JP2796094B2 - Transmission line failure detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] For example, regarding a transmission path failure detection method for detecting a failure in an optical cable in an exchange, a failure is detected before receiving undefined data at a receiving side, and In a transmission line fault detection system for transmitting a signal in which timing information is superimposed on data to a transmission line for the purpose of disabling reception on the reception side, when a failure occurs in the transmission line, the signal A fault clock signal having a frequency higher than the normal clock signal is output from the timing information of the fault, and the fault signal is input while the fault occurs in response to the fault clock signal, and the fault signal is output. When the clock signal transitions, a code error signal indicating that the indeterminate signal is an error in the coding rule is output at random repetition depending on the indeterminate signal, and the fault is output. In response to the code error signal which serves to prevent the reception of the receiving side of the undefined data by converting the undefined signal transition on the clock signal and configured to output a fault detection signal.

[Industrial applications]

The present invention relates to a transmission path failure detection method, for example, a transmission path failure detection method for detecting a failure of an optical cable in an exchange.

[Conventional technology]

In recent digital exchanges, in order to cope with an increase in the amount of communication information and an increase in the speed of communication, each device in the exchange is connected with an optical cable.

FIG. 5 shows the configuration of the exchange. A plurality of concentrators 512 for concentrating a plurality of subscriber lines and a switching unit 531 are connected by an optical cable. Further, a plurality of digital trunks 551 for transmitting and receiving data between the exchange 511 and another exchange (opposite station) and the switching unit 531 are connected by an optical cable.

When exchanging signals via such an optical cable, a CMI (Coded Mark Inversio) in which a timing signal such as a clock signal is superimposed on data is used as a communication signal.
n) Signs are commonly used.

For example, when the digital trunk 551 receives a CMI code sent from the switching unit 531 via an optical cable, the digital trunk 551 extracts a clock signal from the received CMI code, and further extracts data synchronized with the clock signal from the CMI code. Is extracted.

[Problems to be solved by the invention]

By the way, according to the conventional method described above, when a failure such as disconnection occurs in the optical cable, the input signal (CMI code)
In order to detect the failure of the optical cable by monitoring the state of the optical cable, there is a problem that it takes time to detect the failure.

In general, a receiving end of an optical cable converts received optical information into an electric signal and extracts a clock signal through an analog circuit such as a filter. When the signal strength at the time of extracting the clock signal becomes smaller than a predetermined value,
It detects that the input light has stopped. If an attempt is made to shorten the time until detection in such a fault detection system, there is a risk that the fault detection system will malfunction due to disturbance during normal operation, so that failure detection is performed so that malfunction due to such disturbance does not occur. The system needs to be configured. When the fault detection system is configured in such a manner, it takes about 500 μs to 1 ms from the occurrence of the fault to the output of the alarm signal from the fault detection system.

Until the alarm signal is output after the occurrence of the failure in the optical cable, indefinite data is transmitted from the CMI code decoding unit at the receiving end, so that there may be a problem in the circuit that has received the undefined data.

For example, when audio information (analog signal) is sampled into digital data at a frequency of 8 KHz, this digital data is updated every 125 μs, and the receiving side of the data receives indefinite data every 125 μs. .

In particular, when a failure occurs in the optical cable connecting the switching unit 531 and the digital trunk 551, undefined data is transmitted to a plurality of lines connecting the exchanges via the digital trunk 551 (time-division multiplexing is performed between the digital trunks). And transmission of undefined data is transmitted as a time slot to indicate which channel in one frame is being used), and all of these lines may be confused. Therefore, there has been a demand for a method of shortening the time for detecting a failure and preventing transmission of indefinite data.

The present invention has been made in view of such a point, and a transmission path failure detection method capable of detecting a failure before receiving uncertain data on a receiving side and disabling reception on the receiving side of the uncertain data. It is intended to provide.

[Means for solving the problem]

FIG. 1 is a block diagram showing the principle of the first and second aspects of the present invention.

In the figure, the timing information extracting means 111 in the transmission path failure detection method when transmitting a signal in which timing information is superimposed on data to the transmission path 191 extracts timing information from the signal via the transmission path 191 and When the signal is monitored and a failure in the transmission line 191 is detected, timing information with a shorter time interval than the timing information before the failure is detected is output.

The data extraction means 121 is a means for extracting the timing information
Based on the timing information output in 11, data is extracted from the signal, and an error signal is output when an error in the extracted data is detected.

The fault detecting means 131 outputs a fault detecting signal in response to the error signal output from the data extracting means 121.

According to the first aspect of the present invention, the timing information extracting means 111
And the data extracting means 121 and the fault detecting means 131.

According to a second aspect of the present invention, in the transmission path failure detection system according to the first aspect, the timing information extracting means 111 outputs an alarm signal when detecting a failure in the transmission path 191.
The output of the alarm signal is stopped when the fault of the transmission line 191 is restored, and the fault detecting means 131 is configured to stop the output of the fault detection signal in response to the stopped alarm signal.

(Operation)

According to the first aspect of the present invention, a signal in which data and timing information are superimposed is introduced into the timing information extracting means 111 and the data extracting means 121 via the transmission line 191.

The timing information extracting means 111 extracts timing information from the introduced signal, and the data extracting means 121 extracts data based on the timing information.

Further, the timing information extracting unit 111 monitors the introduced signal, and outputs a timing information having a shorter time interval than the timing information before the failure occurs when a failure occurs in the transmission line 191.

Then, based on the timing information output from the timing information extracting means 111, the data extracting means 121 outputs an error signal when detecting an error in the extracted data.

The failure detection unit 131 outputs a failure detection signal in response to the error signal output from the data extraction unit 121.

Therefore, when a failure occurs in the transmission path 191, it is possible to detect the failure before receiving the undefined data on the receiving side and eliminate reception of the undefined data on the receiving side.

According to a second aspect of the present invention, the timing information extracting means 111 constituting the first aspect of the present invention outputs an alarm signal when detecting a failure in the transmission line 191, and outputs the alarm signal when the failure in the transmission line 191 is recovered. Stop output of alarm signal. The failure detecting means 131 stops outputting the failure detection signal in response to the stopped alarm signal.

Therefore, the device that receives the failure detection signal can recognize when a failure has occurred and when the failure has been recovered.

〔Example〕

Hereinafter, embodiments of the invention described in claims 1 and 2 will be described in detail with reference to the drawings.

FIG. 2 shows a configuration of an embodiment to which the transmission path fault detection system according to the first and second aspects of the invention is applied.

I. Correspondence relationship between the embodiment and FIG. 1 Here, the correspondence relationship between the embodiment of the invention described in claim 1 and claim 2 and FIG. 1 will be described.

The timing information extracting means 111 includes the optical-electrical conversion circuit 21.
0, which corresponds to the clock extraction circuit 211.

The data extracting means 121 corresponds to the optical-electrical conversion circuit 210 and the decoding circuit 221.

 The failure detecting means 131 corresponds to the protection circuit 231.

 The transmission path 191 corresponds to the optical cable 291.

The alarm signal corresponds to the alarm signal output from the clock extraction circuit 211.

The error signal corresponds to a code error signal output from the decoding circuit 221.

The failure detection signal corresponds to a cable disconnection signal output from the protection circuit 231.

Assuming that the above-mentioned correspondence exists, an embodiment of the present invention will be described below.

II. Configuration of Embodiment In FIG. 2, the fault detection circuit of the embodiment to which the transmission line fault detection method according to the first and second aspects of the invention is applied is provided at the receiving end of each optical cable.

This fault detection circuit is an optical-electrical conversion circuit 210 that converts optical information received via the optical cable 291 into an electric signal.
And a signal (electric signal) converted by the optical-electrical conversion circuit 210
Clock extraction circuit 211 that extracts a clock signal from
A decoding circuit 221 for extracting data from the signal converted by the optical-electrical conversion circuit 210; and a protection circuit 23 for outputting a cable disconnection signal in response to a failure (for example, disconnection) of the optical cable 291.
With one.

The optical information via the optical cable 291 is transmitted to an optical-electrical conversion circuit 210.
Supplied to The output end of the optical-electrical conversion circuit 210 is connected to the clock extraction circuit 211 and the decoding circuit 221. The output terminal of the clock extraction circuit 211 is connected to the decoding circuit 221 and the protection circuit 231. The output terminal of the decoding circuit 221 is connected to the protection circuit 231.

Further, the protection circuit 231 includes an R-S
Type flip-flop (RS-FF) 239, a delay circuit 233 for delaying the data phase, an inverter 235, and an AND gate 2
37.

In the protection circuit 231, a signal (alarm signal) introduced from the clock extraction circuit 211 is supplied to one input terminal of the AND gate 237 via the delay circuit 233,
The signal is supplied to the other input terminal of the AND gate 237 via the inverter 235. The output terminal of the AND gate 237 is connected to the reset input terminal R of the RS-FF239. The signal (code error signal) introduced from the decoding circuit 221 is RS
It is supplied to the set input terminal S of -FF239. The signal (cable break signal) output from the output terminal Q of RS-FF239 is
Output to the outside from the fault detection circuit.

III. Operation of Embodiment Next, the operation of the transmission line fault detection system according to the embodiment of the present invention will be described.

In the embodiment, a CMI code is used as an encoding method for superimposing a clock signal on data, and its outline is shown in FIG.

As shown in the figure, for example, when data “01011001” is encoded, the bit “0” of a bug in the data string is converted into a signal that changes from a low state to a high state in the middle of a 1-bit data cycle, and the bit “1” is converted. "Is converted to a low or high state signal that does not change within the cycle. The low state and the high state corresponding to the bit “1” are arranged so as to appear alternately.

Therefore, the decoding circuit 221 monitors a signal input from the optical-electrical conversion circuit 210, and outputs a code error signal when a signal that violates this coding rule is supplied. As described above, in the CMI code, a signal that changes from a high state to a low state in the middle of a cycle is recognized as an error, and the polarity of the mark (the state of the signal corresponding to bit “1”)
An error can be recognized according to When these errors are recognized, the decoding circuit 221 outputs a code error signal.

FIG. 4 shows the operation timing of the embodiment. In the figure, “clock signal” indicates the clock signal extracted by the clock extraction circuit 211, and “data” indicates the decoding circuit 22.
The signal extracted in 1 is converted into a signal A by a delay circuit 2
33 indicates a signal supplied to the AND gate 237, “Signal B” indicates a signal supplied to the AND gate 237 via the inverter 235, and “Signal C” indicates a signal output from the AND gate 237. .

 Hereinafter, FIG. 2 to FIG. 4 will be referred to.

When optical information is introduced into the optical-electrical conversion circuit 210 via the optical cable 291, the optical-electrical conversion circuit 210 converts the optical information into an electric signal and outputs it. The signal output from the photoelectric conversion circuit 210 is supplied to the clock extraction circuit 211 and the decoding circuit 221.

The clock extraction circuit 211 extracts a clock signal according to the introduced signal. The decoding circuit 221 extracts data synchronized with the clock signal from the signal introduced from the optical-electrical conversion circuit 210.

During the above communication operation (during data extraction operation), the optical cable
When a failure (for example, cable disconnection) occurs in 291, first, the clock signal output from the clock extraction circuit 211 is based on the oscillation state. The decoding circuit 22
In step 1, indefinite data is output in accordance with a signal input from the optical-electrical conversion circuit 210 (an undefined signal due to disconnection of the optical cable 291).

Note that the clock extraction circuit 2
From 11, a clock signal (fault-time clock signal) having a frequency approximately four to five times the frequency of the clock signal that is normally extracted is output. By oscillating the clock signal in this way, the state maintenance and subsequent recovery processing in the clock extraction circuit 211 are facilitated.

Then, the decoding circuit 221 checks whether or not the indefinite signal input from the optical-electrical conversion circuit 210 has a coding rule error. Since the data decoded by the decoding circuit 221 becomes indefinite data, an error in the coding rule is detected by random repetition depending on the indefinite data, and an error in the coding rule is detected from the decoding circuit 221. The indicated code error signal is output at random repetition depending on the input indefinite signal.

After the failure is detected, an alarm signal is output from the clock extraction circuit 211 after a predetermined time (500 μs to 1 ms) set so that the alarm signal generation circuit portion of the clock extraction circuit 211 does not malfunction due to disturbance during normal operation.

The code error signal output from the decoding circuit 221 is
It is supplied to the set input terminal S of the RS-FF 239 in the protection circuit 231. The RS-FF 239 is set according to the code error signal supplied first, and thereafter the cable disconnection signal “1” is output from the RS-FF 239.

Since this cable disconnection signal is output almost at the same time as the cable disconnection (a delay due to the coding rule check occurs)
The receiving side of the data output from the encoding circuit 221 can recognize the subsequent data as indefinite data and invalidate it.

Next, when the failure of the optical cable 291 is restored, the output of the code error signal output intermittently from the decoding circuit 221 stops, and the output of the alarm signal output from the clock extraction circuit 211 stops. . Protection circuit 231
From the AND gate 237, the logic “1” of the delay time width by the delay circuit 233 after the stop of the alarm signal is output.
The output "1" of the AND gate 237 is supplied to the reset input terminal R of the RS-FF239, and the RS-FF239 is reset. In response to this reset operation, the output of the cable disconnection signal output from the RS-FF 239 (protection circuit 231) stops.

IV. Summary of Embodiment As described above, when a failure occurs in the optical cable 291 and a signal containing a coding rule error is supplied, the decoding circuit 221
Outputs an intermittent code error signal, and then outputs an alarm signal from the clock extraction circuit 211.
The RS-FF 239 in the protection circuit 231 is set according to the first code error signal output from the decoding circuit 221, and the protection circuit 231 outputs a cable disconnection signal. Thereafter, the device that has received the cable disconnection signal can recognize the indefinite data.

When the failure of the optical cable 291 is recovered and the alarm signal output from the clock extraction circuit 211 stops, the RS-FF239 in the protection circuit 231 responds to the stop of the alarm signal.
Is reset, and the cable disconnection signal output from the protection circuit 231 stops.

Therefore, by detecting the cable disconnection of the optical cable 291 by the cable disconnection signal corresponding to the error in the coding rule, the time required for the failure detection can be reduced, and it is possible to recognize the indefinite data output thereafter. Become.

For example, in the digital trunk 551 of the exchange 511 shown in FIG. 5, by detecting the disconnection of the optical cable quickly, the digital trunk 551 does not need to send undefined data to the opposite station, and all the multiplexed lines are disrupted. You will not be forced to do it.

V. Modifications of the Invention In the above-described embodiments of the first and second aspects of the present invention, the case where CMI-encoded data is received via the optical cable 291 has been considered. The present invention can be applied to any multiplexed transmission path (such as a coaxial cable) other than the optical cable 291 as long as it is an encoding method (CMI encoding or the like) that can detect the signal.

Further, in the embodiment, even if the code error signal is output even once, the cable disconnection signal is output in accordance with the output, so that it is effective for a transmission system having a low error occurrence frequency of about 10 ⁻⁷ to 10 ^−9. But the frequency of errors is high (10 ^-3 to 10 ^-6
The present invention is applied to a transmission system by outputting a code error signal when two or more errors occur in four bits, for example. Can be.

Further, in "I. Correspondence between the embodiment and FIG. 1",
The correspondence between the inventions described in claims 1 and 2 and the embodiments has been described. However, the present invention is not limited to this, and it is understood by those skilled in the art that the present invention has various modifications. You can easily guess.

〔The invention's effect〕

As described above, according to the first aspect of the present invention, it is determined whether or not an indeterminate signal has a coding rule error at a transition time of a failure time clock signal generated when a failure occurs in a transmission path. Of the code error signals generated in the above, the code error signal which can invalidate the reception of the undefined data converted from the undefined signal on the receiving side is used for generating the failure detection signal. Side can prevent reception.

Further, according to the second aspect of the present invention, it is possible to cancel the failure detection signal generated by the first aspect of the present invention by an alarm signal generated in a conventional manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the principle of a transmission path failure detection system according to the first and second aspects of the invention; FIG. 2 is a transmission path failure detection method according to the first and second aspects of the invention; FIG. 3 is an explanatory diagram of a CMI code, FIG. 4 is an operation timing diagram of the embodiment, and FIG. 5 is a configuration diagram of an exchange. In the figure, 111 is timing information extraction means, 121 is data extraction means, 131 is fault detection means, 191 is a transmission line, 210 is an optical-electrical conversion circuit, 211 is a clock extraction circuit, 221 is a decoding circuit, and 231 is protection. Circuit, 233 is a delay circuit, 235 is an inverter, 237 is an AND gate, 239 is an RS-FF, 291 is an optical cable, 511 is an exchange, 521 is a concentrator, 531 is a switching unit, 541 is a control unit, and 551 is a digital trunk. is there.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takashi Nara 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-62-108623 (JP, A) JP-A-58-209251 (JP, A) JP-A-61-49542 (JP, A) JP-A-62-92554 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04L 25/02 H04L 25 / 49 H04M 3 / 22,3 / 24

Claims (2)

(57) [Claims] In a transmission line fault detection system for transmitting a signal in which timing information is superimposed on data to a transmission line, timing information is extracted from a signal transmitted through the transmission line, and the signal is monitored. Timing information extracting means for outputting timing information at a time interval shorter than the timing information before the failure is detected when the transmission path failure is detected, based on the timing information output by the timing information extracting means, Data extraction means for extracting data from the data and outputting an error signal when an error in the extracted data is detected, and fault detection for outputting a fault detection signal in response to the error signal output from the data extraction means And a transmission path failure detection method. 2. The transmission line fault detection system according to claim 1, wherein said timing information extracting means outputs an alarm signal when detecting a fault in said transmission line, and said alarm signal when recovery from said transmission line fault is detected. And output of the fault detection means,
A transmission path failure detection method, wherein output of a failure detection signal is stopped in response to the stopped alarm signal.