm to an attended test center if a significant number
of lines fail the test.
	So the point is: the most likely explanation for the "chirp" is that
ALIT momentarily disconnects the telephone from the central office battery,
thereby creating a transient voltage which is falsely triggering the "chirp"
circuit in the telephone.  It is also possible that the test voltage from the
ALIT apparatus itself is falsely triggering the "chirp" circuit.
	Since ALIT apparatus can only test lines that are idle, ALIT testing
is always done between 2300 and 0700 hours.  Since ALIT apparatus tests lines
in numerical sequence, the test time of any given line will remain pretty
much the same every night (unless the ALIT apparatus programming is changed).

> 2) Is their an easy way to stop it?

	Buy a better quality telephone. :-)

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|seismo|utzoo}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}    "Have you hugged your cat today?"

------------------------------

Date: Fri, 22 May 87 23:18:45 EDT
From: kitty!larry@seismo.CSS.GOV
To: seismo!xx.lcs.mit.edu!telecom@seismo.CSS.GOV
Subject: Submission for comp.dcom.telecom (Use of shielded cable for telephones)
Cc: kitty!larry@seismo.CSS.GOV

In a recent article dbj@RICE.EDU (Dave Johnson) writes:
> I need to wire a new phone line through a house for use with a modem.
> Is there some kind of sheilded phone cable that I could use to help
> reduce any noise in the connection?  Anything else I should be aware
> of when routing the wire such as not getting too close to electrical
> wires?  Thanks.

	I can think of no valid reason to use shielded telephone cable
for wiring in a house.  Most AC powerline noise is imposed upon telephone
lines through induction rather than conduction or radiation, so any
conventional shielded cable won't help this situation anyhow.
	Furthermore, the relative exposure of inside telephone wiring to
AC powerlines is insignificant when compared to outside cable plant exposure
to the electromagnetic fields of high-voltage AC transmission lines.

	Shielded cable is only useful for high-speed twisted-pair LAN
devices or other high-speed data lines (56 kbits/sec or greater).

	I have only two suggestions for your wiring:

1.	Try to find two-pair "inside station wire" which is _truly_ paired.
	Many two-pair station cables have four wires which are NOT paired,
	and therefore have some susceptibility to noise pickup and crosstalk.
	I wouldn't lose any sleep if you can't find such cable, however.

2.	Try to keep at least a 2 inch separation between telephone cables
	and any powerline wiring.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|seismo|utzoo}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}    "Have you hugged your cat today?"

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End of TELECOM Digest
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