JPH07105779B2 - Code error measurement method for optical digital transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the invention [Industrial field of application] The present invention relates to an optical digital device in which a plurality of optical digital repeaters (hereinafter abbreviated as "repeaters") are inserted in an optical fiber cable. The present invention relates to a code error measuring method of an optical digital transmission line for measuring a code error of each repeater in a transmission line in an in-service state.

[Prior Art] An optical digital system composed of a low-loss optical fiber and a repeater is required to have high reliability for a long period of time. Above all, an operating state of a repeater having a plurality of circuit elements is monitored and a failure occurs. In order to locate the fault location at the time of occurrence, it is important to measure and isolate code errors that occur in each relay section.

The conventional repeater monitoring method includes an out-service method of interrupting communication service and sending a special signal for measurement, and an in-service method of measuring a communication signal by superimposing a special signal on the transmission signal. is there. In the following description, an in-service method that can monitor the code error of each relay without interrupting the communication service will be described.

FIG. 4 is a circuit diagram of a conventional optical repeater R inserted in the upstream / downstream optical digital transmission lines F1 and F2. 1,1 ′ in the figure
Is an O / E conversion circuit that converts an optical signal into an electrical signal, 2, 2'is an E / O conversion circuit that converts an electrical signal into an optical signal, and 3, 3'is a regenerative repeater circuit that regenerates a digital pulse signal. Indicates. Four
Is a code error measuring unit for performing in-service code error measurement, and is composed of an instruction receiving circuit 5, an error counting circuit 6, and a response signal generating circuit 7.

FIG. 5 shows the structure of a conventional control command signal S1 sent from the landing station to the repeater R. In the figure, the command A is composed of a command word B indicating the content of the command to be executed by the repeater R and a response signal carrier C for returning the response signal S2. There are conventionally three types of instructions in the instruction word B used for in-service code error. The first instruction is an error measurement start instruction, the second instruction is a stop instruction, and the third instruction is an error measurement result response instruction. Instruct each. The repeater R that executes the command operation is specified by the repeater specifying code included in each command word B. A response signal carrier C for transmitting the response signal S2 is added to each command word B. Generally, the control command signal S1 is
The parity bit included in the transmission signal is even-odd-inverted at regular intervals and is transmitted by the carrier generated by the frequency division by the repeater R. On the other hand, the response signal S2 transmits the result from each repeater R to the landing station, and the measurement result is that the phase of the signal of the downstream or upstream optical digital transmission line F2, F1 is modulated at a low frequency to force so-called jitter. Is transmitted by being generated.

The response signal carrier C is a low frequency carrier for causing this jitter. Since the response signal S2 is transmitted as a binary digital signal, the response signal carrier C
Are burst-shaped, the number of which corresponds to the number of bits of the response signal S2.

FIG. 6 shows a conventional error measurement procedure using the control command signal S1. The first instruction A1 causes all the repeaters R to start measuring the error at the same time, and the second instruction A2 causes all the repeaters R to stop the measurement at the same time. Then, in accordance with the third instruction A3, the error count circuit 6 is sequentially provided from each repeater R.
The contents of the above are read out by the burst-like response signal carrier C, whereby the transmission signal of the downstream optical digital transmission line F2 is phase-modulated and the measurement result is transmitted as shown in FIG.

Considering the phenomenon of code error occurrence, there are cases in which the intervals at which errors occur are long in time, and cases in which errors frequently occur in a short time. First, when the occurrence of code errors is burst-like as in the former case, for example, the error count is measured over a long period (a period T in FIG. 6) of about one month, and the interval and time at which the errors occur. Investigating dynamic fluctuations.

On the other hand, in the latter case, the number of errors in a short time is measured,
Check the bit error rate. However, in the conventional error measurement system, the error is measured during the time T from the reception of the first command A1 to the reception of the second command A2, but if the frequency of the error is high, the error count circuit 6 may overflow. Therefore, it is necessary to make the time T sufficiently small or make the number of digits of the error count circuit 6 sufficiently large. For example, when the error counter circuit 6 is composed of 9 bits, if the code error rate of the optical digital transmission lines F1 and F2 is 10 ⁻⁴ , overflow occurs in 8 milliseconds.

However, the command receiving circuit 5 of the repeater R includes various time constant circuits in order to prevent malfunction due to various disturbance signals.

Therefore, after receiving the control command signal S1, the timing of starting the error measurement is slightly different for each repeater R, and the exact starting time cannot be known at the landing station. For this reason, the conventional second instruction A2 must be transmitted at an interval of about 500 milliseconds after the first instruction A1 is transmitted, and the probability of overflow of the error count circuit 6 is increased, and the high precision code is generated. There was a problem that the error measurement could not be performed.

[Problems to be Solved by the Invention] The present invention has been made in order to solve the above-mentioned problems of the prior art, and an optical digital transmission line capable of highly accurate measurement even if errors frequently occur. It is intended to provide a code error measurement method of.

(2) Configuration of the Invention [Means for Solving the Problems] A code error measuring method for an optical digital transmission line according to the present invention is a pulse signal which is successively transmitted following a control command signal for instructing error measurement, or Error measurement is started at the rise of the pulse signal of the arbitrarily set pulse signal created in the repeater, and error measurement is performed when the number of pulses reaches a predetermined number or the number instructed by the control command signal. Will be completed.

[Examples] Examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of the command A'in the control command signal S1 'used in the present invention, which is composed of at least a command B1 for instructing the start of error measurement and a command B2 for instructing the stop of error measurement. It consists of a response signal carrier C of clock pulses C1 to Cn for returning the error measurement result after the command word B '.

The response signal carrier C does not necessarily have to be sent from the landing station in advance, and may be created in the repeater R. In the following description, the case where the response signal carrier C is sent from the landing station will be described as an example. In order to simplify the explanation, the case where the measurement is started at the first rise of the clock pulse C1 of the response signal carrier C will be described as an example. However, the m-th clock pulse Cm (m is an integer of 1 or more) set arbitrarily You can start from.

Therefore, the error measurement is performed by the response signal carrier C which is continuously transmitted based on the content of the command word B1 after receiving the command word B '.
Starting at the first rising edge of the clock pulse C1 and stopping when the number of clock pulses of the response signal carrier C designated by the command word B2 or predetermined is received. The length of one clock pulse C1 to Cn (burst length) in the response signal carrier C is about 10 milliseconds, and since the response signal carrier C is created at the landing station, the clock pulse length and its repeated clock period are repeated. Since the clock pulse is extremely accurate in the embodiment of the present invention, the clock pulse is adopted as the response signal carrier C, but it is needless to say that other pulses that can form a burst-like response signal can be applied. Therefore, in the repeater R, an extremely short time measurement and an error measurement at an accurate time t are possible.

FIG. 2 is a circuit configuration diagram of the code error measuring unit 8 according to the present invention. In the figure, 9 is a command receiving circuit, 10 is a response signal carrier receiving circuit, 11 is a counter, 12 is a gate circuit, 13 is an error counting circuit, 14 is an error detecting circuit, and 15 is a response signal creating circuit.

Therefore, when the instruction receiving circuit 9 receives the instruction A ', it outputs a gate open control signal to the gate circuit 12 so that the error can be counted. On the other hand, the response signal carrier C received by the response signal carrier receiving circuit 10 is guided to the counter 11, and the counter 11 opens the gate circuit 12 by the first response signal carrier C1 and counts the preset number of clock pulses. Then, the gate circuit 12 is closed.

This enables the measurement shown in FIG. The number of errors measured by the error count circuit 13 is read by sending the third instruction A3, and the response signal generation circuit is read.
The response signal S2 created in 15 can be superposed on the response signal carrier C and returned to the landing station via the downstream optical digital transmission line F2.

In the present invention, it is naturally possible to use the first instruction A1 and the second instruction A2 together. First instruction A1 and second instruction A2
By using, it is possible to measure error at any time and cope with burst-like error occurrence.

FIG. 3 shows the experimental results of the present invention. In the figure, the bit rate is about 600 megabits, the horizontal axis represents the code error rate of the optical digital transmission lines F1 and F2, and the vertical axis represents the error count number. X is the case where the error measurement of 10 milliseconds is executed by the instruction A'using the code error measuring method according to the present invention, and Y is the first instruction A1 and the second instruction A2 which are the conventional code error measuring methods. It is an experimental result when the measurement for 500 milliseconds was performed using.

As is clear from the figure, the present invention enables error measurement for a short time t, and therefore, error counter circuit 13 can be measured without overflow. The code error rate is two orders of magnitude lower than that of conventional measurement methods, and can be up to about 10 ^-4 .

Thus, although the present invention has been described with reference to the above embodiment, it is clear that the instruction A'need not be included if the information specifying the error measurement time is fixed. Besides the above description, the present invention can be applied to the case where the response signal carrier C is created inside the repeater R instead of being transmitted from the landing station.

Further, in the above description, the clock pulse length of the response signal carrier C is 10 milliseconds, but the clock pulse length of the response signal carrier C or the clock pulse length of the pulse signal created in the repeater R is changed. Can obtain an arbitrary measurement time.

(3) Effects of the Invention Thus, according to the present invention, since the start and stop of error measurement are measured by using the pulse of the pulse signal generated in the response signal carrier C or the repeater R, errors frequently occur and bursts occur. The effect is great such that the error can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of control command signal contents used in the present invention, FIG. 2 is a block diagram showing a circuit configuration of a code error measuring unit for implementing the present invention, and FIG. 3 is an error measurement between the present invention and a conventional example. FIG. 4 is a block diagram showing a circuit configuration of a repeater including a conventional in-service code error measurement unit, FIG. 5 is a configuration diagram of control command signal contents used in a conventional measurement method, and FIG. FIG. 7 is a diagram illustrating a conventional procedure for measuring an error using a control command signal. A, A '... Command, A1 ... First command A2 ... Second command, A3 ... Third command B, B' ... Command word, C ... Response signal carrier C1, C2, C3 , Cn …… Clock pulse F1 …… Upstream optical digital transmission line F2 …… Downstream optical digital transmission line R …… Optical repeater, S1 …… Control command signal S2 …… Response signal 1,1 ′ …… O / E conversion Circuit 2, 2 '... E / O conversion circuit 3, 3' ... Regenerative repeater circuit 4, 8 ...... Code error measuring unit 5, 9 ...... Command receiving circuit 6, 13 ...... Error count circuit 7, 15 ... … Response signal creation circuit 10 …… Response signal carrier reception circuit 11 …… Counter, 12 …… Gate circuit 14 …… Error detection circuit

Claims (1)

[Claims] 1. In an optical digital relay system having a command receiving circuit and a transmission signal error counting means in a repeater, a control command signal transmitted in service for instructing the start of the error counting is followed by an in service. By transmitting a pulse signal or creating a pulse signal in the repeater,
The error measurement is started by receiving the arbitrarily set number of pulses of the pulse signal, the number of pulses is counted in the repeater, and the number of pulses determined in advance or the number of pulses instructed by the control command signal is counted. Code error measurement method for optical digital transmission line characterized by continuing error measurement until completion