JPH0378021B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a monitoring system for optical digital transmission lines, and more particularly to a monitoring system for optical repeaters using an in-service method that does not require intervening pairs.

(Background technology) In digital transmission lines that include repeaters, it is important to isolate and measure code errors that occur in each repeater section in order to monitor the operating status of repeaters and locate the fault location when a fault occurs. It is.

Conventionally, methods for isolating and measuring code errors include the out-of-service method, in which the service is interrupted and a special signal is sent for measurement, and the in-service method, in which the special signal is superimposed on the transmitted signal while the service is in progress. be.

A common form of out-of-service method is to provide a return line between the upstream and downstream transmission lines within the repeater, and control this line from the terminal station to loop back the sent test signal. This method includes
Although it has the disadvantage of having to interrupt the service, it does not require a separate line such as an intervening pair to send the test signal from the repeater back to the end station, so it is similar to the long-distance optical submarine cable method.
Suitable for systems where the use of intervening pairs is inappropriate.

On the other hand, as an in-service method, a method is widely known in which the parity bit of the transmission signal is manipulated and code error information detected in the repeater is transmitted to the terminal station through an intervening pair (for example, CCITT contribution COM
No. 59-E August 1977). However, this method has the drawback of requiring repeaters to compensate for transmission loss in the intervening pairs when it comes to long-distance systems, making the system large-scale, making it impractical in terms of economy and reliability. Not.

Here, among these conventional techniques, the in-service method that is closely related to the present invention will be described, in particular, its signal processing.

Figure 1 shows the signal waveform. Figure 1a shows the signals sent to the transmission line, 11, 12, 13, 1
4, 15 are signal blocks, 21, 22, 23, 2
4 and 25 are parity bits. Assume that this parity bit is inserted according to the even parity rule. That is, if the number of marks ("1") in block 11 is even, the parity bit 21 is "0"; if the number is odd, the parity bit is controlled to "1"; , the number of marks in block 11 is always an even number.
Therefore, even if the signal of a is divided in half by a flip-flop, the parity bits 21,
The outputs of the flip-flops at the positions corresponding to 22, 23, 24, . . . are always constant. FIG. 1b shows the output signal of a flip-flop. 3 is the frequency-divided signal of block 11, which is “1”, “0”
occurs randomly. 4 is parity bit 21
It is assumed that it is located at a position corresponding to , and is "1". Now, if an error occurs in the bit at position 5 of the signal a, the number of marks including the parity bit 23 of block 13 will be an odd number, so the flip-flop will be inserted at position 41 corresponding to the parity bit 23. Output is inverted and becomes “0”
becomes. Thereafter, if there is no error in block 14, the polarity of the output of the flip-flop remains at "0" at position 42 without any change. Thus, when a bit error occurs and the even parity law is violated, the output of the flip-flop is inverted. This also applies when the parity bit is intentionally inverted.

FIG. 1c shows the DC component of the signal b obtained using a low-pass filter. As is clear from c, a change occurs in the DC potential at the point corresponding to the bit error. Therefore, by sending the change in DC potential back to the terminal station via an intervening pair or the like, it is possible to detect the occurrence of a code error on the transmission line.

The above is the principle of code error detection in the prior art.

By the way, in a digital transmission line in which a large number of repeaters are inserted, it is necessary to specify (identify) the repeaters. A conventional example of this technique will also be described.

As shown in FIG. 2, the output of the flip-flop 8 is connected to an intervening pair 9 via a bandpass filter 10. Different low frequency center frequencies f _p are assigned to the bandpass filters 10 of each repeater. Then, as shown in FIG. 3a, from the terminal station, the bandpass filter 10 of the repeater to be monitored is
At a frequency double f _p , odd parity is inserted into the transmission signal and sent. In this way, a low frequency signal 6' of f _p can be obtained at the output of the flip-flop 8, as shown in FIG. 3b. If a code error occurs in 5, the number of marks in that block becomes an even number, and the potential of the flip-flop output does not change as shown at 7' in FIG. 3B. Therefore, by detecting the phase of the returned signal at the terminal station, it is possible to detect a code error at the repeater specified by the odd parity insertion period.

The conventional repeater monitoring method using the in-service method has been described above. As mentioned above, this conventional technology requires an intervening pair, so if it is applied to a long-distance system such as an optical submarine cable system, a repeater is also required for the intervening pair, which reduces economic efficiency and reliability. The disadvantage is that it is not practical in terms of gender. Additionally, the prior art has problems with power supply to the repeater. That is, the repeater inserted into the cable is inserted in series into the power supply path, and is supplied with constant current. This is to reduce the power supply current value. However, within a single repeater, multiple relay circuits, such as a relay circuit for uplink transmission lines and a relay circuit for downlink transmission lines, are connected in parallel and supplied with power, so the power supply current from the terminal station is transferred to one relay circuit. This is multiple times the current required by the circuit. This is not a big problem in a system where only two to three relay circuits are accommodated in one repeater, such as the conventional coaxial cable system. However, in systems such as the optical submarine cable system, a large number of optical fibers (for example, six) are accommodated within the cable, and the same number of repeater circuits as the number of optical fibers are accommodated within the repeater. So,
The power supply current value also increases, which poses a problem in system design. Therefore, as explained in FIGS. 1 and 2, a system that transfers DC components between multiple relay circuits or has DC coupling when viewed from the power supply is not suitable for accommodating a large number of relay circuits. Moreover, it is not a good idea to apply it to an optical submarine cable system that supplies constant current.

(Problems to be solved by the invention) The present invention solves the above-mentioned drawbacks of the prior art, and is an in-service monitoring system that does not require an intervening pair, and is suitable for an optical submarine cable system that performs constant current power supply. The purpose of this system is to provide a repeater monitoring system, and its feature is that by manipulating only the parity bit added to the transmission signal, a repeater identification signal and a test signal are constructed, and the signal is detected by the repeater. The information of the test signal is transmitted to the terminal station by subjecting the clock signal regenerated by the repeater to phase modulation.

(Structure and operation of the invention) FIG. 4 shows an embodiment of the invention. In the figure, 51 is a landing station, 52 is an optical transmission terminal station, 54 is an optical fiber for uplink transmission line, 63 is an optical fiber for downlink transmission line, 55, 55' is a monitoring circuit provided in the repeater, 56, 56' is a control command receiving circuit; 57;
57' is a flip-flop, 58, 58', 60,
60' is a gate circuit, 59 and 59' are phase modulation circuits, 61 is a capacitor, 64 is an oscillator, and 65 is an optical receiving terminal station. Note that the regenerative amplifier and the like necessary for the repeating operation of the repeater are omitted from the diagram.

Next, the operation of this embodiment will be described, but to make it more concrete, the following example will be used. However, the present invention is not limited to the numerical values in the examples.

The transmission signal sent from the optical transmission terminal station 52 to the optical fiber 54 has a communication speed of 291.2 Mbps, and the parity bit is 1 every 25 bits according to the even parity rule.
It is assumed that 1400 bits constitute one frame. In this example, an arbitrary
The parity bit that appears every 5600 bits (equivalent to 4 frames) will be manipulated.

Now, the optical transmission terminal station 52 inverts the polarity of all parity bits that appear every 5600 bits (assumes odd parity law) and sends out a transmission signal, and the transmission signal received by the control signal receiving circuit 56 of the repeater is If the frequency is divided by 1/2, a pulse train of 26 Kbps can be obtained as a frequency-divided output according to the principle explained in FIG.
This pulse train can be regarded as a binary code, so it is “1”,
Any combination of "0"s (binary code) can be configured. Therefore, the control command receiving circuit 56 includes a memory that stores a binary code uniquely assigned to the repeater, a flip-flop that divides the frequency of the transmission signal, a shift register that sequentially stores the output of the flip-flop, and a shift register that sequentially stores the output of the flip-flop. A matching circuit is provided to compare the contents of the register with the contents of the memory, and the optical transmission terminal 52 manipulates the parity bit of the transmission signal to correspond to the binary code of the repeater to be identified. If it is sent, "1" is obtained from the output of the matching circuit, and the repeater can be identified. This combination of parity bits for specifying a repeater is called a control command.

As described above, when the control command receiving circuit 56 receives a control command, the gate 58 is opened by the output signal of the control command receiving circuit 56.

Following the control command, the optical transmission terminal station 52 sends out a transmission signal in which all of the above-mentioned 5600 bits have odd parity. This part is called a test signal. If this test signal is frequency-divided by flip-flop 57, it will be 26KHz as mentioned above.
get the signal. This signal is guided to the modulation circuit 59' of the downstream transmission path monitoring circuit 55' via the gate 58 and capacitor 61, which are already open. The modulation circuit 59' converts the clock signal 62' extracted by a regenerative relay circuit (not shown) into a 26K
Modulate with Hz signal. That is, clock signal 6
2' is given a phase shift according to the output of the flip-flop 57. Therefore, the transmission signal propagating through the downlink optical fiber 63 becomes a signal whose pulse position shifts in accordance with the output of the flip-flop 57. However, this shift amount is given within a range that does not degrade the quality of the transmission signal. The optical receiving terminal station 65 can detect the above-mentioned signal component as phase jitter. This phase jitter is caused by the constant frequency oscillator 64 used to create the test signal.
The output and phase of are compared. If a bit error occurs on the upstream transmission path, the phase of the phase jitter will not change, so if a relative 180° phase change is detected, the bit error will be detected on the upstream transmission path 54 from the optical transmission terminal station to the repeater. It is possible to measure the code errors that occur in

Similarly, when measuring from a partner station (not shown) of the station 51, a test signal may be sent to the optical fiber 63 following the control command. At this time, the gate 58' is opened and the clock signal 62 on the upstream transmission line 54 is modulated by the output signal of the flip-flop 57'.

The basic operation of this embodiment has been explained above.
By the way, when a failure occurs in the regenerative relay circuit, etc., the bit error rate of the transmission path decreases, and the control command receiving circuit 5
It is conceivable that the control command cannot be detected in step 6. In this case, the basic operation described above becomes impossible. Gates 60 and 61' are provided to solve this drawback.

Next, this operation will be described.

FIG. 5 is a conceptual diagram of the measurement system. In the figure, A and B are terminal stations, 68 and 69 are repeaters, 70 is a control command, 71 is a test signal, and 72 is information.
FIG. 5a shows the basic operation described above, in which a control command and a test signal are sent from the terminal station A to the uplink transmission line fiber 54, and the information 72 detected by the repeater 68 is sent to the repeater 69. The signal is transmitted to the downlink transmission path 63 and returned to the terminal station A.

FIG. 5b shows a case where the condition of the uplink transmission line 54 is poor and the repeater 68 cannot identify the control command 70. In this case, only the control command 70' is sent from the terminal station B, the test signal 71 is sent from the terminal station A, and the code error on the uplink transmission path 54 is measured. However, in this case, the control instructions 70 and 70' include:
Assign binary codes that are different from each other.

In FIG. 4, gate 60' creates the measurement system of FIG. 5b. Control command receiving circuit 5
When 6' detects a control command 70' on the down transmission line 63, it opens the gate 60', and the test signal on the up transmission line 54 is transferred to the down transmission line 63 via the flip-flop 57-60'-modulation circuit 59' path. sent to.

Gate 60 was also provided for the same purpose,
This is used when the terminal station to be measured is B in FIG. 5b.

As described above, the control command receiving circuit 56
When the second control command 70 is received, the gate 58 is activated, and when the second control command 70' is received, the gate 60 is activated.
When the control command receiving circuit 56' receives the first control command 70, the gate 58' is configured to open.
The gate 60' is configured to open when the second control command 70' is received, thereby making it possible to perform any of the measurements shown in FIG. This is not only a measure against transmission path failure, but also a measure against control command receiving circuit 5.
6,56' and gate 58,58',60,6
This also provides redundancy for 0' and increases the reliability of the monitoring circuits 55, 55'.

Note that the capacitor 61 in FIG.
This is to provide direct current insulation between the The signal interface between the monitoring circuits 55 and 55' is:
Since it is only a low frequency signal, AC coupling by the capacitor 61 is possible, and DC insulation is realized.
As a result, the power supply systems of each circuit can be connected in series as described above, and in an optical digital relay system where the power supply current is large, the effect of reducing the power consumption of the system is significant.

As described above in detail, according to the present invention,
It has the following advantages, benefits and effects compared to the conventional technology.

(1) It is extremely economical because no intervening pair is required.

(2) There is no reduction in communication throughput.

(3) Phase modulation is used to return information from the repeater, so there is no deterioration in the quality of the transmitted signal.

(4) The signal configuration for measurement is divided into control commands and test signals, and control commands can be arbitrarily assigned binary codes for each repeater or function, and test signals are common to each repeater. Yes, and can be monitored under the same conditions.

(5) Inside the repeater, only the low-frequency signal components are extracted from the transmission signal, and code errors are detected at the terminal station, so the structure inside the repeater is simple.

(6) The redundancy of the monitoring circuit can be increased along with the diversity of the monitoring system.

As described above, according to the present invention, the economic efficiency and reliability of the system can be easily improved, and the effects on maintenance and operation are also extremely large.

Although an optical submarine cable system has been cited as an example, it is obvious that the present invention can be widely applied to digital communication systems in which transmission signals are blocked and have parity bits.

[Brief explanation of drawings]

Figure 1 is a diagram showing the signal waveform of the in-service method, Figure 2 is a block diagram of the discriminator, and Figure 3 is a diagram showing the signal waveform of the in-service method.
4 is a block diagram of an embodiment of the present invention, and FIG. 5 is a diagram showing the concept of a measurement system according to the present invention. 51; Landing station, 52; Optical transmission terminal station, 55, 5
5'; Monitoring circuit, 56, 56'; Control command receiving circuit, 57, 57'; Flip-flop, 58, 5
8', 60, 60'; gate circuit, 59, 59';
Phase modulation circuit, 61; capacitor, 64; oscillator, 65; optical receiving terminal station.

Claims (1)

[Scope of Claims] 1. In an optical repeater monitoring system for an optical digital transmission line consisting of an optical fiber for uplink and downlink transmission lines provided between two terminal stations and a repeater inserted into the optical fiber, the repeater a control command receiving circuit that identifies a code assigned in advance to the repeater corresponding to the upstream and downstream transmission paths; and a control command receiving circuit that frequency-divides the transmission signal transmitted on the transmission path to extract low frequency components. A flip-flop and a modulation circuit that gives a phase shift to the clock signal are provided, and from the terminal station, the parity bits included in the transmission signal are inverted even-odd, and a control command for identifying the repeater and a code error in the transmission path are sent. The repeater transmits a test signal for measurement and receives the control command, and converts the output signal of the flip-flop provided for one transmission line to the other transmission line according to the function specified by the control command. The terminal station extracts the low frequency component from the received transmission signal, and calculates the bit error rate at the identified repeater from the phase inversion information of the low frequency component. An optical repeater monitoring method characterized by in-service monitoring. 2. The optical repeater monitoring system according to claim 1, wherein the flip-flop and the modulation circuit are connected through a capacitor.