JPH01170244A - Fault supervision system for local area network - Google Patents

Abstract

PURPOSE:To find out early a fault of a normal transmission signal level of other station by sampling a received transmission signal level of each station in the timing generated by using a frame reception detection means of a transmission signal and comparing the level with the normal transmission signal level of each transmission signal level set in a supervising device. CONSTITUTION:A microprocessor 15 samples the transmission signal level from each station connected to an optical star coupler 1 in the timing of receiving a D frame to detect the transmission signal level of each station connected to an optical star coupler 1 and it is compared with the normal transmission signal level of each station set in a memory 16 and when it is judged that the transmission signal level is faulty, an alarm signal 20 is outputted to a supervision panel connected to a supervising device 19, a host computer and a display device or the like. Thus, a small signal level fluctuation unable to be detected by the supervision of the reception error rate only is detected and the fault is found out in an early stage when the fluctuation of the signal level is still small.

Description

[Detailed description of the invention] [Industrial use! 7] The present invention relates to a local area network fault monitoring method for detecting abnormalities in the level of transmitted signals in a bus-type optical LAN.

[Prior art] LAN (Local Area Network)
k) has rapidly become widespread in recent years. LANs that take advantage of the characteristics of optical fibers, such as excellent noise resistance and suitability for high-speed data communications, are increasingly being used.

LAN systems using optical fibers include the loop type, in which one station is connected in a loop with optical fibers.

There is a bus type that connects like a bus. Of these, bus type LA
A star coupler, which is a passive optical branching and coupling circuit, is often used for N. In bus type LAN, a signal transmitted by one station is received by all stations connected to the LAN. Because of this, it is possible for one station to monitor the transmission status of other stations on the LAN.

Conventionally, a monitoring method for detecting abnormalities in the level of transmission signals of this type of LAN has not been considered.

Similar to this is a signal collision detection method. An example is shown in FIG.

In FIG. 3, each station is connected by an optical star coupler 1, transmitting optical fibers 2a to 2c, and receiving optical fibers 3a to 3C. The transmission signal generated from the light emitting element 34 of the transmitter 35 of the other station is sent to the local station via the receiving optical fiber 3C connected to the optical star coupler l, and is converted into an electrical signal by the light receiving element 24. , and is amplified by an amplifier 25. The output signal 26 of the amplifier 25 is sent to the waveform shaping circuit 27
and the output of the integrating circuit 28 is input to the comparator 30. If the judgment threshold 31 is set to a value larger than the output signal 32 of the integrating circuit 28 for the own station transmission signal, the transmission line If there is no collision between the local station signal and the other station signal at E, the significant signal 33 is not output from the comparator 30. However, if there is a collision between the local station signal and the other station signal at transmission path -H, , the output signal 26 of the amplifier 25 has a large amplitude. Output signal 32 of the integrating circuit 28 based on this signal
If it becomes larger than the determination 1m (fi31), the comparator 30 outputs a significant signal 33, and it is possible to detect that a signal collision has occurred.

In order to be able to detect that a collision has occurred even if the transmitted signal of the own station collides with the transmitted signal of any other station, it is necessary to The value may be set between the output and the sum of the integral value output of the own station signal and the integral value output of the minimum level signal among the signals of other stations.

[Problems to be Solved by the Invention] According to the signal collision detection method described in I-, it is possible to detect a collision between a local station transmission signal and another station transmission signal. However, it was not possible to detect abnormalities with low optical signal levels due to failures in other stations.

On the other hand, in a bus-type optical LAN such as a token bus system, it is possible to detect abnormalities in the own station and other stations by monitoring token bus failures and reception errors at each station. However, if the light level is - - fixed, the bit error rate will be extremely low 4+rI, and even a slight change in the received light level will not cause a token bus failure or reception error, and it will not be abnormal until the received light level drops significantly. will be detected. For this reason, there were problems in terms of detecting abnormalities in the 1N stage and preventing IFs from occurring.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and to provide a fault monitoring system for a local area network that can detect an abnormality in the normal transmission signal level of another station.

[Means for Solving the Problems] The local area network failure monitoring method of the present invention is based on a bus-type optical system using an optical star coupler, in which a transmitted signal from any station can be directly received by all stations. a LAN, and a monitoring device connected to a pair of input/output terminals of the optical star coupler of the LAN; By sampling at the specified timing and comparing it with the normal transmission signal level of each station set in the monitoring device, it is determined whether the transmission signal level from each station is abnormal.

[Production] In the monitoring method of the present invention, the level of the transmitted signal from each station is detected by detecting the level of the transmitted signal from each station and comparing it with the regular transmitted signal level of each station set in the monitoring device. Monitor for abnormalities. Therefore, small signal level fluctuations that cannot be detected only by monitoring the reception error rate can be detected. Abnormalities can be detected at an early stage.

[Example] Hereinafter, an uninvented example will be described based on FIGS. 1 and 2.

In FIG. 1, 1 is an optical star coupler, 2a to 2c are transmitting optical fibers, 3a to 3c are receiving optical fibers, 19
indicates the entire monitoring device.

Optical transmission signals transmitted from each station through the transmission optical fibers 2a to 2c are distributed by the optical star coupler l and sent to all of the reception optical fibers 3a to 3c. The optical transmission signal sent to the receiving optical fiber 3c is received by the light receiving element 4 of the monitoring device 19 and amplified by the amplifier 5.

6 is the transmission signal level A2 of each station from the output AI of amplifier 5
A low-pass filter amplifier 7 detects the level A2 of the transmission signal of each station obtained from this low-pass filter number amplifier 6.
8 is an A/D conversion circuit that A/D converts this sampled and held analog output and outputs it as a digital signal DI; 9 is the output of this A/D conversion circuit 8, i.e. The digital signal DI, which is the digital value of the transmission signal level of the data transmitted from other stations,
f3 This is an interface circuit that outputs to the LE/<SLO, and also has a function of creating a level monitor command C1 from the digital signal DI.

12 is a timing extraction/decoding circuit that receives the output AI of the amplifier 5 through a comparator 11, extracts and decodes the timing signal in the transmission signal of each station, and outputs the decoded signal S2; 13 receives the monitor command CI; A sampling circuit that operates as a frame reception detecting means for a transmission signal detects a specific pattern representing the start of a data frame in the decoded signal S2, and at the timing when this frame is received, sends a signal to the sample and hold circuit 7. Give sample command C2 (see (d) in Figure 2), and
This sampling circuit 13 is connected to the terminal r of the sample command C2.
14 and 15 are a communication control LSI and a microprocessor connected to the local bus IO, respectively, which output an A/D command C3 to the A/D conversion circuit 8 (see (e) in FIG. 2). LS114 is the decoded signal s
2, it detects that another station has transmitted data, and functions to issue a data reception interrupt to the microprocessor 15. Reference numeral 16 denotes a writable and readable memory connected to the local bus IO, and this memory 16 stores (/i) of the normal transmission signal level of each station.18
is an output amplifier for extracting the level A2 of the transmission signal of each station from the low-pass filter amplifier 6 in the form of an analog signal.

Next, the operation will be explained.

The microprocessor 15 samples the transmission signal level from each station connected to the optical star coupler l at the timing when the data frame is received, and detects the transmission (a signal level) of each station connected to the optical star coupler l. Then, it compares this with the normal transmission signal level of each station set in the memory 16, and if it is determined that the transmission signal level is abnormal, a monitoring board connected to the monitoring device 19.

An alarm signal 20 is output to a host computer, display device, etc.

Hereinafter, details of the operations described in -H will be explained with reference to FIG. It is assumed that the level monitor command Ct (FIG. 2(c)) has already been generated.

The optical transmission signals (FIG. 2 (a)) transmitted from each station through the transmission optical fibers 2a to 2c are distributed by the optical star coupler l and sent to the monitoring device 1 via the reception optical fiber 3C.
9, is received by the light receiving element 4, and is sent to the amplifier 5.
is amplified. The output A1 of this amplifier 5 is passed through a comparator 11 and a timing extraction/decoding circuit 12 to a communication control LSI 14, and is also passed through a low-pass filter amplifier 6 to a sample and hold circuit 7. The time constant of the low-pass filter of the low-pass filter amplifier 6 is i
f! ! is set to a reasonable value.

The sampling circuit 13 detects a specific pattern representing the start of a data frame in the decoded signal S2 and generates a sample command C2 (FIG. 2(d)) to the sample hold circuit 7. The output of the low-pass filter amplifier 6 is sampled by the sample-and-hold circuit 7, and the value at this time is held. At the end of sample command C2, sampling circuit 1
3, an A/D command C3 (FIG. 2 (E)) is output to the A/D conversion circuit 8. The output of sample hold circuit 7 is A
A/D conversion is performed by the /D conversion circuit 8, and the digital signal D
I (FIG. 2), the interface circuit 9
The signal is output to the local bus 10 via .

- On the other hand, the communication control LS 114 detects that another station has transmitted data and issues a data reception interrupt to the microprocessor 15. The microprocessor 15 accepts this and takes in the digital signal DI, which is the digital value of the transmission signal level of the other station transmission data, from the interface circuit 9 via the local bus 10. The microprocessor 15 is.

The transmitting station is known by referring to the source address of the data transmitted by another station, and the normal transmitting signal level of the transmitting station stored in the memory 16 and the digital signal DI of the transmitting signal level taken in from the interface circuit 9 are determined. Compared to,
Determine whether the transmit signal level is normal. If it is determined that there is an abnormality, the microprocessor 15
outputs an alarm signal 20 to a monitoring panel, host computer, display device, etc. through an interface circuit 17 connected to the local bus IO. At this time, if the address of the station whose transmission signal level is abnormal is also output as the contents of the alarm signal 20, the station whose transmission signal level is abnormal can be specified.

If the transmitting station address cannot be read due to a drop in the transmitting signal level, the microprocessor 15 reads the memory 1
A warning is output by comparing the signal level with the minimum normal transmission signal level of each station stored in 6.

In the embodiment described in E, the sampling circuit 13 is used as a frame reception detecting means for a transmission signal, and the sampling circuit 13 detects the start of a data frame and issues a sample command C to the sample hold circuit 7.
However, if the communication control LS114 has a function to recognize the start of a data frame, the communication control LS1
14 may be used to generate the sample command C2.

As described above, the present invention compares the transmission signal level of each station with the normal transmission signal level of each station set in the monitoring device to determine whether the transmission signal level from each station is abnormal. Monitor. Therefore, it is possible to detect small signal level fluctuations that would be difficult to detect only by monitoring the reception error rate. Since abnormalities are discovered at an early stage when signal level fluctuations are still small, system reliability can be improved, and this is extremely effective as failure prevention in critical systems.

[Brief explanation of the drawing]

FIG. 1 shows monitoring using the monitoring method of the present invention! FIG. 2 is a block diagram showing the configuration of the Ic location, FIG. 2 is a signal waveform diagram of each part in the monitoring device of FIG. 1, and FIG. 3 is a block diagram for explaining the configuration of a conventional signal collision detection system. In the figure, l is an optical star coupler, 2a to 2c are transmitting optical fibers, 3a to 3c are receiving optical fibers, 4 is a light receiving element,
5 is an amplifier, 6 is a low-pass filter amplifier, 7 is a sample hold circuit, 8 is an A/D conversion circuit, 9 is an interface circuit, 11 is a comparator, and 12 is a timing extraction circuit.
A decoding circuit, 13 a sampling circuit, 14 a communication control LSI, 15 a microprocessor, and 16 a memory. 17 is an interface circuit, 18 is an output amplifier, and 19 is a monitoring device.

Claims (1)

[Claims] A bus-type optical LAN using an optical star coupler in which a transmission signal from any station can be directly received by all stations, and the L
a monitoring device connected to the pair of input/output terminals of the optical star coupler of the AN, and in this monitoring device, the level of the received transmission signal of each station is determined at the timing generated using the frame reception detection means of the transmission signal. sample,
1. A fault monitoring method for a local area network, characterized in that it is determined whether or not a transmission signal level from each station is abnormal by comparing it with a normal transmission signal level of each station set in a monitoring device.