[comp.dcom.telecom] Reverse-voltage Phone Line Test

nazgul@alphalpha.com (Kee Hinckley) (04/08/90)

In article <6070@accuvax.nwu.edu> randyd@microsoft.UUCP (William R. Day) 
writes:

>In article <5900@accuvax.nwu.edu> uop!quack!mrapple@ucdavis.ucdavis.edu 
>(Nick Sayer) writes:

>>If I'm up late at night, I sometimes hear a short beep from the phone.
>Same here. It seems that every night at about 11:30pm the phones in
>our house give a short half-ring. What is going on? I've decided the
>regularity is too great for this to be random noise on the line.

I get it around 12:30.  For me it's a full ring though.
I have a fax/modem switch on the line, and it things it's getting
a ring and passes it on.  It used to be on my house line and there
it would wake me up, usually every Sunday and Wednesday night.
I've got to assume that it wouldn't normally ring the phone, but that
either my switch is too sensitive, or they are out of spec.  I'd *love*
to know what it is though.


| Alphalpha Software, Inc. | Voice/Fax: 617/646-7703 |   Home: 617/641-3805   |
| 148 Scituate St.         | Smart fax, dial number. |                        |
| Arlington, MA 02174      | Dumb fax, dial number,  |   BBS:  617/641-3722   |
| nazgul@alphalpha.com     | wait for ring, press 3. |   300/1200/2400 baud   |

John Higdon <john@bovine.ati.com> (04/09/90)

In article <5900@accuvax.nwu.edu> uop!quack!mrapple@ucdavis.ucdavis.edu 
(Nick Sayer) writes:
 
>If I'm up late at night, I sometimes hear a short beep from the phone.

In many central offices, there is an automatic testing system that
goes through every idle line in the office and tests for resistance
between conductors (leakage) and resistance to ground. The voltages
used for the test will frequently cause "bell taps" or a short ring in
telephones that do not meet spec for ringer hysterisis and
sensitivity.

I have never experienced that phenomenon here, but then it's possible
my CO doesn't run the tests. Also, I have never had any [Time Magazine]
phones on the line, either.


        John Higdon         |   P. O. Box 7648   |   +1 408 723 1395
    john@bovine.ati.com     | San Jose, CA 95150 |       M o o !

Nickolas Landsberg <npl@mozart.att.com> (04/10/90)

Hi Patrick,

A couple of articles have appeared where people question why sometimes
their phones ring in the middle of the night, apparently on some
scheduled basis.  While I'm not sure that this is THE explanation
for that behavior, it is a possible explanation.

Most switches can be programmed to perform a "line insulation test" on
subscriber lines.  In the days of #1XB and #5XB this involved actually
placing a special circuit on the line which measured the line
resistance, and there was a special "frame" installed in the switch to
do it.  (I had the pleasure of seeing one of these in operation about
10 years ago.  Still used vacuum tubes and a mechanical timer for when
to start the test.)  While I'm not familiar with the internals of how
the digital switches do it, I presume the general concept is the same.
Since measuring the resistance of the line requires placing some
voltage across it (no, I don't know how much), it is conceivable that
this voltage may be enough to trip the ringer on some newer phones.

This test was/is also used to determine patterns of trouble, such as
wet insulation in a cable.  If a number of lines in the same cable all
show low resistance, the chances are the cable has sprung a leak, and
particularly in old cable plant, the paper insulation is breaking
down.  The test is run at night because there is typically low traffic
volume and the testing doesn't have to complete with the dial-tone
provisioning which is first priority and, at least in theory, any
moisture in the cable will "condense" in the evening as the
temperature drops.


Nick Landsberg

Bernie Roehl <broehl@watserv1.waterloo.edu> (04/10/90)

In article <6070@accuvax.nwu.edu> randyd@microsoft.UUCP (William R. Day) 
writes:

>>If I'm up late at night, I sometimes hear a short beep from the phone.
   ...
>Same here. It seems that every night at about 11:30pm the phones in
>our house give a short half-ring. What is going on? I've decided the
>regularity is too great for this to be random noise on the line.

It sounds like a hacker in your city trying to find systems to break
into.  They assume that computers will answer when they see the ring
voltage (i.e. instantly); they run through every phone number in each
of their local exchanges waiting for that instant answer, giving up
right away to avoid humans.

(Odd, though ... I assume you'd still get one complete ring, or none at
all ... maybe it's phone company testing after all...)


	Bernie Roehl, University of Waterloo Electrical Engineering Dept
	Mail: broehl@watserv1.waterloo.edu OR broehl@watserv1.UWaterloo.ca
	BangPath: {allegra,decvax,utzoo,clyde}!watmath!watserv1!broehl
	Voice:  (519) 747-5056 [home]  (519) 885-1211 x 2607 [work]

tn07+@andrew.cmu.edu (Thomas Neudecker) (04/11/90)

>>If I'm up late at night, I sometimes hear a short beep from the phone.
   ...
>Same here. It seems that every night at about 11:30pm the phones in
>our house give a short half-ring. What is going on? I've decided the
>regularity is too great for this to be random noise on the line.

When I ask the 611 repair they said they would call back in a few
minutes.  They and said that I was correct -- they run line tests
between 12-5:00am.  The repair rep said that she could block my
number.  Its only been a few days now and no more early morning rings - 
if the problem returns I will report back.

By the way the chance that it was a hacker power dailing for a carrier
is very remote because such programs require the receiving instrument
to answer and put up a carrier tone.  In my case, and in the others
reported, we receive one short ring.


Tom Neudecker
Carnegie Mellon University