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From: npl@mozart.att.com (Nickolas Landsberg)
Newsgroups: comp.dcom.telecom
Subject: Re: Cleaning Pulses
Message-ID: <9793@accuvax.nwu.edu>
Date: 16 Jul 90 16:18:39 GMT
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X-Telecom-Digest: Volume 10, Issue 489, Message 6 of 10


In article <9677@accuvax.nwu.edu> Andrew Houghton writes:

>In brief, I have heard that at one time AT&T sent out "cleaning
>pulses" in the wee hours of morning to "fuse shorts in the line."

>Assuming this is drivel, is there any basis for such a thing?

>Just wondering,

This comes up periodically, so let me dust off the old brain cells
and try to come up with a semblance of the truth -

All(?) Electronic switches and most electro-mechnical switches can be
programmed to run a test or series of tests on the subscriber loop.
Generically, these are called Automatic Line Insulation Tests (ALIT).
There are three types of tests which may be performed: FEMF (Foreign
EMF, a.k.a. Cross Battery), SRG (Short and Ring Ground), and TRG (Tip
and Ring Ground).  The one which I am most familiar with (being an old
Outside Plant type) is the FEMF.  In theory, especially if paper
insulated cable is still in use, any moisture in the cable will
condense at night and reduce the insulation resistance.  Moisture will
tend to congregate at a low spot in the cable, thus reducing the
resistance of a number of subscriber pairs at once.  This argument is
probably specious in PIC (Plastic/polyethelene ? Insulated Cable.

Running the tests also competes with providing dial-tone, thus, the
switches are programmed to run the test at night.

The telephone number of lines which failed the test are printed out on
the maintenance channel of the switch.  In some companies, this
channel is also monitored by yet another computer system which
translates the telephone number to cable & pair, and, in some cases
performs yet another test to verify that the condition is still there.

The voltage applied during testing has nothing to do with "cleaning
pulses" or to "fuse shorts on the line."  About the only thing I saw
which would "fuse shorts" is a "630" set. (630 Volts DC applied to the
line.)  P.S.  Does anyone know if these are still in use?  It's been
years since I left the Outside Plant Dept.


Nick Landsberg