nasty

话带数据中传真解调程序

From discuss-return-332-pavel=[e-mail]  Tue Sep 14 11:57:20 1999
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Date: Tue, 14 Sep 1999 11:56:42 +0200
From: Pavel Machek <[e-mail]>
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Subject: Damaging telephone network
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Hi!

After discussions if non-homologed modem can cause damage to telephone
network, I decided to write file "telephone damage howto".

> Telecomms regulations are taken very seriously in many countries,
> because it's so important.  It's only recently that the network got
> really robust, and I think only in the better developed countries.

We certainly have some pretty old phone switches here, and they are
undamageable, too. It is simple: lightning likes to hit phone
lines. Phone switches need to survive that.

You can do few nasty things to telephone network:

1) Pick up 1000 phones at once on one telephone switch. You can
overload its power supply this way and it may explode. On newer phone
switches, software likes to crash due to overload. It doesn't make any
permanent damage but the switch obviously crashes and then
automatically recovers, which MAY render it out of service for a
couple of seconds/minutes.

2) Inject unallowed frequencies. These frequencies are not used except
for the 16kHz, which is used for transferring meter pulses to remote
(subscriber's) private meter. However, it cannot be abused for making
free calls - the switch can only transmit these frequencies, not
receive it - so it is useless to send them to it. Czech PSTN network
was never fraudable by using tones - the only exception was to make an
intrusion to the communication of other party using the 2700 Hz
frequency, generated for example by the dog's whistle.

3) Dial numbers such as 13A (A is 11 pulses, for pulse dialing,
special tones in DTMF.). Many interesting numbers may be found there,
like all the recorded messages, special test trunks and other
features.  SOMETIMES one may find a toll-free route to some
interesting destination (like international gateway) but SPT people
are much more careful than on the beginning and such numbers are VERY
rare now.

4) Put a pemanent voltage (like 230V/50Hz) to the telephone
line. There were cases that the switch totally burned out (only the
metallic parts remained) by connecting a fax with a broken power
supply which put the mains live wire directly to the line. The reason
is very simple: the lightning protectors of some older types open on
such a voltage and flowing current causes their overheating. They may
then serve as a fire initiator.

5) On an electromechanical switch (P51), connect some atypical
resistance to the line. The loop relay then doesn't close fully and
may switch some circuits to the unstable state with high power
consumption. However, the fuse obviously is the only element which is
destroyed by this.

6) On an electromechanical switch (P51), use VERY distorted dialing
pulses. You may block the mechanism of the step-by-step selector. The
fuse will blow and the selector will need to be repaired manually.

								Pavel
PS: If you have some corrections, additions, etc, let me know. From
above list, I think it is obvious telephone network is not easily
damaged. Lucent modems certainly are not capable of putting 230V/50Hz
onto line. P51 switches are being slowly replaced even in our country,
I do not think you can find them in developed world.

-- 
The best software in life is free (not shareware)!		Pavel
GCM d? s-: !g p?:+ au- a--@ w+ v- C++@ UL+++ L++ N++ E++ W--- M- Y- R+