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A Broad Look At British And Australian Phreaking
Anyone interested in amateur radio can go to his local library and find a
shelf of books telling him how to annoy his neighbours by interfering with
their television pictures. Unlike such normal hobbies it is not so easy to
find information on the subject of ?phone phreaking?. When I first became
interested in telephones I was more or less on my own and I spent a lot of
time trying to find other telephone enthusiasts. This was an interesting
exercise, full of odd surprises. On one occasion I spent a lot of time
tracking down rumours of one individual who turned out to be no other than
myself. Some people get interested in telephones simply by meeting
established ?phone phreaks. I feel that one misses something by this.
To understand what ?phone phreaking is all about one needs to know a little
about telephone systems.
The British telephone system telephone exchanges in the UK are arranged in a
hierarchical structure based on about 40 zones switching centres, 350 group
switching centres and about 6,000 minor exchanges. Each group switching
centre (GSC) is a member of a zone and its zone switching centre is its
primary route to the trunk network. Similarly, each of the minor exchanges
has a GSC as its parent. In addition to this basic structure there are
further circuits, GSC to GSC, minor to minor exchange and so on, provided
that there is a sufficient demand to justify them.
Until the introduction of Subscriber Trunk Dialling (STD) in 1959, telephone
operators handled all trunk traffic. By this time most of the network was
automatic in the sense that one originating operator could complete a call
by dialling, over the trunk network, codes which routed the call from one
centre to another.
Following the introduction of STD, the responsibility for the setting up of
the call was placed upon the subscriber.
Now the most costly part of a telephone system is the provision and
maintenance of circuits between exchanges and this dictates the philosophy
behind the working of the system. The STD equipment dials calls over the
trunk network automatically and in this way replaces the local operator. The
equipment is full of safeguards which ensure that, either by accident or
misuse, a subscriber does not waste time on trunk circuits. For example, a
subscriber cannot let a call ring indefinitely: he will be automatically
disconnected after about 3 or 4 minutes.
Most of the automatic switching equipment in the UK is based upon the older
type of electromechanical switching known as the Strowger (or step by step)
system. This type of equipment responds directly to the impulses set up as
one dials. As a result, there is a very close relationship between the codes
dialled and the way in which the call is routed. If one looks at the
dialling code booklet issued to subscribers one will find that it is divided
into two parts. The first gives dialling codes for ?local? calls and the
main part of the booklet gives the dialling codes for ?local? calls and the
main part of the booklet gives the dialling codes for trunk calls.
The local codes operate Strowger switching equipment. If one studies the
local dialling codes published for a few neighbouring exchanges it is
possible to break them down into their component routings. It is then
possible to string them together to reach distances of up to about 70 miles.
It is through discovering this that many people, myself included, first
became interested in telephones. This stringing together of local codes is
known as ?chaining? and is of restricted interest since the lines are
unamplified and of low quality.
The STD codes consist of the digit zero followed by a three digit ?area
code? and, in the case of minor exchanges, further routing digits. The
initial zero connects a subscriber to the STD routing equipment. The next
three digits bear no relation to the routing digits actually needed to set
up the call and are the same all over the country. They were allocated as a
mnemonic in the days when telephone dials had letters on them.
The heart of the STD equipment is a register translator (RT). This splits
off the area code and translates it into the appropriate routing digits,
indeed the same ones that an operator would dial. Meanwhile the remaining
dialled digits are stored in a register. The equipment first pulses out the
routing digits got from the translator and follows them with the digits
stored in the register, these being the final routing digits (for minor
exchanges) and the called number. Having done this the equipment switches
through the speech path and the register translator releases itself in
preparation for the next call, leaving control to a piece of equipment
called a register access relay set. This piece of control equipment has
obtained the appropriate metering rate for the call from the translator, and
when the call is answered it steps the subscriber?s meter at this rate.
Trunk Access
Theoretically, the only way that a subscriber has of obtaining a trunk
circuit is either via the local operator or through the STD equipment.
Neither of these two methods allow one to explore the telephone network,
which is what the ?phone phreak wants to do. In practice there are other
ways of gaining access to the trunk network. For a variety of reasons there
are ways of dialling from the local codes, to which a subscriber has proper
access, onto trunk routes. One way in which this can happen is that
occasionally a local route can terminate at a GSC with the same status as an
incoming trunk route. When this happens one may dial the appropriate local
code followed by the digit ?1? and gain access to the trunk circuits at the
distant GSC.
Another type of trunk access arises when Post Office engineers within an
exchange wire up their own irregular circuits. One of these came to light
last year in Bristol as a result of a Post Office prosecution. One dialled
173 and received a continuous ?number unobtainable? tone (as one should, it
is a spare code). However, if one waited for 30 seconds, this would switch
through to Bristol trunks. One person who was prosecuted was apparently
running an air charter company and making all his telephone calls abroad
free of charge.
A more common type of concealment occurs when, instead of waiting as above,
one has to dial a further code, most commonly a digit zero. If more than one
such digit is required then the access becomes difficult to find.
In spite of such attempts at concealment a large list of these was compiled.
To explore the trunk network using one of these one would use the ?chaining?
method to the nearest exchange providing such a trunk access. If one was
lucky, one?s own exchange would possess one.
As a result of recent publicity the Post Office has tightened up on its own
internal security and now only relatively few of these accesses are left.
Fortunately, there is a more powerful way of gaining access to trunks and
this involves simulating the control signals that are used on trunk routes.
To explain how this can be done it is necessary to describe first the
principles of telephone signalling.
Telephone Signalling Systems
Dial pulses, which originate at the subscriber telephone on dialling,
periodically interrupt the DC path between the telephone and the exchange.
This is known as loop disconnect signalling and is also used over local
links between exchanges. It is not suitable for signalling over longer links
because the pulses get distorted, or over microwave links where there is no
DC path. Over the majority of trunk routes a type of signalling known asAC9
is used. This employs a single signalling frequency of 2280 Hz, which is
within the audio pass band of the circuit. Digits are transmitted as
impulses of this frequency sent at dial pulse speed (10 pulses per second).
Control signals are also at 2280Hz. For example, on completion of a call a
continuous tone at this frequency is sent to clear down the circuit.
The STD system as so far described is inadequate in many ways. It is capable
of providing only relatively simple translations and this is why subscribers
who have STD cannot dial all of the exchanges on the automatic trunk
network. Further, if congestion is met on any of the links within a routing
then the call will fail whereas an operator would either redial or try an
alternative routing. It was decided from the outset that it would be
uneconomical to extend the planned STD system to cope with these problems
and so a different approach known as transit working was planned.
Accordingly, a completely independent trunk network is being built and is
now gradually coming into operation. This is known as the trunk transit
network.
In the transit mode the area code is examined by the originating RT as
before, but instead of producing a complete set of routing digits it simply
seizes the first free circuit to the most likely switching centre capable of
handling that call. If there are no free circuits then it tries its next
choice of switching centre.
This distant switching centre then requests the original area code and upon
receipt of this from the originating RT it will set up the next link in the
same way. The intermediate RT is then released and plays no further part in
the connection of the call. This process continues until the call reaches
its required destination whereupon the distant RT sends back a signal to
initiate the transfer of the contents of the originating register to the
final register and the call is then established as before.
The area code has to be repeated by the originating RT to each of the
intermediate switching centres and a slow signalling system such as AC9 is
unsuitable. A high speed signalling system is therefore used and is known as
SSMF2. This uses a combination of two frequencies out of a total of six to
represent digits. With SSMF2, a digit may be 160 milliseconds, compared to a
maximum of 1 second when using AC9. Signals in the backward direction are
needed, for example to request the area code, and these are based on a
further six frequencies. Supervisory again at 2280Hz in most cases,
including the forward clear for example.
The Blue Box
It has been seen that the control signals employed within the inland trunk
network are audio signals within the passband of the telephone circuit.
Armed therefore with a set of audio oscillators and some means of playing
combinations of these into one?s telephone, one can imitate these signals. A
device of doing this is known as a ?blue box? in the USA and as a ?bleeper?
in this country. With such a device the entire telephone system of the world
is then at your command.
To imitate signalling system AC9 all that one needs is a single oscillator
running at 2280Hz and a method of interrupting this at dial pulse speed. A
second telephone dial is a simple and convenient method. In practice one
would start by dialling an ordinary STD call and then, before the call is
answered, send a short burst of tone. This ?clears down? the call and one is
left with an outgoing trunk route. This first link is not released because
the telephone is still ?off the hook? and the DC holding conditions are
still applied at the local GSC. A second burst of tone will then ?re-seize?
in the sense that the switching equipment is reconnected at the distant GSC
in preparation for the receipt of routing digits. These are sent using the
auxiliary telephone dial just as if one was an operator or was using a trunk
access.
Simulation of the MF2 signals requires, of course, six oscillators and the
procedure is more complicated. However, one does not need to know any
internal trunk routing digits.
Once one has unrestricted access to the trunk network in this way it is
possible to gain access to the international circuits as well. Over these
circuits different signalling systems are employed and these too are
normally ?in-band? systems, in that they use tones with frequencies within
the normal voice band of 300 to 3000 Hz. More sophisticated ?blue boxes?
allow one to simulate these as well and one can go even further and simulate
the signalling used internally in other countries. This is the subject of
Part II of this article.
Having acquired a ?blue box?, the way one explores the network is very much
a question of personal taste and people tend to specialise?as in any hobby.
To start with, most ?blue box? owners just play around and enjoy the novelty
of having the world at their fingertips. Calls to various information
services are popular as are calls to international operators, who are very
friendly. It is a pleasant diversion on a winter evening to discuss surfing
with the Honolulu operator or to chat about the weather with the Sydney
operator.
One type of circuit that is quite popular is the conference call whereby a
number of enthusiasts are connected together: here the conversation often
tends towards ?phone phreaking. This type of circuit arises either by
accident or by design. One example of the ?accidental conference? was Derry.
One of its dependent exchanges got demolished by a bomb and all circuits
from Derry to this exchange were connected together onto a recorded
announcement. This recorded announcement became disconnected and a
conference was born. Conferences also occur on an international scale and
are very popular in America, where they are sometimes very sophisticated.
So far nothing has been said about the legality (or otherwise) of ?phone
phreaking. Using a blue box one can make a ?phone call to virtually anywhere
in the world at the cost of a local call or even free of charge. To make a
?phone call to somebody in this way is clearly fraudulent and if caught you
would face prosecution. On the other hand, to use a ?blue box? for the
purpose of exploring or studying the telephone system the situation is by no
means so clear. When using an AC9 simulator, the very first forward clear
causes the equipment to start metering the call and it does so, at the rate
appropriate to the initial STD call, for as long as the telephone is off the
hook. This occurs because the equipment mistakes the forward clear for an
answer signal. For this reason the initial STD call is chosen to give a low
metering rate. If one now restricts one?s activities to such areas as, for
example, experimenting with different signalling systems then the law is
very unclear on the subject. There is certainly a good argument against
one?s activities being illegal.
It is so easy to make STD or international calls free of charge, even with
no electronic aids, that anyone wishing to do so would certainly not use a
?blue box?. In this country at least, the ?blue box? user is generally a
telephone enthusiast and fairly harmless.
The world is but a Blue Box away
This part of the article describes the extension of the art of phone
phreaking from a national to an international scale. As already mentioned,
once one has unrestricted access to trunk routes then one may also gain
access to international routes. The way in which one can achieve this varies
between countries.
In large countries possessing an advanced telephone system such as Australia
or the USA, there are centres from which operators can originate
international calls. Today, most of the world?s telephone network is
automatic?which means that these originating operators can complete their
international calls without the assistance of an operator in the distant
country. The automatic switching equipment giving access to international
circuits is located at centres known as Gateway exchanges, and
operator-originated international traffic is first of all routed over a
country?s internal network to these gateway exchanges. Since the internal
network therefore, carries both national and international traffic, it is
easy to see that with the unrestricted access to this network provided by a
Blue Box, the telephone enthusiast can himself route calls via Gateway
exchanges (provided of course, that he knows the appropriate routing codes).
In this country, however, the situation is different. Until quite recently
the only international operators were those located at the gateway exchange
itself? that is, at London?s Faraday House?and subscribers were connected to
these operators by the local operator in their own exchange or Group
Switching Centre. There were no ?shared traffic? routes terminating at the
automatic equipment in the Gateway exchange, as in the USA. It was therefore
impossible for the telephone enthusiast to gain access to international
routes until 1963, when subscribers were themselves allowed to dial
international calls. And as a result, such access requires a knowledge of
the workings of International Subscriber Dialling.
International Subscriber Dialling
International Subscriber Dialling (ISD) is the logical extension of STD. It
enables subscribers to dial their own international calls and was first
introduced in this country in 1963, between London and Paris. Other areas of
Europe soon become available and later still, North America. The service was
also made available to other areas within the UK.
One major problem associated with the introduction of ISD was not a
technical one but concerned the agreements that had to be made between
different countries regarding the charging of calls.
ISD works as follows. By international agreements, every country is
allocated a ?country code? (CC), examples being France (33), the UK (44),
Israel (972) and the USA (1). In the UK a standard area code (10) is
allocated to ISD and the call is handled by the register-translators (RTs)
at the subscriber?s local exchange, in much the same way as for an ordinary
STD call, the subscriber dialling an initial digit 0 to gain access to this
equipment. The complete ISD dialling code is then the prefix 010 followed by
the country code and then the area code within the distant country.
Upon receipt of the ISD prefix, the originating RT examines the country code
to check its validity and to determine the appropriate metering rate. For a
valid country code, the call is then routed over the GSC trunk exchange onto
direct circuits to the automatic equipment at the London International
Exchange, the originating RT being then released.
Until recently, one could dial, either over a trunk access or by AC9
simulation, the appropriate routing code, which gives GSCs access to the
International exchange. By by-passing the RTs in this way, the equipment did
not ?screen? the country code that you sent and so you could enjoy full
international operator status. One example of this was Edinburgh, where the
trunk routing code 515 gave you the International RTs in London. Such direct
methods are no longer available owing to considerable misuse, apparently by
Post Office employees.
It is not obvious, by the way, why one would route the call via Edinburgh
instead of going directly to London. The reason is that London is
sufficiently large to justify the provision of special trunk exchanges to
handle STD and ISD calls exclusively and the only routes onto these is via
originating RTs at the local director exchanges: there is no way to bypass
these or even gain access to them incoming into London.
It was Post Office policy to introduce ISD at provincial non-director areas
only over the trunk transit network, so that it was not until early 1973
that the first of these (Cardiff) had ISD. Other exchanges soon followed but
for the sake of illustration we shall consider Cardiff.
In September 1 972 the first circuits between Cardiff and the London
International Exchange appeared. By dialling Cardiff trunks and then the
code 12 one received a signal intended to initialise the transfer of digits,
in SSMF2 form, from the Cardiff RT to the international registers. If one?s
Blue Box was capable of sending SSMF2 one could respond to this signal, send
whatever country code one pleased into the international registers, and
again achieve international operator status. Those lucky enough to possess
an SSMF2 Blue Box enjoyed the novelty of this new route to the rest of the
world.
The Post Office was disconcerted at this traffic appearing as soon as the
circuits were installed and very quickly (i.e. a year later) took steps to
prevent such misuse. By the following February the Cardiff RTs had been
programmed to accept SD calls and the service became available to the
public. (Coin boxes in Cardiff, incidentally, could not handle the high
metering rate on calls to North America and so these were free of charge).
TELEPHONE SYSTEMS IN OTHER COUNTRIES
Once a call has been set up to another country it is possible to simulate
the signalling employed over the international route and to explore the
internal network of the distant country. The two most important signalling
systems used over international circuits are known as CCITT4 and CCITT5.
In the signalling system CCITT4 digits are sent as four-bit binary numbers
using two frequencies, 2400Hz and 2040Hz, to represent 0 and 1 respectively.
The control signals also use these frequencies. Digits are sent in response
to signals received from the distant equipment, and the transit method of
working is generally employed between different countries. (The principles
of the transit working have been described in the first part of this
article, as they apply to the internal trunk network in the UK).
This signalling system is unsuitable for use over satellite circuits since
these introduce a return signal path of about 100,000 miles in
length?corresponding to a time delay of some 600 milliseconds. In a
compelled signalling system such as CCITT4 this delay is added to the
sending time of each digit which makes the overall setting-up time for a
call for too high, bearing in mind the need for efficient use of expensive
satellite circuits. CCITT4 finds its main application over shorter
international routes, the main areas being Europe, South America and Africa.
Over intercontinental and satellite circuits the system CCITT5 is normally
used. This is a high speed signalling system. Digits are sent in
multifrequency (MF) form similar to the SSMF2 system already described but
using different frequencies. The CCITT5 frequencies are the same as those
used by the American Telephone and Telegraph Company (AT&T) for the North
American internal signalling system, which is very convenient for the Blue
Box user. The two signalling systems differ only in the supervisory or
control signals.
The simulation of CCITT4 was of great interest to the telephone enthusiast
in the early days of ISD when the international RTs handing ISD traffic had
access only to those countries to which ISD was allowed. For example, Russia
was first reached in this way; a call to Switzerland (which was allowed) was
made and then extended to Moscow via the Warsaw transit.
Since then, the equipment known as International Common Access (ICA) over
which international operators connect calls, has become available for ISD
traffic and most countries are now directly available to the enthusiast by
the methods described above. With the availability of ICA interest in CCITT4
simulation has diminished.
Simulation of CCITT5 is simpler than for CCITT4 since one does not have to
respond to backward signals and the procedure is simpler. Furthermore, with
the addition of a single frequency, 2600Hz, the simulator can be used within
North America. If one is actually in North America then the procedure is
indeed very simple and it requires very little effort to make calls free of
charge to almost anywhere in the world. This accounts for the tremendous
popularity of Blue Box in that continent, the vast majority being primarily
interested in saving money on telephone bills. There are only a handful of
enthusiasts interested in telephones their own sake.
It is possible to simulate the North American signalling system from the UK.
The procedure is best described means of an example. Suppose you felt
inclined to telephone an adjacent ?phone box via America you would proceed
follows. First set up a call to, say, the Philadelphia weather forecast.
Having done this you would send a short burst of 2600Hz. This is a ?tone on
idle? supervisory frequency?that is, the application of this tone will
?clear down? the US internal circuit and its removal will reseize a circuit,
the international circuit from the UK to the USA be unaffected. Next you
would send (in MF form) the following digits?KP 212-183 ST. The signals KP
(Key Pulse) and ST (Start) are MF signals, which must enclose blocks of
digits sent. This will connect you to area 212 (New York) and to the
?overseas sender? in that Gateway, the code 183 being its international
access code. When this equipment is ready to receive digits it returns a
continuous tone whereupon you send KP0441 838 7062 ST. The initial zero is a
dummy digit, 44 is the country code for the UK, 1 is the area code for
London and this is followed, in this example, by the required London number.
I find the Australian telephone system much more interesting than American.
There are two independent trunk networks Down Under?the (multifrequency
compelled), and the 2VF (two voice frequency), handling STD and
operator-originated traffic respectively.
As far as I know, nobody outside of Australia has managed to simulate the
MFC signalling, the difficulty being that the control signals are ?outband?
(sent outside the normal 3000Hz voice frequency band). But provided that one
is incoming into Australia with operator status one can gain access to the
2VF network at centres such as Melbourne or Brisbane. This assumes that one
knows the appropriate access codes. The 2VF network employs the AC1
signalling system, which uses two signalling frequencies: 600Hz and 750Hz.
Digits are sent in a similar to AC9 signals but use the 600Hz frequency. The
supervisory signals are different, the forward clear for example,
consistency of the 750Hz tone applied for 2 seconds followed by 0.7 seconds
of the 600Hz tone. This signalling system preceded AC9 in this country and
is still used to some extent. One can sometimes hear its very characteristic
?forward clear? tone over UK trunk routes when crosstalk occurs between
channels using AC1.
Australia has one Gateway exchange, located in Sydney, and a second coming
into operation shortly. Modern Crossbar switching is employed at the
Gateway, and this has the facility of restricting the access to the outgoing
circuits in the transit mode to the appropriate incoming routes. This means,
for instance, that if you were incoming from London, the country code 44 for
the UK would not be accepted, because the equipment can recognise that calls
from one part of the UK to another are not normally routed via Sydney, even
though a telephone enthusiast might consider it a reasonable thing to do. In
practice, transit access from Sydney to New Zealand, Hong Kong and Malaga is
all that is allowed to UK traffic?which is of restricted interest to the UK
telephone enthusiast since these countries are available directly via the
International Common Access System.
>From the enthusiast?s point of view it is therefore fortunate that there is
a way of gaining unrestricted access to the international exchange and this
works as follows. Operators in certain large exchanges, such as Adelaide,
can dial their own international calls, rather than having to rely upon the
international operators in Sydney. This traffic is routed over the 2VF
network and, as has been mentioned above, it is possible to gain access to
this network incoming into Australia. This makes it possible to set up a
telephone call all the way round the world.
Firstly, set-up a call to Adelaide via New York (or some other US Gateway)
and then send the 2VF access code and the 2VF routing for Sydney, all using
CCITT5/USA signalling. Having allowed this connection to complete, the
distant 2VF circuit will now accept AC1 signals. Using the pulsed 600 Hz
signalling for the digits, one next sends the digits 99 1 44 2 1 838 7603
followed by a short burst of tone at 750Hz to indicate end of signalling.
The digits 99 are the access code for the Gateway exchange, the digit 1 is
used for discrimination purposes and the country code 44 is for the UK. The
next digit, 2, is known as a language digit and indicates in this case that
the call is being set up by an English speaking operator. The area code for
London is 1 and this is followed by the required London number. This rather
cumbersome procedure follows from difficulty in interfacing an older type of
signalling, AC1, with the international routing equipment. A call set up in
this way will be routed, via the Indian ocean satellite, back to London.
This feat was first achieved in the June of 1972.
The term ?language digit? referred to above is rather a misnomer and
originated in the days when most of the international circuits were operated
manually. This meant that an originating international operator could not in
general complete a call but would require the assistance of an operator in
the distant country and the purpose of the language digit was to ensure that
the call was routed to an assistance operator speaking a specified language.
Today, the bulk of international traffic is switched automatically and
furthermore the English language has become more or less universally used by
international operators. A few countries such as France and Russia insist on
using the French language. Spanish is used to some extent within South
America but in the vast majority of cases the language digit has become
redundant. Its use is however mandatory by international agreements and must
be used.
Many countries now have ISD and with the increase in subscriber originated
traffic international agreements have come into force that require such
traffic to carry the language digit zero. This is to allow discrimination by
the incoming equipment to prevent certain types of call. For example, a
subscriber is not allowed access to an assistance operator. When ISD was
first introduced to New York from London one could dial New York using the
published dialling code 0101 212, followed by the New York number. But
instead of dialling a New York number, one could dial a further North
American area code and follow this by 1211 to reach the incoming assistance
operator in that area, free of charge. This gave interesting possibilities,
you could call the Montreal operator and ask for Sydney, then ask Sydney for
Hong Kong. All of this is possible to a Blue Box user but in those days it
was quite novel, and required no special equipment or dialling codes.
Today, discrimination by means of the language digit ?0? prevents all this.
This language digit is automatically inserted by the London ICA equipment
when accessed via ISD routes and it follows, therefore, that traffic to, say
Australia (a non-ISD country) having this language digit can only have
originated from a telephone enthusiast. In an attempt to thwart such
activities the Australian authorities have arranged for the incoming
equipment to reject incoming traffic from London with this language digit.
This can only be a temporary measure since ISD to Australia will be
introduced in two or three years time. In the meantime, one can route calls
via the USA or, say, Copenhagen, using methods described above. Throughout
the world the various telephone administrations are making increasing
efforts to prevent the activities of the telephone enthusiast and it is
this, I think, that will keep the hobby alive as new areas of exploration
diminish. After all it?s nice to beat the system but even nicer to beat the
people trying to stop you.
By DUO_PROS (aka Happy McSmith)