Note: Descriptions are shown in the official language in which they were submitted.
1638~1639/~/90 -1-
TEIEPHQNE LD~E MQNlTQRlNG~ APPAR Aq~US AND ME~2
Field of the In~Tention
The present invention relates to fax monitoring apparatus. More
particularly, the invention relates to a monitoring apparatus which is
capable of monitoring fax transmissions which take place between two
fax transmitting apparatus connected through a telephone line.
In another aspect, the invention relates to the monitoring of telephone
lines, and more particularly to a method by means o f which it is possible
to identify the type of act*ity associated with a telephone line which is
being monitored, and to record such activity.
Baçk~round of ~e ln~entiQn
Fax transmissions have become more and more popular, and the
volume of information transmitted through fax machines is increasing
steadily. This has caused a number of problems, for instance, in that
unauthorized transmission of material may occur from a given location,
without leaving any trace, or fax machines may be used for criminal
activities to bypass police wiretapping of normal telephone lines.
The present invention has as an object -to pro~ide a fax monitoring
machine which may monitor, record, store and retrieve -fax
transmissions which intervene between any two ~ax machines. Thus, it
is one object of the present invention to provide a machine which may be
located between any two fax machines which are communicating, may
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1638tl6391EI/90
receive information transmitted from both fax machines during
communication, and may permit to follow a transmission and analyze
the material transmitted.
If the apparatus of the invention is used in open analysis of
transmission, e.g., in an industrial location, it is not overly important to
make sure that the transmitting and receiving fax machines do not
detect that the transmission is being followed (however, it is of course
necessary to avoid disturbances of the line which may cause a
malfunction of the machines). On the other hand, in many other
applications, such as for police wiretapping, it is important that the
transactions of transmitting and receiving fax machines be monitored
and recorded by the monitoring apparatus without making it evident
that wiretapping exists. In all cases, it is desirable to avoid any
interference with the two communicating machines. It is therefore
necessary to provide an interface which is transparent" to the
handshake, and which does not leave any record of its presence, either
on the transmitting or the receiving machine, ;md which cannot be
easily discovered by line-analyzing apparatus. Such a monitoring
apparatus interface must be activated by the activity taking place on the
telephone line between the two monitored machines, must record the
transmission intervening bet,ween the two machines, but must not
interfere with the transmitted signals or transmit any signal which
act*ely takes part in the handshake between the apparatuses.
Providing such an interface is one of the purposes of this invention. It
should be noted, however, that such a transparent interface will not
prevent the operator from voluntarily interfering with the transmission,
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1638/1639/l~V90
e.g., to stop the transmission of a non-authorized message, iP
appropriate interference means are provided. r
Thus, it is another object of the invention to provide a fax monitoringapparatus which can effectively monitor transmission of fax messages
occurling between two fax apparatuses, without leaving any trace of its
presence, either on the transmitting or the receiving apparatus, and
without being easily detectable by wiretapping-detecting apparatus.
It is well known in the art to connect two telephone lines, for instance for
policing purposes, and to eavesdrop on telephone conversations.
However, when monitoring a plurality of lines at the same time, it is
necessary to provide means for the automatic identification of activity
starting and ending, and for the recording of telephone activity in an
automatic manner, since a single operator is not capable of following a
large number of telephone lines. In the art there are known devices
which can be connected to telephone monitoring and recording
apparatus for this purpose, which identify the starting and ending
activity of a given telephone line by following the changes in voltage of
the line. As it will be understood by a skilled person, using the telephone
line, e.g., by lifting the receiver, results in changes of voltage which
drops, when the line is used, from its previous value to a lower value.
The problem with this type of monitoring is that different telephone lines
show different voltages, depending on the type of line, area, position of
connection to the telephone line, and so on. Therefore, although
nominal voltages of about 48V should exist on normal telephone lines, in
many instances the actual value is much lower, and sometimes even
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1638/1639/EI/90
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higher. Furthermore, the amount of voltage drop, after the receiver is
lifted, is highly dependent on the distance between the receiver and the
exchange central. For this reason devices known in the art are provided
with adjusting means, normally a potentiometer, for adjusting the
reference voltage before initiating monitoring of a telephone line~
These devices known in the art suf~er from several considerable
disadvantages. First of all, it is necessary to adjust the reference voltage
for each monitored telephone line every time the device is allocated to a
different monitored line. This is laborious and time-consuming.
Furthermore, even when the same telephone line is monitored,
fluctuations in the actual voltage of the line exist, so that the actual
value may be different from the reference value which has been set by
the operator, which results in faulty fùnctioning of the system, missing
required activations of the recording apparatus, etc.
It is therefore another object of the present invention to provide a method
which overcomes the aforesaid disadvantages, and which can be used
for accurately monitoring the activity of a telephone line, withaut the
need for manual settings of reference values.
It is still a further object of the invention to provide an apparatus which
can be used for the aforesaid purposes.
It should be no-ted that by "telephone line" it is intended to include all
lines which are adapted to be used for transmitting telephone
conversations, including lines which are dedicated to telecopying
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163~3/163~/lEI/90 r
apparatus or computer transmission or the like. Thus, -the outcome of
the monitoring of a given telephone line could be a recording oE a fax
transmission or a voice conversation, or any other type of data
trans.mission, and the actual nature of the transmitted conversation is
not important for the purposes of this invention.
The fax monitoring apparatus according to the invention co~nprises:
- One or more line interface means to simultaneously detect and analyzeall audio signals produced on any given telephone line by two connected
fax machines;
- Analysis means to analyze and interpret the said audio signals to form
a compressed fax image;
- Expansion means to extend the compressed fax image into a bit-
mapped image;
:
- Storage means, to store the compressed fax image an~Jor the bit-
mapped image;
- Display means to display the bit-mapped image of the original fa~
transmission; and
- Optionally, printing means to provide a hard copy of the transmissionor part thereof.
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~638~1639/~I191) -6-
According to one embodiment of the inventiorl, the storage means
comprise a temporary memory or bu~fer, and one or more hard disks.
Furthermore, in another embodiment of the invention, the storage
means further comprise one or more digital cartridge recorders and,
optionally, one or more floppy diskette drive and/o:r optical disk drive. Of
course, any other mass storage media can be employed, as becomes
available from time to time.
According to a preferred embodiment of the invention, the line interface
means comprise a non-interfering line interface device comprising a
circuit consisting of two symmetrical main branches connected to an
isolation amplifier, two or more protectors being connected parallel to
the isolation amplifier, the said two protectors being connected to the
ground and the total impedance of each branch before the connection to
the protector line being substantially smaller than the impedance of the
branch after the said con~ection. Preferably the ratio of the ~maller to
the greater impedance of each branch is about 1:5.
According to another preferred embodiment of the in~ention a separate
modem is provided for each monitored telephone line. This is different
from other existing apparatus in which it is attempted to exploit a single
modem for several telephone lines. It has been found that using the
same modem for a number of lines is not convenient, because one
modem can $ake care OI a single telephone line at a time, and when two
different telephone lines are operating at the same time, and fax
transmissions are transmitted thereon, one single modem cannot
handle both.
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1638/1639/EI190 7
The apparatus according to the present invention can further be used tomonitor and record mixed voice/fax transmissions. Additionally, the
apparatus can be exploited for monitoring and recording telephone
transactions which are entirely voice transactions. This, as will be
apparent to a person skilled in the art, is very important because in
many instances fax transmissions are preceded or followed by voice
conversations, or a telephone line which is in principle dedicated to ~ax
transmissions can be used for voice conversations. According to one
embodiment of the invention, this is achieved by adding an analogue-to-
digital transducer connected in parallel to each modem, to transform
audio signal transmitted through the telephone line into digital storable
information.
The apparatus can be activated by any suitable method which permits to
recognize the activity of the telephone line. One such method which is
novel and forms a part of the present invention comprises:
- continuously sampling the voltage of the telephone line to be
monitored;
- calculating the mean value of the voltage from a plurality of
samplings taken during a given time interval;
- comparing the said mean value of the voltage with a reference
voltage defimed as the mean voltage obtained during the previous
time interval;
- replacing the value of the re~erence voltage with the said mean
value;
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:1638/1639/H190
- if the di:~rence between the last calculated :mean value and -the
re-~erence value exceeds a predetermined value:
(a) stopping the replacement of the ref`erence voltage with
the mean calculated value of the voltage;
~ b) activating signal recording means to record signals
transmitted through the telephone line;
(c) continuously comparing the calculated mean value with
the reference value, and if the diff!erence between the two
compared values is below a predetermined minimal value:
1) deactivating the signal recording means; and
2) resuming the replacement OI the value of the reference
voltage with the calculated mean value of the voltage, and
the subsequent steps.
The signal recording means referred to above can be, in this case, an
apparatus according to the invention.
According to a preferred embodiment of the invention, the method
further comprises recording and analyzing the telephone number
which is dialed by a monitored telephone line, which method includes
the steps o
~ 1) identifying dialing beginning by comparing the calculated mean
value of the voltage and the reference voltage, and determin;ng whether
the difference is below a predetermined ma~imal value;
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16381163~/EI/90
(2) counting the number of pulses of high voltage occurring within
about 01 second from one another ti a predetermined tolerance), to
determine the dialed digit;
t3) identify~ng the end of one dialed digit by identifying a low-voltage
interval of a length exceeding about 0.1 second ~-~ a predetermined
tolerance);
(4) recording the said pulses of high voltage or the equivalent digits of
the dialed number in the signal recording means.
As in many instances mixed dialing, including pulse and tone signals,
is employed, e.g., to activate a telephonic secretary, a preferred
embodiment of the invention further comprises providing tone-detecting
means to identify and record tone-modulated codes and/or digits.
While the maximal difference between the calculated mean value of the
voltage and the reference value can be changed, on the basis of various
considerations which are within the scope of the person skilled in the
art, it is preferred to initiate recording of telephone line activity when the
calculated mean value is equal to or less than 80 - 85% of the reference
voltage.
The mean calculated voltage is obtained, as said above, by averaging a
large number of samplings taken during a very short period of time. In
a preferred embodiment of the invention, the mean calculated voltage is
the arithmetic mean of 200 to 6,000 samplings, preferably about 1,000
samplings taken during a time interval of about 1 second.
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1638~1639~I/90
-10-
The activity of a telephone line may be recorded on a variety of recording
media. In a preferred embodiment of the invention the recording means
comprise digital record;ng apparatus, and the activity of the telephone
line is saved in the form of a digital record.
The invention filx ther encompasses a device ~or monitoring and
analyzing the activity of a telephone line, which device comprises:
- sampling means for continuously sampling the voltage o~ the
telephone line;
- calculating and comparing means for calculating and comparing
mean values of the line voltage. These calculating and comparing
means may be, e.g., a microcomputer or a microp-rocessol~;
- activating means for activating signal recording means. These
activating means may, again, comprise a microprocessor or a
microcomputer; and
- signal recording means to record the activity of the telephone line.
Encompassed by the present invention is also a method of monitoring
~ax communication, which method comprises the steps of:
a) providing line interface means connected to a telephone line to be
monitored;
b) providing activating rneans to detect line activity comprising one o~
start/stop act*ity, ringing and dialing pulse and DTMF signalling;
c) providing interpreting means activated by the said activating
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~638116~9/EI/90
means;
d) interpreting fax transmissions by means of the interpreting
means when line activity is detected;
e) assembling the interpreted fax transmission into compressed fax
images;
f) storing the compressed fax images in memory means;
g) retrieving the stored compressed fax images and expanding them
to bit-mapped images of the original message; and
h) displaying the bit-mapped images on display means, or prin-ting
them out on printing means.
In a preferred embodiment of the invention, the display means comprise
a graphic screen, whereby information can be displayed on the screen.
The screen can also be exploited to look for information to be printed on
the printer.
In order to further illustrate the invention, Figs. 1 to 7 are provided, in
which:
- Fig. 1 is a block diagram of the information flow in a device according
to an embodiment of the in~ention;
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16381~639/~V90
-12-
- Fig. 2 is a schematic view of an apparatus according to one
embodiment of the invention;
- Fig. 3 is a schematic representation of part of the receiving part of an
apparatus according to one embodiment of the invention;
- Fig. 4 is a diagram showing a line interface according to the
invention;
- Figs. 5 and 6 each show an alternative system set-up, in block
diagram; and
- Fig. 7 shows the aotivity of a telephone line frorn which a number isbeing dialed.
In Fig. 1, it is seen that the incoming lines are fed to the line interface to
be described with reference to Fig. 4. Under this protection the signals
are fed through decoding means, which decode the modem signals or
translate voice modulation into digital data and transfer the signals to
memory means in the apparatus. These memory means are the
temporary memory means, from which the information is transferred
to storage media such as hard disks and tape recordersO When it is
desired to view the information and analy~e it, th~ fax information is
retrieved from the hard disk or the tape, is expanded and is sent to view
means, e.g., a screen or a printer. Similarly, voice information can be
retrieved for and sent to appropriate voice regeneration apparatus.
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116391H/90
-13-
Turn;ng now to Fig. 2, an apparatus according to one embodiment of! theinvention is indicated by numeral 1. This apparatus comprises
interface means (not shown), floppy disk drive 2, two digital casette
recorders 3 and 3', and two hard disks, 4 and ~ casette compartment
~, is also shown, which of course is not essential. The apparatus is
provided with two screens, a graphic screen 6, on which fax images are
displayed, and a messages screen 7, which is used by the operator for
messages, for instance for working with the memory means, to retrieve
specific fax messages by their stored names, and for other control
activities. An additional floppy disk drive 8 is provided, which is used to
start up the program which controls the operation of the device. The
operation of the apparatus is controlled through a keyboard 9, which is
used to input commands for the various operations of the apparatus.
Thus, when a fax message is detected and is sent by the line interface
means to the decoding means, after having been decoded it is stored in
the hard disks 4 and 4', and in the digital casette recorders, 3 and 3'.
Normally, storage from the temporary memory buffer is done in the
hard disks, and later the information is transferred to the digital
casette. However, it is possible to indicate which kind of informakion is
to be maintained on the hard disk for an early review, and which is to be
sent to the digital casette for long-term storage.
When the operator wishes to view a specific fax message, he gives the
appropriate commands through the keyboard 9 and the~message
appears on the graphic screen 6. Alternatively, or additionally, the
message may be automatically printed out by a line printer, not shown
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1638~1639/~I/90
in the figure for the sake of simplicity. The line printer should
preferably be a laser printer or another comparably high-speed and
heavy duty device.
The operator will identify different messages through the messages
screen, e.g., by telephone numbers, time of transmission, or any other
indication. Thus, for instance~ ;f the operator sees on the message
screen 7 that a given ~a~ apparatus is transmitting, he will also see on
the messages screen how and where the fax transmission is be;ng
stored, will be able to retrieve the fax transmission, view it on the
gr~phic screen 6, and if desirable, will be able to print it out on a printer.
As will be readily understood by the skilled person, the mode of operation
described above is unique inasmuch as it permits to monitor a very large
number of telephone lines, to store fax messages transmitted
therethrough on long-term storage media, to review the messages at
will, and to provide hard copies of these messages. This is achieved by
the unique combination of elements and the method of operation of the
apparatus of the invention. Of course, the invention can conveniently be
exploited also when a single line is monitored.
...i`
In Fig. 3 the receiving part of the apparatus of Fig. 2 is schematically
shown, which comprises a plurality of modems 11, each of the said
modems being connected to a telephone line 12, only two such modems
and telephone lines being shown, for the sake of simplicity. Parallel to
each modem there is connected an analogue-to-digital transducer 13,
which has the purpose of translating ~oice messages into digital data.
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~638/16391EI190
-15-
Memory means 14 are provicled, for intermediate storage of data
received from modem 11 or A-to D transducer 13, which can be divided
in a plurality of sub-units, or which can consist of separate and
connected memory units. The intermediately stored information from
intermediate memory means 14 subsequently flows to central or main
elaborating means 1~, not described in detail here and which have been
described with reference to Figs. 1 and 2.
As will be apparent to a person skilled in the art, the modem 11 is only
capable of recognizing fa~ transmissions and there~ore it will be
activated only when the information transmitted on the telephone line is
a fax transmission. If speech is transmitted on the telephone line, then
the A/D transducer 13 will be activated, and modem 11 will not be
operative. Information will flow from the telephone line to intermediate
memory means 14 via the A/D transducer 13.
Referring now to l?ig. 4, the line inter~ace device shown in the figure is
connected to telephone line 12 through connections 12a and 12b. The
circuit which constitutes the line interface has two identical branches
generally indicated by 16 and 16', which are connected to the bases of an
isolation amplifier 17. Connected and parallel to the isolation amplifier
17 there is a protecting branch 18, on which there are located two
protectors 19, between which there is found the connectioT~ to the
ground. An additional impedance, indicated by numera~ 20, is also
found in parallel to the isolation amplifier. As will be seen from the
figure, the total impedance of the part of branch 16 which is found
between cormection 12a and protecting branch :18 is much smaller than
1~;3811639~I/90
-16-
the remaining impedance of the same branch, being 1 MQ, the
remaining impedance being, in this particular embodiment of the
invention, 4.7 MS2. It should be understood that the dimensions of the
impedances in this circuit are dictated by the various requirements of
the circuit. On the one hand, it is necessary to provide -the highest
possible impedance, to render the interface as much non-detectable as
possible. On the other hand, the protectors 19, together with the
res;stance found before them7 will constitute a filter to the signal coming
from the telephone line, because the protectors include a capacitance.
Thus, it is necessary to di~ride the resistance along the branch of the
circuit to maintain a high level of non-detectability, while avoiding too
high a ~ltering effect of the various components. One suitable isolation
amplifier is, e.g., the AD202 ampli~ler, manufactured by Analog
Devices, Inc.
The reduction of the signal from the telephone line resulting from the
arrangement of the circuits shown in Fig. 4 is about 50:1. This enables
khe line voltage analyzing circuitry to deal with low level signals.
However, since the audio signals are also attenuated by the same ratio it
is necessary to amplify further the audio signal after the isolation
amplifier. According to one embodiment of the invention, an additional
amplifier, which need not be an isolation ampli~er, is provided a~ter the
isolation amplifier 17, as indicated in broken lines by numeral 21 in Fig.
4.
An alternative embodiment is shown in Fig. 5 in block diagrams.
According to this embodiment there are provided two separate branches,
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1638/1639~H/90
-17-
connected to the telephone line at connections 22 and 2~'. The upper
branch contains an attenuator 23, an isolation amplifier 24, and line
voltage analysis means, 25. The lower branch contains two
capacitances, 26 ancl 26', an isolation amplifier 27, and an AID
transducer.
The telephone line conveys to the interface of Fig. 5 two comblned
signals: the DC line voltage (up to about 200 V when ringing) and AC
information (about 1 V), carrying audio (speech and fax) information.
After attenuation at the attenuator 23, which as said is of the order of
50:1, the voltage can be transmitted through the isolation amplifier. At
this point the DC voltage can be analysed, but the A(: voltages are too low
for analysis. For this reason, in this embodiment of the invention there
is provided the lower branch, and the DC voltags is blocked by
capacitances 26 and 2~', while the audio signal is transmitted to a
second isolation amplifier 27, and then to an A/D device 28.
Alternatively, the system may operate as in Fig. 6, and the signal
attenuated by attenuator 29 can be passed, after isolation amplifier 30, to
a second branch and to amplifier 31, where the AC signal is amplified by
a factor of 50 and then fed to the A/D transducer 32.
The A/D transducer does not discriminate between speech and Çax
signals, but the modem can identify fax messages. Thus, it is possible to
control the operation of the A/I:) device according to the recognition of fax
signals based on the modem.
1638/:1~9/H/90
18-
In order to better understand the metllod of monitoring and analyzing
the activity of a telephone line, reference is made to Fig. 7, which shows
the activity of a telephone line from which a number is being dialed. The
normal voltage of the line, when no activity exists, is indicated by Vl.
This is the higher voltage which, nominally, is 48V. When the receiver
is lifted, the voltage drops very quickly to a lower value, V2, which
happens at to. The value of V2 is normally between 10 - 30V.
In Fig. 7 we see that the receiver has been lifted at to, dialing has beglm
at td~ and different digits are being dialed which reflect in pulses shown
in the figure. The first digit is a 3, as can be seen by three dif~erent
pulses of higher voltage. The time intervals tl and t2 are of 0.1 second or
less, and interval t3 is greater than 0.1 second, indicating that the first
group of pulses has ended. The first group includes three pulses, so that
the first digit is 3, the second group includes two pulses, so that the
second digit is 2. Further digits are not shown, for the sake of
simplicity.
According to the method of the invention, the value of Vl is sampled
continuously, and if no difference exists between two subsequently
calculated values ~within a predetermined tolerance), the last calculated
value becomes the reference value. When the receiver is lifted the
difference Vl V2 exceeds the predetermined maximal difference, as V2
is less than 80 - 85% of Vl, and recording of the activity of the line begins.
This recording will include all that happens from the time to onwards,
until such time as the voltage of the telephone line climbs again to a
16~8/~6~91~V90
-19-
value about the last r~corded value of Vl 1 and remains stable for a period
of time of several seconds. At that time the recoraing of the activity of
the telephone line stops.
It should be noted that, if desired, it is also possible to identify and record
incoming calls. When the telephone is ringing at the monitored end,
pulses of a higher and lower voltage are detected around the nominal Vl
value without any lower voltage base-line, because the receiver has not
been lifted. It is possible to start recording the activity of the telephone
line beginning with incoming calls, in addition to with the lifting of the
receiver. Then, when an incoming call is detected, if nobody lifts the
receiver recording will stop when the pulses about the nominal Vl
voltage stop and the voltage remains stable for a period of time of a
number of seconds. On the other hand, if the receiver is li~ted, then the
situation is like that depicted in Fig. 7, beginning at time to, and
recording will continue as described above.
It should be noted that most telephone exchanges employ the line-
reversal technique for outgoing calls to indicate the establishment of the
connection with the called party. In this technique, the line changes its
polarity at the instant in which the handset o~ the called party is lifted,
while preserving its absolute value. Since while sampling the line
voltage it is possible to determine its polarity, activating the recording
means can be delayed until the connection with the called party has been
established.
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1638/1639/~I/90
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As will be appreciated by a person skilled in the art, the method of the
invention is very convenient inasmuch as it "learns" the telephone line
it is monitoring, it permits to adjust the threshold value to the actual
value e~isting on the telephone line, even if this value changes with time
during the day or during a number of days, it frees the operator from the
need to control and manually set reference values, is reliable inasmuch
as it is based on a very large number of samplings, and it is easy and
simple to carry out, as it may utilize almost every normal
microcomputer available on the market.
As will be apparent to a person skilled in the art, it is possible to provide
very different arrangements of the various components of the apparatus
of the invention, in order to achieve the same results. For instance, it is
possible to provide a double interface, one for line voltage analysis and
one for the audio transmissions, although this is a more expensive
solution. Likewise, it is possible to employ dif~erent types of modems and
analogue-to-digital transducers, to connect them in different ways, to
change the order or type of elaboration of the va~ious signals, to provide
additional storage and/or retrieval and/or viewing means.
Furthermore, it is possible to provide many modi~lcations in the
monitoring and analysis method of the invention. For instance, it is
possible to activate another system, e.g., a loudspeaker, rather than
recording the con~ersation which is taking place on the telephone line,
although this is normally not advantageous. Likewise, it is possible
to connect devices which utilize the method of the invention to a
variety of outlets and recording or activating devices, to obtain
1~8/1639~H190 -21 -
dif~erent responses to an activity detected on the telephone line,
all without exceeding the scope of the in~ention.
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