JPS60141052A - Trouble position searching system in digital transmission line - Google Patents

Abstract

PURPOSE:To attain trouble position searching suitable for optical fiber communication in keeping a modulation speed equal to NRZ (Non Return to zero) by using a parity code and an alteration point code as two kinds of error detection code, and applying differentiation to shape the latter in receiving side to form it into an AMI (alternate mark inversion) code. CONSTITUTION:Coding is applied to NRZ pulse train in the transmitting side, and a signal ''1'' is converted to an alteration point and a signal ''0'' is converted to a non-alteration point (or reversely). When this is differentiated to shape the form in receiving side, AMI code is obtained and searching of trouble position can be made by this. When an original signal is supplied to an input terminal 41 of an encoder, coded output is obtained in an output terminal 44 as shown in the figure (b). When this is supplied to an input terminal 50 of received waveform decoder, and waveform [shown in figure (c)] obtained by delaying it by a delay circuit 51 is subtracted from original waveform (b) by a subtracter 52, a waveform (d) is obtained. This waveform shows MI pulse train, and ''1'' and ''-1'' correspond to ''1'' of original signal, and ''0'' corresponds to ''0'' of original signal.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a fault location search method for a digital transmission line.
In particular, it relates to a search method that can detect the location of a fault in a repeater on an optical 7-eye digital transmission path with a single operation.

[Background of the invention]

The present inventors previously proposed a fault location search method in digital transmission (Japanese Patent Application No. 58-40455).

In this digital transmission path fault location search method, the transmitting terminal applies two types of error detection encoding to the original signal before transmitting it.
At each relay point, after detecting code errors using one error detection code, re-encoding is performed only on the error detection code and sending it to the next relay point, and the detected code error rate is measured. This system notifies the transmitting or receiving terminal station that a failure has occurred in the corresponding relay section, and the receiving terminal station uses the other error detection code to detect a code error in the overall line while the receiving terminal is busy with the received signal. .

FIGS. 1 and 2 are a time chart and a block diagram of digital transmission code processing showing an example of the above method.

As shown in FIG. 2, the block configuration of this method is that a fault signal sending circuit 6 is provided at each relay point, and the intervening cable 7 for transmitting the fault signal is passed through to the fault signal receiving circuit 10 of the receiving terminal station 5. Send error information. The processing function of the repeater 4 is as shown in FIG.
e Mark Inversion) The trap is set so that it is re-encoded and sent to the next section.

fa) in FIG. 1 is the original code, and since the transmitting terminal station 1 can detect errors in the error, as shown in (b), -
4-Reity encoding. As shown by the arrows, one block is made up of 6 bits, and free pulses are inserted into the shaded areas in such a way that the number of pulses in the block is an odd number (odd number ≠ right).

In (a), 2 blocks are shown, and the first pro-lock is 3 pulses, so Friti Pulse is not inserted, and the second pro-lock is 2 pulses, so the 1/4-IJ pulse is inserted. (diagonal line) has been inserted.

Next, as shown in fc), after AMI encoding, the signal is sent from the transmitter 2 to the transmission line 3.

In a normal transmission line 3, low frequency signals are blocked by a transformer and a capacitor, so in code 1 (b) VC, DC fluctuations occur in the equalized waveform sequence along with fluctuations in the mark rate of the code, making identification Playback becomes difficult.

Therefore, an AMI code (bipolar code) is used in which the polarity is reversed for each pulse and the spectrum has maximum energy near IA, which is the pulse repetition frequency.

If there is no one code error during transmission on the transmission line 3, this waveform is transmitted as is, but if an error occurs due to noise on the transmission line 3, for example as shown by the dotted line in (d),
The repeater 4 detects and registers this error, and re-encodes and transmits the next section so as to satisfy the AMI rule. In other words, the error for each section is a disturbance of the AMI rule K
If one pulse disappears as shown in Figure 1(d) after detecting the number of errors per second (error rate), the error rate as shown in Figure 1 (epic , the polarities of all the pulses in the subsequent block are inverted, and the entire pulse is re-encoded so that the polarity is reversed between positive and negative.

As a result, in the next section, the code error rate of only that section can be detected.

On the other hand, the code error rate for the entire line can be detected at the receiving terminal station 5 by returning the original code to the original code as shown in FIG. 1(f). All you have to do is monitor.

At each relay point, it is possible to detect code errors in the relay section corresponding to that relay point, so if this is registered and the error signal is sent from the fault signal sending circuit 6 when it exceeds a predetermined limit, the intervening cable 7 Fault signal receiving circuit 9 or 1 throughout
By receiving K at 0, it is possible to know in which relay section a failure has occurred. By making the frequency of the fault signal different for each relay section, it is possible to easily identify which relay section the fault signal is in by receiving the fault signal and passing it through the corresponding band-pass filter. It is also possible to add an address to each fault signal.

In the above explanation, an example was given in which an AMI code and a friti code are used together, but if the two types of codes are orthogonal, that is, if the two types of codes are not influenced by each other, any code can be combined. It is clear that it is also good. For example, on the transmitting side, the binary AMI code (11--111 or @
00', a code that converts 10" to !10" or @01"), and this is formed into duobinary by a roll-off filter on the receiving side to create an AMI code (for example, r 0ptical pulse form).
ats for fiber optic digita
l correspondence J I EEE
Trans on Commun, C0M-24r 4
4 PP 404-413. April 1976) and
By using the ~4-ity code in combination, this fault location search method can be applied even to systems such as optical communications that use binary codes on the transmitting side. The binary AMI code that converts @1" above to "11" or @00"J"0'i'lO" or @01"k is DMI (Differentia
In the following explanation, the name DMI code will be used.

When it is desirable for the waveform modulating the semiconductor laser to be binary, as in optical communication, as mentioned above, D
Since it is difficult to perform MI encoding and perform narrow band shaping on the receiving side, a method of converting it into AMI code is used. In this case, the DMI code is also used for re-encoding at the relay point.

However, DMI code fi N RZ (Non R
Since it requires double the modulation speed as compared to the (eturn to zero) code, it is unsuitable for systems using optical elements such as light emitting diodes that have a limited modulation speed.

[Purpose of the invention]

Considering the above circumstances, the object of the present invention is to
The objective is to provide a standard encoding method.

[Summary of the invention]

In order to achieve the above object, the present invention uses NRZ on the transmitting side.
Applying precoding to the pulse train, signal 11'' is at the change point,
The signal '0'' is converted to a no-change point (or vice versa). When this is differentially shaped on the receiving side, A M I (Al
ternate Mark Inversion)
A code is obtained, and the fault location can be searched from this code.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 3 to 5. FIG. 3(a) is the ld original signal, and when this is applied to the input terminal 41 of the precoder shown in FIG. 4, the output terminal 44 is shown in FIG.
An encoded output as shown in b) is obtained. This is obtained by adding the output signal and the input signal according to the modulo 2 law in an adder 42 using the modulo 2 law, and then delaying the signal by 1 bit using the delay line 43. As shown by the arrow, 11” of the original signal (a) has a waveform (bl
It can be seen that 1'0'' corresponds to the point of no change at the point of change.

The received waveform (same as Fig. 3(b)) is applied to the input terminal 50 of the decoder shown in Fig. 5, and it is delayed by the delay circuit 51 (waveform of Fig. 3 fc)). Original waveform (
By subtracting from bl by the subtractor 52, waveform (d) is obtained. This waveform is an AMI pulse train, and slm and "-1" correspond to @1" of the original signal, and @θ" corresponds to "O"K of the original signal.

Since the KAMI waveform on the receiving side is obtained as described above, the fault location can be searched using the above-described method. In other words, each repeater detects a violation of the AMI code (with an AMI code, it is normal for 1 and -1 to occur alternately; anything else is a violation), and thereby the failure status of each relay section can be detected. can be detected. After the AM code is once converted to NRZ in each intermediate device, it is pre-encoded again and sent to the next relay section.

On the other hand, by using parity in combination with the pulse train, transmission errors in the entire relay section can be monitored.

〔Effect of the invention〕

As explained above, according to the present invention 1[c, the modulation speed is set to NRZ
Since it is possible to perform a fault location search suitable for optical fiber communication while keeping the user busy, the effect is great when applied to transmission systems with limited modulation speeds such as light emitting diodes.

[Brief explanation of the drawing]

1 and 2 are time charts and block diagrams of the code processing of the fault location search method for digital transmission lines, which is the premise of the present invention, and FIGS. 3 to 5 show embodiments of the present invention. So, Figure 3 is a time chart of code processing,
FIG. 4 is a block diagram of the precoder, and FIG. 5 is a block diagram of the decoder. 41.50: Input terminal, 42: Adder based on law 2, 4
3.51: Delay circuit, 52: Subtraction circuit, 53: Output terminal. 11''A 31-A 4th X Figure 5

Claims (1)

[Claims] At the transmitting terminal station of the digital transmission path, the original signal is subjected to two types of error detection encoding and transmitted, and at each relay point, after detecting code errors using one of the two types of error detection encoding, , re-encodes only the above error detection code and sends it to the next relay section, and measures the detected code error rate to notify the transmitting or receiving end that a failure has occurred in the corresponding relay section. In the fault location search method for digital transmission lines, the receiving end station checks the received signal using the other error detection code and detects code errors in the entire line. , a parity code and an alternating son code are used, and the latter is differentially shaped on the receiving side to create AM1 (Alternate Ma
rk Inversion) A method for locating faults in digital communication routes, which is characterized by an X in the code.