JPS5819068A - Protection test system for subscriber line - Google Patents

Abstract

PURPOSE:To measure a resistance value with high accuracy, by providing a circuit with an impedance of which resistance value is greater than the maximum DC resistance value of a subscriber line itself and in which a signal transmission band frequency is inputted to one end of the subscriber line. CONSTITUTION:By using a DC loop resistance of a two-line subscriber line L2 limited to <=1.5kOMEGA, an impedance converting circuit 27 inserting a specific resistance value between a subscriber's data line terminator and the line L2 is provided and a DC resistance value of the line L2 viewed from a telephone office is shifted to different values. In normal two-line transmission, changeover switches 32 and 33 are switched to the line and are connected to the transmitter at the station via a transformer 26. At the maintenance work and test of the line L2, the switches 32 and 33 are changed over to the actual line and the line L2 is connected to a DC resistance value detection circuit 34. The circuit 34 flows a minute current to an object to be measured to measure the DC resistance. In this case, the total value of the resistance value specific to the line L2 and a resistor 30 of the impedance converting circuit 27 can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a maintenance test method for subscriber lines, and more particularly to an economical and highly accurate maintenance test method for subscriber lines in a two-wire digital subscriber transmission system.

Conventionally, in order to transmit data to subscribers via a telephone switching network, as shown in FIG. An analog transmission method is used in which this alternating current signal is converted back into a direct current data signal. In this case, the subscriber line is a two-wire line L2 including a signal converter (modem), and in FIG. An in-office data transmitting/receiving device H3 is connected.

This kind of analog transmission system subscriber line.

To perform a maintenance test, as shown in Figure 2, a 16 Hz current is sent from the central office to the telephone in the home, activating the R relay to generate a tone ringer sound, and returning it through capacitor C (12). This is done by detecting the current with the measuring circuit 35 and measuring the capacitance of the capacitor from the detected value. If the line is short-circuited in the middle, the capacitance of the capacitor O is O, and if it is cut in the middle of the line, the capacitance of the capacitor C is infinite.

Furthermore, recently, digital subscriber line transmission systems have been put into practical use, in which DC data signals are transmitted as they are in the baseband without converting them into AC signals.

In this method, as shown in Figure 3, data terminal equipment @1
A four-wire subscriber line L4 connects the in-home data line terminating device 2 connected to the in-home data line terminating device 2 and the in-office data line terminating device 3. The digital signal from the data terminal device 1 is converted into a code suitable for subscriber line transmission by the in-home data line termination equipment ft2, and then transmitted to the in-office data line termination equipment 3 via the + line type subscriber line. . Also, regarding digital signals from the communication partner, in exactly the same way,
Transmitted in the opposite direction to the above.

In such a four-wire subscriber line transmission system, when a line fault occurs, it is extremely important from the viewpoint of service to discover the faulty section early and reliably.

FIG. 4 is a diagram showing a maintenance test method for a four-wire subscriber line in a conventional digital data transmission system.

In Fig. 41, 7.8 is a digital signal input terminal;
6.9 digital signal output terminals, 10 to 14 are selector switches, 15 to 18 transformers, 19 are switches 10.
11 is a relay for switching, 20 is a DC current supply device, 21 is a maintenance test device transmitter, and 22 is a maintenance test device receiver.

First, by closing the switch 12, DC current is supplied from the DC current supply device 20 to the midpoint of the transformer of each 2-wire subscriber line of the 4-wire subscriber line, and both 2-wire subscriber lines and the relay 19 The relay 19 is operated by passing a direct current through the loop path through which the relay 19 is passed.

Due to the operation of relay 19, switches 10 and 11 are switched and connected as shown by the solid line in FIG. 4, so that transformer 15 is connected to transformer 16 via switch 10.11. Now that the maintenance test is ready, switch 1 is
3. The switch 14 is connected to a maintenance test device transmitter 21,
It is switched and connected to the maintenance testing device receiving section 22 side, and a sine wave signal is sent out from the maintenance testing device transmitting section 21. If the 4-wire subscriber line is normal, a sine wave signal is sent to the maintenance test equipment receiver via transformer 17.4-wire subscriber line 2, transformer 15, switch 10, transformer 16, and transformer 22. If a disconnection occurs or a short line occurs in the middle of each two-line subscriber line, the maintenance test device receiving section 22 cannot receive a sine wave signal, so that an abnormality can be determined.

By the way, in order to make subscriber lines economical, two-wire digital subscriber line transmission systems have recently been proposed (for example, JntGrnafJ-ona) (lonferen.
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In this system, since the subscriber line is two wires, a loop cannot be formed, and maintenance tests using a sine wave signal as shown in FIG. 4 cannot be performed. Furthermore, a maintenance test using a tone ringer sound as shown in FIG. 2 cannot be applied if a telephone is not provided in the house.

The purpose of the present invention is to solve such problems by providing an economical and highly accurate maintenance test for two-wire subscriber lines, including digital transmission systems, from the station side by simply providing a simple additional circuit. The purpose of the present invention is to provide a maintenance test method for subscriber lines that can perform maintenance tests on subscriber lines.

The subscriber line maintenance test method according to the present invention focuses on the fact that the DC loop resistance of the subscriber line is limited to a certain value or less, and uses a DC resistance value larger than the maximum DC resistance value of a single subscriber line, An impedance conversion circuit with an impedance that passes the transmission band frequency of digital signals or analog signals is installed at one end of the subscriber line, and the total DC resistance value of the subscriber line and the impedance conversion circuit is calculated at the other end of the subscriber line. It is characterized by being measured from

Embodiments and operating principles of the present invention will be described below with reference to the drawings.

FIG. 3 is an explanatory diagram of a maintenance test method for subscriber lines showing an embodiment of the present invention.

In Fig. 5, 23.24 is a digital signal input/output terminal, 25.26 is a transformer, 27 is an impedance conversion circuit, 28.29 is a capacitor, 30 is a resistor, 32.3
3 is a changeover switch, 34 is a DC resistance value detection circuit, and L is a two-wire subscriber line.

The present invention utilizes the fact that the DC loop resistance of a two-wire subscriber line is limited to less than 1.5 Ω, and utilizes the fact that a specific An impedance conversion circuit 27 into which a resistance value is inserted is installed to shift the DC resistance value of the two-wire subscriber line as seen from the telephone office to a different value.

When performing normal two-wire transmission, the changeover switches 32 and 33 shown in Figure 1 are switched to the dotted line side, and the transformer 2
When performing a maintenance test on the 2-line subscriber line connected to the station side transmission equipment via 6, the changeover switches 32 and 33 are switched to the solid line side, and the 2-line subscriber line L
2 is connected to the DC resistance value detection circuit 34. The DC resistance value detection circuit 34 measures the DC resistance value by passing a minute current through the object to be measured.
The sum of the values of the seven resistors 30 is measured.

FIG. 6 is a distribution diagram of DC resistance values of subscriber lines, showing the principle of the maintenance test method shown in FIG.

Now, assuming that the resistance value of the resistor 30 of the impedance conversion circuit 27 is R, the DC resistance value of the two-wire subscriber line as seen from the telephone office is distributed between R and l+1°5.

The resistance of a subscriber line varies depending on the material and signal frequency; for a pair cable with a polyethylene jacket, it is about 600 Ω in the voice frequency band, about 110 Ω in the high frequency band of 50 to 100 KHz, and about 110 Ω in the case of direct current. Although it varies depending on the distance, it is limited to a maximum of 1.6 Ω.

Therefore, as shown in FIG.
If the distribution of the single loop resistance value is A of 0 to 1.5 Ω, the distribution of the DC resistance value when the impedance conversion circuit 27 is inserted is R ~ (R + 1.5 KΩ)
(7) It will be shifted to position B.

If there is a short circuit between the lines in the middle of the 2-line subscriber line, no matter where the short circuit is at any point on the 2-line subscriber line, the 2-line subscriber line as seen from the telephone office will railroad,
The DC resistance value is the range path A in Figure 6 (Ω from 0 to 1.5).
) and can be clearly distinguished from the range B, so the DC resistance value detection circuit 34 can easily detect a short circuit fault.

Further, when the two-wire subscriber line is disconnected, the resistance value displayed by the DC resistance value detection circuit 34 becomes infinite, so that it can be clearly distinguished from the range B.

As shown in FIG. 6, in order to prevent the ranges A and B from overlapping, it is necessary to set at least the resistance value R of the resistor 30 of the impedance conversion circuit 27 to 1.5 KΩ or more. be.

As mentioned above, digital subscriber line transmission usually consists of a line "110" and a Q system, so if the resistance value R is set sufficiently higher than this value, the effect on digital transmission can be ignored. For example: , the resistance value R of resistor 30 is 1 OK
It is sufficient to set it to about Ω.

Further, as the capacitors 2δ and 29 of the impedance conversion circuit 27 in FIG. 5, capacitors with sufficiently high capacitance values are used in order to avoid giving the upper form t of digital transmission. Note that when DC power is supplied to the in-home data line termination device 2 from the telephone office via a two-line subscriber line, the capacitors 28 and 29 of the impedance conversion circuit 27
are necessary for separating the DC power supply voltage and the digital signal, but when using a power supply system other than IR, the capacitors 28 and 29 become unnecessary. Therefore, the new parts required for maintenance tests on 2-line subscriber lines are:
There is only a resistor 30.

Further, in FIG. 5, the impedance conversion circuit 27 is constructed of a resistor 30 and capacitors 28 and 29, but of course other impedance elements can be used.

Next, although FIG. 6 describes the case where the present invention is applied to a digital two-wire subscriber line transmission system, it is also applicable to a two-wire subscriber line transmission system for analog signals. Furthermore, if two impedance conversion circuits are used, 4
It can also be applied to a wire subscriber line transmission system.

As explained above, according to the present invention, by simply inserting a simple additional circuit into one end of the subscriber's line, for example inside the house,
Maintenance tests on the subscriber line can be performed directly from the telephone office power at the other end, and by measuring the DC resistance value of the subscriber line at that time, it is possible to detect faults such as 1#: N short circuit in the middle of the subscriber line. Since it is possible to determine whether or not there is a problem, it is possible to conduct a test with high accuracy and accuracy. Moreover, it is applicable not only to the 21vlI digital subscriber transmission system but also to the 4-wire subscriber transmission system and the 2-wire analog subscriber transmission system.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a subscriber line transmission system using a conventional analog transmission method, Figure 2 is a diagram showing a maintenance test method for the subscriber line in Figure 1, and Figure 3 is a diagram of a conventional digital subscriber line transmission system. FIG. 4 is a diagram showing the maintenance test method for the line subscriber line shown in 4 of FIG. 3, and FIG. FIG. 6 is a distribution diagram of the direct current resistance value of the subscriber line, showing the principle of FIG. 1: Data terminal equipment, 2: In-home data line termination equipment, 3
: In-office data line termination equipment, 5-doubles converter (modem)
, 6.91 Digital signal output terminal αυ terminal, 7.8: Digital signal input terminal, 10~14°3
2, 33: Changeover switch, 15-18, 25. 26: Transformer, 19 word relay, 20: DC current, current supply device, 21: Maintenance test device transmitter, 22: Maintenance test device receiver, 23, 24: Digital signal input/output terminal, 27
: Impedance conversion circuit, (12) 1W, 4

Claims (1)

[Claims] At one end of the subscriber line, an impedance conversion circuit having an impedance whose DC resistance value is larger than the maximum DC resistance value of the subscriber line itself and through which the signal transmission band frequency passes is installed, and the impedance conversion circuit is installed at one end of the subscriber line. A maintenance test method for a subscriber line, characterized in that the total DC resistance value of the subscriber line and the impedance conversion circuit is measured by supplying a DC current from the end of the subscriber line.