Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a method for testing
communication paths of an electronic telephone exchange
which has a pair of time-sharing communication highways,
one for receiving signals and the other for transmitting
signals.
The communication paths of an electronic exchange
are automatically tested before connecting paths in
every time or tested at regular intervals. For example
the communication paths of an exchange of time-sharing
type are conventionary tested by supplying test signal
all the time or at regular intervals in a loop back
circuit through the communication highways. Such a use
of the loop back circuit renders the exchange even more
complicated and even more expensive. Further, these
methods are disadvantageous in that they can not test
the analog signal processing units of the communication
circuit, such as line circuits or trunk circuits.
An object of this invention is to provide a method
for testing communication paths of an electronic exchange
which has at least a pair of time-sharing communication
highways, without using a specially designed hardware.
Another ob~ect of this invention is to provide a
method for testing the total communication paths of an
electronic exchange including both the time-sharing
communication highways and line circuits and trunk
circuits of the communication paths.
According to this invention there is provided a
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method for testing communication paths of an electronic
exchange which has at least a pair of time-sharing
communication highway and a plurality of port circuits
which are connected to one another in time-sharing fashion
through the first and second communication highways.
The inventioned method comprising a first step of
detecting at least one of the port circuits which can
transfer input signals from the first communication
highway to the second communication one; a second step
of transferring a test signal to at least one of the
port circuits being detected in the first step through
the first communication highway, during time slot
allotted to the port circuit; a third step of causing
said port circuit to deliver the test signal and storing
the test signal into memory means through the second
communication highway; a fourth step of reading out the
test signal from the memory means through the second
communication highway to receiving means, during time
slot allotted to the receiving means; a fifth step of
converting the test signal into a coded signal; and a
sixth step of generating a detection signal in the ivent
the coded signal is not detected within a predetermined
time after the test signal has been transferred in the
second step.
This invention can be more fully understood from
the following detailed description when taken in con-
junction with the accompanying drawings, in which:
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Fig. l is a block circuit diagram of the communi-
cation paths of an electronic exchange to which a
method according to this invention is applied;
Fig. 2 is a block circuit diagram of a line circuit
used in the communication paths of Fig. l;
Fig. 3 is a block circuit diagram of a trunk circuit
used in the communication paths of Fig. l;
Fig. 4 is a block circuit diagram of a dual tone
multi-frequency signal receiving circuit used in the
communication paths of Fig. l;
Figs. 5A to 5K are time charts schematically showing
how signals at various parts of the communication paths
of Fig. 1 are allotted to time slots; and
Fig. 6 is a block circuit diagram of a paging trunk
circuit used in the communication paths of Fig. 1.
Fig. 1 shows the communication paths of a PCM (pulse
code modulation) exchange which cln connect the touch tone
dial telephone to which an embodiment of this invention
is applied. The paths are provided with a central control
unit lO. The unit 10 comprises a CPU (central processor
unit) l, a serial input/output (S I/O) 2, a memory 3,
a magnetic cassette tape 4 and a parallel input/output
(P I/O) 5. The memory 3 keeps storing the operation
program of the CPU 1 only while it i5 turned on. Thus,
the operation program of the CPU 1 is permanently
recorded on the cassette tape 4.
The communication paths are further provided with
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line circuits 12-1 to 12-N, line circuit 14-1 to 14-N,
trunk circuits 16-1 to 16-P and dual tone multi-frequency
signal (which is hereinafter referred to as DTMF siynal)
receivers 18-1 to 18-Q. Various detection signals from
these circuits 12, 14, 16 and 18 are supplied to the
S I/O 2 through a transmission data highway 20, serially
one after another. The S I/O 2 supplies the detection
signals to the CPU 1 in parallel fashion, that is, at
the same time. On the other hand, control signals from
the CPU 1 in parallel fashion are transferred through
the S I/O 2 and P I/O 5. The S I/O 2 converts the
control signals into series signals, which are supplied
via a reception data highway 22 to the line circuits 12-1
to 12-N, line circuits 14-1 to 14-N, trunk circuits 16-1
to 16-P. The P I/O 5 supplies the control signals to a
tone signal generator 24, a selector 26 and a buffer
memory 28 in parallel fashion.
The tone signal generator 24 stores coded data.
These data represent a dial tone signal which is
transmitted to a telephone when the receiver thereof
is picked up, a DTMF signal which is transmitted via
one of the trunk circuits to the central office from
a call station when the caller operates a telephone
dial, a busy tone signal which is transmitted back to
the call station when the called station is busy, and
other similar signals. The generator 24 produces these
signals according to the control signals from the CPU 1.
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The output signal of the tone signal generator 24 is
supplied to one input terminal of the selector 26.
Voice signals from the line circuits 12-1 to 12-N
are supplied via a transmission highwa~ 34 to a first
input terminal of a multiplexer 32. Voice signals
from the line circuits 14-1 to 14-N are supplied via
another transmission highway 36 to a second input
terminal of the multiplexer 32. Voice signals from
the trunk circuits 16-1 to 16-P are supplied via still
another transmission highway 38 to a third input
terminal of the multiplexer 32. The multiplexer 32 once
latches the three voice signals and then supplies them
serially to the other input terminal of the selector 26
at a speed three times higher than the speed at which
it received the three voice signals. The selector 26
supplies the output signal of the tone signal generator
24 or the output signal of the multiplexer 32. The
output signal of the selector 26 is supplied to the
buffer memory 28. In the buffer memory 28 the time
slots are replaced with one another, and from the buffer
memory 28 the output signal of the selector 26 is read
out. The output signal of the memory 28 is supplied to
the signal distributor 30. The distributor 30 supplies
this signal via a reception highway 40 to the line
circuits 12-1 to 12-N, via a reception highway 42 to the
line circuits 14-1 to 14-N, and via a reception highway ..
44 to the trunk circuits 16-1 to 16-P and the DTMF signal
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receivers 18-1 to 18-Q. P and Q are so selected that the
sum of P+Q is equal to N.
In the communication paths of Fig. 1, three pairs
of highways are provided, a first pair consisting of the
highways 34 and 40, a second pair consisting of the
highways 36 and 42 and the third pair consisting of the
highways 38 and 44. The line circuits 12-1 to 12-N are
connected to the highways 34 and 40, the line circuits
14-1 to 14-N to the highways 36 and 42, and the trunk
circuits 16-1 to 16-P and DTMF signal receivers 18-1 to
18-Q to the highways 38 and 44. The circuit arrangement
is not limited to this manner. For example, the line
circuits 12-1 to 12-N may be connected to the highways
38 and 44, and the trunk circuits 16-1 to 16-P may be
connected to the highways 34 and 40. Further, all the
circuits 12, all the circuits 14, all the circuits 16
and all the receivers 18 need not be connected to the
corresponding pairs of highways. For instance, some of
the line circuits 12-1 to 12-N may be connected to the
highways 34 and 40. Moreover, less or more than three
pairs of highways may be provided. In this case, the
signal-reading speed of the multiplexer 32 is varied
according to the number of highway pairs provided.
Now referring to Figs. 2, 3 and 4, the line circuits,
trunk circuits and DTMF signal receivers will be
described.
Fig. 2 shows the line circuit 12-1, which has the
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same structure as the other line circuits 12 2 to 12-N~
As shown in Fig. 2, the voice signal from the reception
highway 40 is supplied to a PCM coder/decoder (herein-
after called "codec") 50 and undergoes digital-to-analog
conversion. The analog signal thus obtained is supplied
to a lowpass filter 52 and has its waveform rectified.
The output of the filter 52 is supplied to one end of
one winding of a hybrid transformer 54. Another winding
of the transformer 54 is connected via a changeover
switch 56 to a touch tone dial or rotary dial telephone
~not shown). The movable contact of the switch 56 is
connected to the telephone. First and second fixed
contacts of the switch 57 are connected to the trans-
former 54 and a ringing signal generator (not shown),
respectively. The changeover switch 56 is controlled by
an actuator 59 which is in ~urn controlled by a control
signal supplied from the CPU 1 via the data highway 22
and an S I/O 58. To the winding of the transformer 54,
which is disposed on the telephone side, there is
connected a off-hook detector 60 the output of which is
supplied to the transmission data highway 20. The voice
signal from the telephone is supplied to the codec 50
through the hybrid transformer 54 and a lowpass filter
62. The codec 50 converts the voice signal (i.e. analog
signal) into a digital signal, which is transmitted
through the transmission highway 34. All the line
circuits 12-1 to 12-N and 14-1 to 14-N are not connected
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to telephones, so that more telephones may be connected
to the exchange if necessary in the future.
Fig. 3 shows the trunk circuit 16-1, which has the
same structure as the other trunk circuits 16-2 to 16-P.
5 As shown in Fig. 3, the voice signal from the reception
highway 44 is supplied to a codec 64 and undergoes
digital-to-analog conversion. The analog signal thus
produced is supplied to a lowpass filter 66 and has its
waveform rectified. The output of the filter 66 is
10 supplied to one end of one winding of a hybrid transformer
68. The other winding of the transformer 68 is connected
via a switch 70 to a central office (not shown). The
switch 70 is controlled by an actuator 76 which is in
turn controlled by a control signal supplied from the
CPU 1 through the data highway 22 and an S I/O 74,
thereby to constitute a loop jointly with the central
office. To the winding of the hybrid transformer 68,
which is provided on the central office side, there is
connected an incoming detector 72. The voice signal
supplied from the central office is supplied to the
codec 64 through the transformer 68 and a lowpass filter
74. The codec 64 converts the voice signal (i.e. analog
signal) into a digital signal, which is transmitted
through the transmission highway 38. All the trunk
circuits 16-1 to 16-P need not be connected to the
central office, so that more telephones may be connected
to the exchange if necessary in the future.
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Fig. 4 shows the DTMF' signal receiver 18-1, which
receives an address signal from the telephone having a
DTMF dial and has the same structure as the other DTMF
signal receivers 18-2 to 18-Q. As shown in Fig. 4, a
DTMF signal from the reception highway 44 is supplied to
a codec 78 and is converted into an analog signal, which
is supplied to a highpass filter 80 and a lowpass filter
82. The highpass filter 80 delivers the high frequency
component of the DTMF signal, and the lowpass filter 82
the low frequency component thereof. A pair of output
signals of the filters 80 and 82 are supplied to a DTMF
signal detector 84. The DTMF signal detector 84 detects
a DTMF signal which consists of a high frequency com-
ponent and a low frequency component. It translates
the DTMF signal into a dial numerical code. The dial
numerical code is supplied to an S I/O 86 and converted
into serial signals, which are transmitted to the central
control unit 10 through the transmission data highway 20.
Now it will be described how the PCM exchange shown
in Fig. 1 operates in case the line circuit 12-1 is
connected to the trunk circuit 16-1, the line circuit
14-1 is connected to the line circuit 12-N, the tone
signal generator 24 supplies a dial tone signal to the
line circuit 14-N, and a DTMF signal is supplied to the
DTMF signal receiver 18-Q. In this case, it is necessary
to transfer a voice signal between the line circuit 12-1
and the trunk circuit 16-1 and a voice signal between the
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line circuit 14-1 and the line circuit 12-N. To achieve
this, the line circuits 12-1 to 12-N are connected to
the highways 34 and 40, and the line circuits 14-1 to
14-N to the highways 36 and 42. The signals from the
line circuits 12-1 to 12-N are allotted to 1st to Nth
time slots of the highways 34 and 40. Similarly, the
signals from the line circuits 14-1 to 14-N are allotted
to 1st to Nth time slots of the highways 36 and 42. The
trunk circuits 16-1 to 16-P are connected to the trans-
mission highway 38, and the signals from the trunk
circuits 16-1 to 16-P are allotted to 1st to Pth time
slots of the highway 38. Thus, no signals are allotted
to (P+l)th to Nth time slots of the highway 38. The
trunk circuits 16-1 to 16-P and the DTMF signal
receivers 18-1 to 18-Q are connected to the reception
highway 44. Here, P+Q = N. The signals to the circuits
16-1 to 16-P are allotted to 1st to Pth time slots of
the highway 44, and the signals to the receivers 18-1
to 18-Q are allotted to (P+l)th to Nth time slots of the
highway 44, respectively.
More specifically, the signals at the various
parts of the communication paths of Fig. 1 are allotted
to time slots of the highways as illustrated in Figs. 5A
to 5K.
Fig. 5A shows 1st time slot Tl to Nth time slot T .
Fig. 5B shows what signals are allotted to the time slots
of the highway 34~ Fig. 5C shows what signals are
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allotted to the time slots of the highway 36. Fig. 5D
shows what signals are allotted to the time slots of
the highway 38. As Figs. 5A to 5D indicate, a voice
signal Al from the line circuit 12-1, a voice signal B
from the line circuit 14-1 and a voice signal C1 from
the trunk circuit 16-1 are allotted to the 1st time
slots Tl of the highways 34, 36 and 38, respectively.
Voice signals An and Bn from the line circuits 12-N and
14-N are allotted to the Nth time slots Tn of the high-
ways 34 and 36 r respectively. No signal is allottedto the Nth time slot Tn of the highway 38.
The voice signal Al is a PCM code obtained by
removing the high frequency component of a signal from
the telephone by means of the lowpass filter 62, by
sampling the signal by means of the codec 50 and by
converting the signal (i.e. analog signal) into a digital
signal. The voice signal Cl is also a PCM code obtained
by removing the high frequency component of a signal
from the delay line by means of the lowpass filter 74
and by converting the signal (i.e. analog signal) into
a digital signal. The voice signal from each of the
circuits 12-1 to 12~N, 14-1 to 14~N and 16-1 to 16-P
is constituted by 8 bits, which is transmitted through
the transmission highways 34, 36 and 38 during a slot
time.
The multiplexer 32 receives the signals coming
through the transmission highways 34, 36 and-38, latches
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them for a while and deliver them at a speed three times
higher than it received the signals. Thus, as shown in
Fig. 5E, a signal supplied throuyh the highway 34 is
allotted to the first one-third of each time slot, a
signal supplied through the highway 36 to the second
one-third of each time slot, and a signal supplied through
the highway 38 to the last one-third of each time slot.
That is, to the 1st time slot Tl the voice signals Al,
Bl and Cl from the circuits 12-1, 14-1 and 16-1 are
allotted. In a similar manner, dial tone signals Xl to
Xn 1 and a DTMF signal XFn are allotted to the time
slots Tl to Tn, three to each time slot, as illustrated
in Fig. 5F.
The selector 26 supplies to the buffer memory 28
the output signals (Fig. 5E) of the multiplexer 32 and
the tone signal generator 24 selectively so as to
deliver signals in such a way as illustrated in Fig. 5G.
That is, the selector 26 delivers all the output signals
of the multiplexer 32 but the voice signal Bn from the
trunk circuit 16-N and then delivers the dial tone
signal Xn 1 and the DTMF signal XFn from the tone signal
generator 24. As a result, the voice signals Al, Bl and
Cl are allotted to 1st time slot Tl, and the voice signal
An, which is to be exchanged, the dial tone signal Xn 1
and the DTMF signal XFn to Nth time slot Tn. The
output signals of the selector 26 are stored into the
buffer memory 28, byte by byte, each byte into the
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corresponding address.
The signals are read out from the buffer memory 28
in such a way as to be transmitted through the reception
highway 40, 42 or 44 which is connected to the called
station, during the time slot allotted to the called
station. More precisely, to connect the line circuit 12-1
to the trunk circuit 16-1, in the 1st time slot Tl the
voice signal Al from the line circuit 12-1 and the voice
signal Cl from the trunk circuit 16-1 exchange their
positions according to a control signal from the CPU 1 as
shown in Fig. 5H. Further, to connect the line circuit
14-1 to the line circuit 12-N, the voice signal An from
the line circuit-12-N and the voice signal Bl from the
line circuit 14-1 exchange their positions as illustrated
also in Fig. 5H. Moreover, to supply the dial tone
signal Xn 1 and the DTMF signal XFn to the line circuit
14-N and the D1'MF signal receiver 18-Q, respectively,
these signals Xn 1 and XFn are allotted again to the
second one-third and last one-third of the Nth time slot
Tn as shown in Fig. 5H.
The signal distributor 30 distributes the output
signals of the buffer memory 28 to time slots of the
reception highways 40, 42 and 44 as illustrated in
Figs. 5I, 5J and 5K. That is, the signal allotted to
the first one-third of each time slot is transmitted
through the highway 40, the signal allotted to the
second one-third of each time slot through the highway 42,
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1~3089~3
and the signal allotted to the last one-third of each
time slot through the highway 44. Consequently, the
line circuit 12-1 and the trunk circuit 16-1 are
connected to each other, the line circuit 14-1 and the
line circuit 12-N are connected to each other, and the
dial tone signal Xn 1 and the DTMF signal XFn both
from the tone signal generator 24 are supplied to the
line circuit 14-N and the DTMF signal receiver 18-Q,
respectively.
Now it will be described how to test the communi-
cation paths of the PCM exchange shown in Fig. 1 to
Fig. 4.
First, a DTMF signal is supplied to the DTMF signal
receiver 18-Q in the above-described manner. The receiver
18-Q converts the DTMF signal into a dial code signal.
The dial code signal is supplied to the S I/O 86 and
converted into parallel signals, which are transferred
to the CPU 1 via the transmission data highway 20. If
both the reception highway 44 and the transmission data
highway 20 work normally, the CPU 1 receives a dial
code signal a predetermined time after it has supplied
a control signal to the tone signal generator 24 to make
the same to produce a DTMF signal corresponding to the
dial code signal. If the highway 44 or the highway 20
fails to work normally, the CPU 1 cannot receive a dial
code signal even after the predetermined time has lapsed.
In this way, the highways to which the DTMF signal
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receiver 18-Q are tested, and it is found whether or
not they work normally.
If both highways to which the DTMF signal receiver
18-Q is connected are found to work, then some or all of
the other highways are tested. For example, the CPU 1
detects those of the line circuits 12-1 to 12-N, 14-1
to 14-N, trunk circuits 16-1 to 16-P which are idle.
The CPU 1 detects the line circuits which are idle,
according to the detection signals from the off-hook
detectors 60. It detects the trunk circuits which are
idle, according to the detection signals from the
received signal detectors 72. Each highway can be
tested only if at least one of the circuits connected
to it is idle. If all the circuits connected to each
highway are used, it would not matter. One circuit or
two become idle a few seconds later, and the highway
can then be tested because the test according to this
invention can be carried out at any time as long as
at least one of the circuits connected to the highway
is idle. To supply a DTMF signal from the generator 24
to the circuit which is idle, the CPU 1 supplies a
control signal to the tone signal generator 24, the
selector 26 and the buffer memory 28. The control
signal causes the generator 24, the selector 26 and
the memory 28 to form a circuit for supplying the DTMF
signal to the idle circuit, a circuit for connecting
the idle circuit to the other idle circuits and a circuit
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for connecting one of the id]e circuits to the DTMF
signal receiver 18-Q.
The auxiliary line circuits and the trunk circuits
are always idle. The other general line circuits and
trunk circuit are idle only when the telephones are
on-hook or when the switches 70 are not closed. The
hybrid transformers 54 of the line circuits are in
matching state when the telephones 56 are off-hook.
The hybrid transformers 68 of the trunk circuits are
in matching state when the switches 70 are closed.
The transformers 54 and 68 have the maximum return loss
of about 20-30 dB when they are in matching state.
When they come out of matching state, the hybrid
transformers 54 and 68 have a smaller return loss.
Thus, a DTMF signal from the tone signal generator 24
is not received by the telephones of the idle line
circuits or by the central office connected to the idle
trunk circuits. It is therefore supplied from the idle
line circuits or the idle trunk circuits to the DTMF
signal receiver 18-Q through all or some of the trans-
mission highways and the reception highway 44.
If the line circuit 12-1, the line circuit 14-1 and
the trunk circuit 16-1, for example, are idle, the DTMF
signal is transferred to the DTMF signal receiver 18-Q
through the highway 40, the line circuit 12-1, the
highway 34, the multiplexer 32, the signal distributor
30, the highway 42, the line circuit 14-1, the highway 36,
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the multiplexer 32, the signal distributor 30, the
highway 44, the trunk circuit 16-1, the highway 38,
the multiplexer 32, the signal distributor 30 and the
highway 44. When the CPU 1 receives the dial signal,
it is ascertained that the highways work in a desired
manner. If it does not receive the dial signal, the
highways are considered not to work in a desired manner.
In case the highways are found not to work in a
desired manner, each pair of highways is then tested.
That is, the highways 34 and 40, the highways 36 and 42
and the highways 38 and 44 will be tested. To test each
pair of highways, the CPU 1 forms a communication path
consisting of, for example, the highway 40, the line
circuit 12-1, the highway 34, the multiplexer 32, the
signal distributor 30, the highway 44, and the DTMF
signal receiver 18-Q. If any one of the highway pairs
is found not to function in a desired manner, a DTMF
signal is transferred through said communication path,
allotted to a different time slot. The DTMF signal is
allotted to a different time slot in order to ascertain
which part has failed to pass the previously applied
signal, the analog signal processing units of the
line circuits or the trunk circuits, the DTMF signal
receivers, the pair of highways themselves, or the
buffer memory 28. If this test, wherein the DTMF
signal is allotted to a different time slot, shows that
the pair of highways function in a desired manner, then
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the highways are found to be functioning correctly,
while the analog signal processing units and/or the
buffer memory 28 is found to be functioning erroneously.
As mentioned above, the method according to invention
tests the communication paths of a PCM exchange in, so to
speak, two steps. First, it tests the communication
paths. Second, even if the communication paths are
found to work, each of the highway pairs is tested, using
a DTMF signal allotted to a different time slot. This
two-step serves to achieve a test of the communication
paths including the analog signal processing units and
the buffer memory of the PCM exchange. The results of
the test may be display by, for example, an alarm lamp.
Since it utilizes a few of the circuits which are idle,
the test can be conducted almost whenever desired,
without using a specially designed hardware.
If the telephone of, for example, the line circuit
12-1 which is idle and to which a DTMF signal is supplied
from the tone signal generator 24 happens to come into
off-hook state during the test, the off-hook detector
60 of the circuit 12-1 supplies a detection signal to
the CPU 1 via the transmission data highway. Upon
receipt of the detection signal, the CPU 1 cuts the
circuit loop for conducting the test, thus stopping
the test so that the telephone can be used.
To test the data highways 20 and 22, the CPU 1
supplies interrogation signals to the line circuits,
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the trunk circuits and the DTMF signal receivers.
Further, at least one of the trunk circuits 16-1
to 16-P may be replaced by such a paging trunk circu.its
as shown in Fig. 6. The paging trunk circuit only
receives voice signals. In the paging trunk circuit,
a codec 100 converts a voice signal from the reception
highway 44 into an analog signal, which is supplied via
a lowpass filter 102 to the fixed contact of a changeover
switch 104. The first movable contact of the switch 104
is connected to one winding of a transformer 106. The
second movable contact of the switch 104 is connected to
the transmission highway 38 through the codec 100. The
winding of the transformer 106 is connected to an paging
amplifier (not shown~. The switch 104 is controlled by
an actuator 110 which is in turn controlled by a control
signal supplied from the CPU 1 through the reception
data highway 22 and an S I/O 108. Usually the switch
104 is switched to the first movable contact and is thus
connected to the transformer 106. It is switched to the
second movable contact only when the test is to be
conducted. As long as the switch 104 is switched to
the second movable contact, the paging trunk circuit
delivers a DTMF signal from the tone signal generator 24
through the transmission highway 38. Thus, the communi-
cation paths can be tested by using the paging trunkcircuits as idle circuits, only if the communication
paths are so designed as to transfer the dial signal
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~rom the paging trunk circuits to the DTMF signal
receiver 18-Q.
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