JPS62293864A - Subscriber system transmission circuit testing system - Google Patents

Abstract

PURPOSE:To accurately execute the test of a subscriber system transmission circuit in a short time in the case where the state of deterioration of characteristic occurs only stochastically by making the pulse peak value of a transmission pulse signal lower than an ordinary standard value at the time of testing the transmission circuit. CONSTITUTION:When the sending level of a transmission pulse signal is made small by making the value of resistance of a variable resistance circuit 12 inserted between a pulse voltage input terminal 103 and an output transformer 11 a limited value, it means that line loss is effectively increased. Here, a switch 13 is made open only at the time of testing, and the upper limit of the variable resistance circuit 12 is made up to a value that make the effective line loss at the time of testing the transmission circuit designed upper limit value of this transmission system or a value obtained by adding a design margin value to it. Under such condition, if the transmission circuit is in the normal state, measured code error rate becomes lower than a desined target value, and when the transmission circuit has a fault, code error rate at the time of normal use can be estimated by a code error rate characteristic curve for line loss obtained in the same kind of equipments, lines, etc.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a subscriber transmission line that automatically tests a digital subscriber transmission line that transmits and receives coded pulses from the network side. Concerning the test method.

[Conventional technology]

Conventionally, in order to test subscriber transmission lines that transmit information by sending and receiving coded pulses, as shown in Figures 6 (al and (b)), access functions from the network side have been installed and There is a method in which loop return is performed in the installed line termination device 2. With this method, the presence or absence of a failure between the line termination device 2 including the subscriber line 3 and the terminal station device 4 can be determined based on the code error occurrence rate.

[Problem that the invention seeks to solve]

However, for example, if the deterioration of the characteristics is at an amount that the user would consider to be a failure or is close to the transmission system design deterioration limit, the results may not be unacceptable even if the above test is performed in response to a report from the user. In most cases, failure conditions can only be determined probabilistically (usually by conducting long-term tests). In other words, the conventional method has the drawback that it can only detect when a failure occurs regularly, and it is almost impossible to detect when a failure state occurs stochastically.

An object of the present invention is to eliminate the above-mentioned drawbacks, thereby making it possible to perform tests on subscriber transmission lines in cases where characteristic deterioration occurs only stochastically, without requiring a long time and in the same amount of time as in the past. It is an object of the present invention to provide a subscriber system transmission line testing method that is possible to detect degraded conditions more clearly.

[Means for solving problems]

A first aspect of the present invention is to measure the transmission characteristics of a digital subscriber system transmission line including a line termination device and an end station device connected via a subscriber line to the transmission transmitted from the end station device during a test. In a subscriber transmission line test method in which a pulse signal is tested by returning the pulse signal at the line termination device and detecting its code error rate, the pulse height value of the transmitted pulse signal is specified in the digital subscriber transmission line during the test. It is characterized by being lower by a predetermined value than the normal standard value.

In addition, the first invention of the present invention is such that the reduction value vo (V) of the pulse peak value of the transmitted pulse signal during the test is determined by the following formula, where E is the standard value of the pulse peak value of the transmitted pulse signal during normal use. (V), La: Transmission line line loss (dB) of the test object, La
5x: line loss (dB) greater than the design upper limit of the transmission line line loss to be tested, preferably determined according to the following.

A second aspect of the present invention is to measure the transmission characteristics of a digital subscriber system transmission line including a line termination device and a terminal device connected via a subscriber line, by measuring the transmission characteristics of a digital subscriber system transmission line that is transmitted from the terminal device during a test. In the subscriber system transmission line 'fa test method, which tests the pulse signal by looping back the pulse signal at the line termination device and detecting its code error rate, the pulse peak value of the above-mentioned transmission pulse signal is measured at the time of the test by returning the pulse signal to the digital subscriber system transmission line and detecting its code error rate. The present invention is characterized in that the code error rate is tested using the transmission pulse signals having at least two different reduction values lower than the normal standard value defined in .

[For production]

In the present invention, in order to forcibly make a steady state of deterioration noticeable when a deterioration state occurs only stochastically, the level of the transmission pulse signal of the transmission line ( pulse wave height value). For example, FIG. 4 shows the relationship between the line loss and the transmission line code error rate when a metallic line is used for the subscriber line. As is clear from this figure, the code error rate worsens as the line loss increases. As a result, if the line loss is the same (usually it is not practical to increase the loss by changing subscriber lines during testing), by lowering the transmission level of the transmission pulse signal, code errors can be avoided. The deterioration of the characteristics of this transmission line during normal operation can be detected using the values obtained under such conditions, for example, using the line and bit error rate characteristic curves shown in FIG.

FIG. 5 is a characteristic diagram showing an example of actually measured code error occurrence intervals in a 64 Kb/s path in a two-wire time-division direction controlled transmission system using metallic wires. The bit error rate decreases as the applied line loss value increases.

In other words, the code error occurrence interval is reduced. This occurrence interval becomes exponentially shorter as the line loss value increases, resulting in a significant reduction in the code error measurement time. 64K above
In the case of b-8 passes, the average occurrence interval when one bit error occurs is 2.6 minutes for a code error rate of lXl0-', which is a sufficiently practical test time.

The above example is a situation in a normal state, and in a faulty state, l/
A test time of 10 to 1/100 is sufficient. That is,
Stochastic deterioration events can be tested in a shorter time than conventional methods.

In other words, conventionally, in order to understand stochastic deterioration events, long test times were taken to detect them (in reality, long-term tests cannot be performed, and failure conditions cannot be confirmed with short-time tests).
In contrast, in the present invention, it is possible to forcibly create conditions for frequent code errors and to detect this event in the same amount of time as in the past.

Furthermore, by specifying the reduction value of the pulse peak value of the test pulse signal so that the line loss of the transmission circuit is equivalently equal to the design upper limit value or a value obtained by adding a margin value to the design upper limit value, the above-mentioned The internal deterioration event of the flll can be grasped more accurately.

In addition, by testing each transmission pulse signal in which the drop value of the pulse peak value of the test pulse signal is set to at least two different values, and finding the relationship between the drop value and the bit error rate, the transmission line under test is tested. Accurate bit error rates that are not affected by variations in line loss can be obtained.

〔Example〕

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

6(al) and (b) are block diagrams showing the configuration of a digital subscriber system transmission line to which an embodiment of the present invention is applied. FIG. 6(a) shows the normal state and FIG. indicates the time of testing.The transmission characteristics of the digital subscriber system transmission line including the line termination device 2 and the terminal device 4 connected via the subscriber line 3 are compared to the subscriber line connected to the terminal device 4. A test pulse signal is sent from the signal transmitter 6 of the test circuit 5, looped back by the line termination device 2 as shown in FIG. It is designed to detect the rate.

FIG. 1 is a circuit diagram showing the main part of the transmission pulse signal output circuit of the line termination device 2 or the terminal station device 4, and only the basic components related to the operation of the present invention are shown. In FIG. 1, 11 is an output transformer, 12 is a variable resistance circuit, 13 is a switch, 14 is a drive element system, 101 and 102 are output terminals, 103 is a pulse voltage input terminal, and 104 is a control voltage terminal (these A component may also be a component at the time of receiving a transmitted pulse). Figure 1 shows AMT (8 Iternate Mark Inve
In this example, the pulse peak value (sending level) of the transmission pulse signal to be sent out is determined by the magnitude of the voltage applied to the pulse voltage input terminal 103. Therefore, by setting the resistance value of the variable resistance circuit 12 inserted between the pulse voltage input terminal 103 and the output transformer 11 to a finite value, the sending level of the transmission pulse signal can be reduced and line loss can be effectively reduced. It means that it has increased. Here, the switch 13 is opened only during testing, and the variable upper limit of the variable resistance circuit 12 is
The effective line loss during testing of this transmission line shall be up to the design upper limit value of this transmission method or the value obtained by adding the design margin value to that value. In this situation, if this transmission line is in a normal state, the measured bit error rate will be below the design target value, and if this transmission line is out of order, the code error rate shown in Figure 4 above, obtained in advance using similar equipment and lines, etc. The bit error rate during normal use can be estimated from the bit error rate characteristic curve with respect to loss. The variable resistance circuit 12 is controlled by an automatic gain control amplifier in the receiving circuit (a line termination device must be installed at any subscriber's home without adjustment, and in order to be able to cope with any line loss, (A line is provided to keep the embodiment constant.) Determine the additional line loss value, that is, the resistance value of the variable resistance circuit 12 necessary to make the line loss equal to or greater than the system design upper limit value, by the gain control voltage. The control voltage is input to the control voltage terminal 104.

Figure 2 shows an example of a circuit configuration that generates this control voltage.

FIG. For example, the terminal 105 has the gain control voltage of the automatic gain control amplifier on the receiving side (this is used as a reference because it is known) at line loss exceeding the upper limit of this transmission system design mentioned above, and the terminal 106 has the gain control voltage for this test. A voltage is applied, and the comparison/drive circuit 15 generates a control voltage to be applied to the control voltage terminal 104. Currently, the line exceeds the upper limit value for this transmission method design.

The line loss of the transmission line to be tested is (dB), and the peak value of the transmission pulse signal during normal use (from output terminal 101 to
102) The standard value is E (V), and the voltage drop value to be lowered during the test is ■. (V) (converted between output terminals 101 and 102), decrease the value ■ so that it becomes . All you have to do is control the value of .

In the above embodiment, a case has been described in which a single test transmission pulse signal in which the height of the pulse peak value of the transmission pulse signal is lowered to a predetermined value is used to detect the code error rate in the transmission line. In this case, as mentioned above, the code error rate during normal use is estimated using the line loss versus code error rate characteristic curve obtained from the same type of equipment, lines, etc., which has been measured in advance, and the - number of tests is performed. It is possible to obtain almost accurate values.

However, as shown in FIG. 4, there are variations in the line loss of the transmission line under test, and it can be said that the values obtained in the tests of the above embodiments are correct within the range of this variation.

Therefore, in the second aspect of the present invention, the characteristic curve shown in FIG. 4 is obtained for the transmission line under test in consideration of this variation, and the code error rate during normal use is estimated from it.

That is, the code error rate is tested using at least two test transmission pulse signals having different pulse height reduction values, and the code error rate in normal use is estimated from the obtained values. In this case, instead of the characteristic curve in FIG. 4, a characteristic curve is obtained as the relationship between the decrease value of the pulse peak value and the bit error rate, and the value at the point where the decrease value is zero is estimated. A more accurate bit error rate for the test transmission line can be obtained.

Note that the estimation operation in the above embodiment can be automatically performed by a microprocessor.

〔Effect of the invention〕

As explained above, the present invention provides a method for testing transmission lines.
By lowering the pulse height value of the transmitted pulse signal by a predetermined value below the normal standard value, it is possible to quickly and accurately test subscriber transmission lines when characteristic deterioration occurs only stochastically. It is effective.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a main part of a transmission pulse signal output circuit according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a circuit that generates the control voltage. FIG. 3 is an explanatory diagram of a transmission pulse signal. FIG. 4 is a characteristic diagram showing the relationship between line loss and code error rate of a transmission line. FIG. 5 is a characteristic diagram showing the relationship between line loss of a transmission line and code error occurrence time. FIG. 6 (al, (bl) is a block diagram showing the configuration of a digital subscriber system transmission line to which an embodiment of the present invention and a conventional example are applied. 1... In-house equipment, 2... Line termination device, 3... Subscriber line, 4... Terminal device, 5... Subscriber line test circuit, 6... Signal transmitter, 7... Code error detector, 1
1... Output 1-lance, 12... Variable resistance circuit, 1
3... Switch, 14... Drive element system, 15...
Comparison/drive circuit, 101.102... Output terminal, 10
3...Pulse voltage input terminal, 104...Control voltage terminal, 105.106...Terminal, E...Specified value of peak value of transmission pulse signal during normal use, V,...During test Decrease value of pulse peak value of transmission pulse signal. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] (1) The transmission characteristics of a digital subscriber system transmission line including a line termination device and an end station device connected via a subscriber line are tested by transmitting a transmission pulse signal sent from the end station device to the line termination device. In a subscriber transmission line test method in which the test is performed by detecting the code error rate of the aliased signal using a device, during the test, the pulse height value of the above-mentioned transmission pulse signal is determined according to the normal standard specified for the above-mentioned digital subscriber transmission line. A subscriber transmission line testing method characterized by lowering the value by a predetermined value. (2) The decrease value V_0 (V) of the pulse peak value of the transmission pulse signal during the test is calculated using the following formula: 20log(E/[E-V_0])+L_a=L_m_
a_x However, E: Standard value of the pulse height value of the transmission pulse signal during normal use (V), L_a: Transmission line line loss (dB) of the test object, L_
m_a_x: line loss (dB) greater than or equal to the design upper limit value of the transmission line line loss to be tested; (3) The transmission characteristics of a digital subscriber system transmission line including a line termination device and an end station device connected via a subscriber line are tested by transmitting a transmission pulse signal sent from the end station device to the line termination device. In the subscriber transmission line test method, which tests by detecting the code error rate of the loop back using equipment, the pulse height value of the above-mentioned transmission pulse signal is set to the normal standard specified for the above-mentioned digital subscriber transmission line during the test. 1. A subscriber system transmission line testing method, characterized in that the code error rate is tested using the transmission pulse signals having at least two different reduction values.