JPS6022856B2 - Fault monitoring method for relay transmission lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fault monitoring method for a relay transmission line, and in particular, the present invention relates to a fault monitoring system for a relay transmission line, and in particular, a relay transmission line that uses a digital transmission system and is configured by alternately arranging transmission media and intermediate repeaters, The present invention relates to a method for monitoring intermediate repeaters and laser diodes and searching for faults.

When transmitting a telephone signal using a digital transmission method with a high degree of multiplexing, it is converted into a digital signal by a PCM-24 terminal equipment, and the multiplexed signal is further time-division multiplexed by a multiplex converter and transmitted. .

Further, television signals and data signals are encoded into digital signals by dedicated terminal equipment, and then time-division multiplexed by a multiplex converter and transmitted. Digital systems using coaxial cables include PCM-100M system and PCM-100M system.
There are CM-400M systems, etc., and the former is used to create toll lines from central stations to general stations, and the latter from central stations and above. FIG. 1 is a block diagram of a fault search circuit used in the subordinate coaxial PCM-400M system. In the relay transmission path, transmission media and intermediate repeaters 8 are arranged alternately, and in the intermediate repeater 8 shown by the broken line, an equalization circuit 1, an identification regeneration circuit 2, a T-type flip-flop 3, and a low-pass A monkey wave device 4 and a transformer 5 are incorporated.

Further, a bandpass waveform generator 6 and an intervening pair 7 are connected. Conventionally, as a monitoring/fault detection method for such digital transmission lines, a pseudo-random signal is mark rate modulated with a low frequency signal, and then a fault detection signal is created by performing logical multiplication on this signal, and the fault detection signal is detected offline. This fault search signal is sent from the station, and the input signal a from the transmission line is sent to each intermediate repeater 8.
Add to.

This fault search signal is subjected to waveform equalization in the equalization circuit 1, and its output is guided to the output of an intermediate repeater 8 (not shown in FIG. 1), and is sent out to the next intermediate repeater. . On the other hand, the output of the identification reproducing circuit 2 is branched to T
The signal is guided to a type flip-flop 3, a transformer 4, and a bandpass filter 5, in which unique low frequency components are detected and transferred to the terminal station using an intervening pair 7 or the like. In this method, the error rate of the intermediate repeater 8 can be measured by counting the phase inversion of the low frequency signal when a code error occurs in the intermediate repeater 8. FIG. 2 is a diagram showing the fault search signal used in FIG. 1.

As shown in FIG. 2, the fault search signal is composed of a pseudo-random signal, and the frequency fo (=1/To ) modulates its mark rate with a low frequency signal.

When searching for a fault, the fault searching signal shown in Figure 2 is sent to the offline transmission line, but in this case, the fault searching signal is subjected to logical multiplication, and the transmitted signal is After passing through the equalization circuit 1 and the identification reproducing circuit 2, T
Since the T-type flip-flop 3 performs logical division, which is the inverse operation of the logical multiplication performed on the transmitting side, the signal shown in FIG. 2 is reproduced at the output of the T-type flip-flop 3.

In the signal of FIG. 2, the DC level in a portion A with a high mark rate is high, while the DC level in a portion B with a low mark rate is low. The magnitude of this DC level is determined by a constant period To
, that is, it is repeated at a repetition frequency fo (=1/To), so when the signal shown in FIG. 2 is passed through the low-pass filter 4 whose cut-off frequency is higher than fo, its low frequency components can be extracted. I can do it. This low frequency component fo is transferred to the terminal station via the transformer 5, Obijo pass-through transducer 6, and intervening pair 7. The frequency fo used to modulate the fault search signal is determined separately for each intermediate repeater 8, and the center frequencies of the belt wavers 6 in each intermediate repeater 8 are made to coincide with each other. ing.

Therefore, by sending out a fault search signal with a specific modulation frequency fo from the terminal station, it becomes possible to specify the intermediate repeater 8 whose error rate is to be detected at the terminal station. now,
If the number of marks of the pseudorandom signal used as a fault search signal is an even number, the transmission line and intermediate repeater 8
When a code error does not occur in L, the output state of the T-type flip-flop 3 returns to the original state each time the fault search signal is repeated. However, if a code error occurs in a certain bit, the output state of the T-type flip-flop 3 returns to the original state every time the fault search signal is repeated. The output state of the flop 3 is inverted, and as a result, the phase of the low frequency component at the output of the low-pass waveform generator 4 is inverted.

By counting this phase reversal at the terminal station, the error rate of the intermediate repeater can be measured.

The above-mentioned monitoring/fault detection method is generally called a phase detection fault detection method, and its principle is based on the IEICE Journal, 59 Lid No. 11, 1970 Matsushita, JIl Island r Code Errors in Digital Transmission Lines. Rate telemetry is described in detail in J.

However, when the above-mentioned phase detection type fault search method is used alone, the fault location accuracy is in units of one relay section, so it is not possible to completely distinguish whether the fault location is a transmission line or an intermediate repeater.

In addition, when transmitting a fault search signal to a relay transmission line using an optical fiber cable, the intermediate repeater converts the optical pulse train into an electrical signal, performs identification and regeneration, and then converts it back into an optical pulse train to transmit the signal to the optical fiber cable. Since it is sent to the cable, the output of the identification and regeneration circuit is branched and used, but in this case, the laser diode driven by the output of the identification and regeneration circuit is monitored only by using the above fault search signal. That is impossible. An object of the present invention is to eliminate these conventional drawbacks by making it possible to separate failures in the transmission medium, intermediate repeaters, and zazer diodes within one relay section of a digital transmission line, thereby reducing maintenance costs. An object of the present invention is to provide a fault monitoring method for a relay transmission line that is simple and can maintain compatibility of intermediate repeaters.

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

FIG. 3 is a block diagram of a fault search circuit of an intermediate repeater showing an embodiment of the present invention, and FIG. 4 is a diagram showing an example of a fault search signal pattern used in FIG. 3.

In FIG. 3, the same reference numerals as in FIG. 1 indicate the same parts.

In addition to the configuration shown in FIG. 1, FIG.
A diode 12, an abnormality detection circuit 13, and a square wave oscillator 14 are newly provided. The light receiving element 9 converts the optical signal input to the intermediate repeater 8 into an electrical signal, and converts the optical signal input into the intermediate repeater 8 into an electrical signal.
lead to. Next, in the present invention, the intermediate repeater 1 shown in FIG.
In order to detect the interruption of the input signal to 8, a fault detection signal pattern as shown in FIG. 4a is used.

Normally, in the digital optical fiber transmission system, the transmission waveform is a pulse with a 50% occupancy rate as shown in Figure 4b.
The R2 skin shape is used.

As shown in Fig. 4a, in the fault search signal, the data length of the portion C with a large mark rate and the portion D with a small mark rate are equal (T in units of time), and the number of data pieces is 21. .

The number of marks in each part C and D is set so that part C is 2h and part D is small (m, n: integer) and the condition IZm>n is satisfied.Also, the position of the mark is ,
The intervals between the marks are set to be equal when part C or D is sent out alone. As a result, a portion C with a high mark rate and a portion D with a low mark rate are repeated at a constant period t (=2.T,), and the pulse density is a low frequency signal with a frequency fo (=1 no To). A modulated fault finding signal pattern is obtained.

FIG. 4b shows an example of this fault search signal pattern.
The case where 1=m=4, n=1 is shown. The reason for configuring the fault search pattern in this way is to ensure that when the fault search pattern is passed through a 1/2 frequency divider circuit, the DC level of the output signal will be constant, as will be described later. In Fig. 3, when monitoring input signal interruption to the intermediate repeater 18, the fault search signal pattern shown in Fig. 4a is sent from the terminal station to the off-line transmission line without performing logical multiplication. do. If there is no disconnection in the transmission line,
The transmitted signal pattern shown in FIG. The fundamental wave component of is extracted. The frequency of this low-frequency signal is fo, and after being amplified to a sufficient amplitude by the amplifier circuit 11, it is transferred to the terminal station via the transformer 5, the band waver 6, and the intervening pair 7, and then to the repeater 18. It is possible to detect that there are no abnormalities such as disconnections in the transmission line. On the other hand, repeater 1
If there is an abnormality such as a disconnection in the transmission path to the input terminal of 8 or the intermediate repeater, the low frequency signal will not be transferred to the terminal station along the above-mentioned path, so the transmission in the section between the general station and the input of repeater 18 will be interrupted. road abnormalities can be detected. next,
The interference signal along the path of the light receiving element 9, the equalization circuit 1, the identification/reproduction circuit 2, the T flip-flop 3, and the low-pass waveform filter 4 will be explained.

The fault search pattern shown in Figure 4 sent to the transmission path is as follows:
Unlike the case in Figure 1, no logical multiplication is performed, so if no code error occurs, a signal exactly the same as the signal shown in Figure 4 is reproduced at the output of the identification and reproduction circuit 2. . As mentioned above, in the digital optical fiber transmission system, since an RZ waveform with a pulse occupancy rate of 50% is used, the signal inputted from the light receiving element 9 to the identification reproducing circuit 2 via the equalization circuit 1 also has an output corresponding to the RZ waveform. This results in an isolated waveform.

Therefore, when the fault search pattern is input to the T-type flip-flop 3 via the equalization circuit 1 and the identification/reproduction circuit 2, the frequency is divided by 1'2 by the T-type flip-flop 3.

FIG. 5 is a waveform diagram in which the signal pattern of FIG. 4 is frequency-divided by 1/2 by a flip-flop.

The fault search signal pattern shown in FIG. 4b is frequency-divided by 1/2 by the T-type flip-flop 3 to become as shown in FIG. In the waveform shown in Fig. 5, the DC level of the part corresponding to the part C with a high mark rate in Fig. 4 is equal to the DC level of the part corresponding to the part D with a low mark rate in Fig. 4. The output obtained by passing the waveform shown in FIG. 5 through the low-pass filter 4 no longer contains low frequency components. This means that for a signal sent along the path of the light receiving element 9, the low frequency component extraction circuit 10, and the amplifier circuit 11, that is, a signal for detecting the presence or absence of an input signal to the intermediate repeater, the light receiving element 9 From equalization circuit 1, identification reproduction circuit 2
, the T flip-flop 3, and the low-pass waver 4. Note that it is also possible to set the modulation frequency of the fault search signal pattern to f, which is different from fo, but in this case, a dedicated band waver and an intervening pair are required. At the terminal station, the presence or absence of the input signal at each intermediate repeater can be monitored by detecting the presence or absence of the low frequency signal assigned to each intermediate repeater transferred by the above method. It is possible to detect whether there is an abnormality such as a disconnection in the transmission line or intermediate repeater in the section from the terminal station to the input end of the repeater. Therefore, by repeating this sequentially, the abnormal section can be
(Intermediate repeater) It is possible to locate in units of 10 (transmission line) J. On the other hand, in the conventional phase detection fault detection method, fault sections can be located in units of 10 (transmission lines) (intermediate repeaters). It becomes possible to distinguish whether the fault is a fault or a fault in an intermediate repeater. Next, in FIG. 3, when measuring the error rate of the digital transmission path consisting of the intermediate repeater 18 and the transmission medium, when a fault occurs, the fault search signal shown in FIG. After performing logical multiplication, if it is sent from the terminal station to the offline transmission line, the intermediate repeater 18
The error rate can be measured.

In this case, the spectrum of the signal component after performing logical multiplication on the fault search signal does not include any low frequency components, or
Alternatively, even if such a fault detection signal is included, it is necessary to select a fault search signal that falls within a band in which the low frequency component is sufficiently suppressed by the path between the low frequency component extraction circuit 10 and the amplifier circuit 11. In this way, the influence of the low-frequency signal component appearing on the output of the low-pass monkey waver 4 due to the path of the light receiving element 9, the low-frequency component extraction circuit 10, and the amplifier circuit 11 can be reduced.
Can be completely ignored.

Next, the case of monitoring the laser diode 12 will be explained with reference to FIG.

The laser diode 12 in the optical repeater is driven by the output of the identification reproducing circuit 2, and if an abnormality occurs in its output power, an abnormality detection circuit 13 detects it.

That is, the laser diode abnormality detection circuit 13 branches, for example, a part of the forward light coupled to the optical fiber out of the optical output of the laser diode 12, monitors the output power, and outputs a predetermined output power. If it is out of the range, an abnormality detection signal is output. Alternatively, it is also possible to use a portion of the backward light of the optical output of the laser diode 12. Furthermore, it is generally known that as a laser diode deteriorates, its threshold current increases. In addition, the threshold current has temperature dependence, so in order to stabilize the output power of the laser diode, an automatic control circuit that varies the DC bias current flowing through the laser diode is usually used. There is. As described above, the DC bias current of the laser diode may be monitored and compared with a predetermined range, and if it deviates from the range, an abnormality detection signal may be output. However, it is necessary to perform temperature correction on one of the two to be compared. When an abnormality detection signal is output,
An extremely low frequency rectangular wave oscillator 14 operates. The output of the square wave oscillator 14 is connected to the reset terminal of the T-type flip-flop 3.
The output of the T-type flip-flop 3 is converted as shown in FIG. 6. In FIG. 6, a portion E includes several to several parts of the portion A with a large mark rate and the portion B with a small mark rate in FIG. Note that the period T is TIlt
satisfy. The output of the T-type flip-flop 3 is a low frequency waveform generator 4, a transformer 5, a bandpass waveform 6, and an intervening pair 7.
The data is transferred to the terminal station via .

In this case, it is necessary to set the oscillation frequency of the rectangular wave oscillator 14 to be smaller than 1/2 of the pass band width of the band wave generator 6. Abnormalities in the laser diode 12 can be determined by monitoring the signal transferred from the intermediate repeater 18 to the terminal station when the fault search signal shown in FIG. 2 is sent out in order to measure the error rate of the relay transmission line. Can be detected.

In other words, when measuring the error rate of a relay transmission path, if the low frequency signal detected at the terminal station is modulated by an extremely low frequency signal lower than that frequency, the intermediate relay performing the fault search Laser diode 12 of device 18
can detect that there is an abnormality. In addition, the square wave oscillator 1
4 as a voltage controlled oscillator (VCO), it is possible to obtain multiple information (different types of faults).

As explained above, according to the present invention, a function for determining the presence or absence of an input signal to an intermediate repeater and a function for detecting an abnormality in a laser diode are added to the conventional phase detection fault detection method. , transmission medium failure within one relay section, intermediate repeater failure, and laser.

Diode failures can be clearly isolated, making maintenance extremely easy. In addition, since the newly added fault monitoring circuits in the intermediate repeaters can all have the same configuration, the compatibility of the intermediate repeaters is maintained, the manufacturing process is easier to manage, and there are fewer spare repeaters to keep. Teyo・〈
, which is extremely useful for maintenance and operation.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a fault detection circuit in a conventional intermediate repeater, Fig. 2 is a diagram showing a fault detection signal used in Fig. 1, and Fig. 3 is a diagram of an intermediate repeater showing an embodiment of the present invention. A block diagram of the fault search circuit, FIG. 4 is a diagram showing an example of the fault search (detection of disconnection of input signal to the intermediate repeater) signal pattern used in FIG. 3, and FIG. 5 is a diagram showing the signal pattern of FIG. 4. 1
FIG. 6 is a waveform diagram when the fault search signal of FIG. 2 is modulated when the laser diode is abnormal. 1...Equalization circuit, 2...Identification reproducing circuit, 3
...T type flip flop, 4...
・・・Reduced passing wave device, 5... Transt 6・
...Bandpass filter, 7...Intervening pair, 8,18.
... Intermediate repeater, 9... Light receiving element, 10...
...Low frequency component extraction circuit, 11...Amplification circuit,
12... Laser diode, 13... Abnormality detection circuit, 14... Square wave oscillator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. Transmission media and intermediate repeaters are alternately connected between both end stations, and the mark rate is modulated in the intermediate repeaters by a first low frequency signal assigned to each intermediate repeater. The circuit is equipped with a circuit that measures the error rate by generating a second low-frequency signal whose phase is inverted every time an error bit occurs, when receiving a fault search signal obtained by further performing logical multiplication on the pseudorandom signal obtained by In the relay transmission line of the digital transmission system, a fault search pattern whose pulse density is modulated by a third low frequency signal having the same frequency as the first low frequency signal is received, and a third low frequency signal is detected from the fault search pattern. a low frequency component extraction circuit for extracting a fourth low frequency signal having a frequency equal to the low frequency signal of the low frequency signal, a circuit for amplifying the output of the low frequency component extraction circuit, and means for coupling the output of the amplification circuit to an intervening pair. A failure monitoring system for a relay transmission line, characterized in that a terminal station monitors an input signal disconnection of an intermediate repeater based on the presence or absence of the fourth low frequency signal transferred via the intervening pair. 2 Transmission media and intermediate repeaters are alternately connected between both end stations, and the intermediate repeaters receive a pseudo-random signal whose mark rate is modulated by a first low frequency signal assigned to each intermediate repeater. , a digital transmission system equipped with a circuit that measures the error rate by generating a second low-frequency signal whose phase is inverted every time an error bit occurs when receiving a fault search signal that has been further subjected to logical multiplication. A fault search pattern whose pulse density is modulated by a third low frequency signal having a frequency equal to that of the first low frequency signal is received in the relay transmission path, and from the fault search pattern, a signal equal to the third low frequency signal is received. a low frequency component extraction circuit for extracting a fourth low frequency signal of the frequency, means for coupling the output of the low frequency component extraction circuit to an intervening pair, means for detecting an abnormality in the laser diode, and activation by the output of the abnormality detection means; a rectangular wave oscillator, and means for logically multiplying the output of the rectangular wave oscillator and the second low frequency signal, wherein the second low frequency signal is on-off modulated with an even lower low frequency signal. A failure monitoring method for a relay transmission line, characterized in that an abnormality in a laser diode is monitored at a terminal station depending on whether or not the laser diode is being operated.