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From: howard@cos.UUCP (Howard C. Berkowitz)
Newsgroups: comp.dcom.telecom
Subject: Re: Submission for mod.telecom (Modems and data jacks)
Message-ID: <207@cos.COM>
Date: Wed, 22-Apr-87 14:00:07 EST
Article-I.D.: cos.207
Posted: Wed Apr 22 14:00:07 1987
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I do want to emphasize that it's bad practice to transmit at a higher
level than that which is designed for a local loop; it's quite accurate
that louder is not always better -- but it is important to be loud enough.

The worst horror story I've heard on excessive level, which may be
apocryphal:

An [unnamed by my informant in DATEC] user called his telephone test
board for a problem with the remote site's Bell 829 data auxiliary set.
[This is an interface device, for Telco use, which has a tone-operated
loopback feature].  The user complained that the unit would not go
into loopback.

Now, 829's are for telco use, not customer.  Most telcos are happy,
however, to let customers use them for fault isolation.  The 829
is put into loopback with at least a 1-second application of
2713 Hz tone.

In the story, the helpful test board tried to loop back the 829
in question.  It worked perfectly, but the user couldn't get
it to loop.  The test board then asked the customer to describe
exactly what he was doing; the answer was "oh, I send out 2600 Hz
at a good hot +10-20 dBm -- the limiter drops it to a legal level."

Horrified silence from test board.  A mystery of the last week
just resolved.

Over the past week or so, the telco had been installing a new
electronic switch in its central office, a switch equipped with
toll fraud detection.  "Blue Box" fraud uses a 2600 Hz tone;
somehow, the user assumed this was the loopback frequency.

Because the user 2600 tone went out at an extremely high level,
it crosstalked a large number of pairs in its cable.  The
new switch kept reporting massive simultaneous toll fraud attempts
(i.e., pure 2600 on a subscriber loop), a sufficiently large number
that equipment failure was assumed.  The switch had been torn
down repeatedly to find out why it assumed massive toll fraud
was in process.