JPH05167588A - Abnormality detection system of channel in local area network - Google Patents

Abstract

PURPOSE:To make it possible to accurately detect a channel abnormality generating intermittently in a LAN. CONSTITUTION:When the number of times of intermittent abnormalities of a communication channel via a T abnormal group detection logic part 12 is counted by a T abnormal group counter 13 and more than a fixed number of times of abnormalities are counted within a fixed times, this channel is decided as abnormal. Thus, since the occurrences of intermittent abnormalities can be surely detected and the abnormality state can be held till the detected abnormality is corrected, there is no possibility of the frequent repeating of the detections of abnormalities and the returns by a temporary recovery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel abnormality detecting method in a LAN capable of detecting an abnormality in a communication channel occurring on a local area network (hereinafter, LAN).

[0002]

2. Description of the Related Art In a LAN used for a control system or the like, in order to improve the reliability of the entire system, it is constantly diagnosed whether or not a communication channel is normal. Either the LAN is disconnected or the channel is switched to the other channel when the channel is duplicated so that the entire system is not affected by one abnormality. In a system with dual channels, if a channel abnormality is detected,
Periodically diagnoses the channel in which an abnormality has occurred while continuing communication using the normal channel, and if it is determined that the abnormality has been recovered, the abnormal state of that channel (recognizing that the channel is abnormal) ) Is automatically resolved. Abnormalities that occur in the LAN include permanent ones (hereinafter, P abnormality group) due to an abnormality in the hardware or software of the connected node or the transmission line itself, deterioration of elements, poor contact, or disturbance to the transmission line. There is something that occurs intermittently (hereinafter, T abnormality group), and in the case of the P abnormality group like the former, once it is judged as abnormal, the abnormal state continues unless the maintenance person repairs the abnormality thereafter. However, the T abnormality group like the latter is an uncertain one in which an abnormality occurs or does not occur each time data communication is performed.

[0003]

In the conventional system,
Since the abnormality is automatically recovered even for the T abnormality group in which the abnormality is uncertain, there is a possibility that the abnormality detection and the recovery by the temporary recovery may be repeated frequently. Had the problem that some nodes lost communication.

[0004]

In order to solve such a problem, the present invention proposes that at least one node among a plurality of nodes connected to a LAN detects a permanent abnormality and an intermittent abnormality of a communication channel. When one of the communication channels detects an intermittent abnormality a certain number of times or more within a certain period of time, the channel is determined to be abnormal. Further, at this time, the time and the number of times for detecting the abnormality of the communication channel can be arbitrarily set. In addition, some or all of abnormalities in the frame check sequence (error detection code) of the data to be communicated, inconsistencies in the frame length, and inability to detect the start code and end code of the frame are targeted for the above intermittent abnormality. ..

[0005]

When the intermittent communication channel abnormality is detected a certain number of times or more within a certain period of time, the channel is determined to be abnormal, so that the occurrence of the abnormality can be reliably detected and the detected abnormality. If the abnormal state is maintained until the is repaired, there is no fear of frequently repeating the detection of the abnormality and the recovery by the temporary recovery.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention and shows a part of functional blocks of nodes constituting a LAN. In the figure, A is a transmission line, and the transmission line A has a receiver 10 and a P abnormality group detection logic unit 1.
1, T abnormality group detection logic unit 12, T abnormality group counter 1
3, a plurality of nodes including the T abnormality group timer 14, the latches 15 and 16, and the OR circuit 17 are connected.

That is, the receiver 10 receives the data coming from the transmission path A and converts the received data to detect a permanent abnormality P abnormality group detection logic unit 11 and intermittent abnormality detection T. Abnormal group detection logic unit 12
Send to. The T-abnormality group counter 13 counts the number of T-abnormality groups detected by the T-abnormality group detection logic unit 12 within a time period based on the T-abnormality group timer 14 and sends them to the latch 16 to hold this value. The abnormality group detection logic unit 11 detects the P abnormality group based on the received data and causes the latch 15 to hold this value. The OR circuit 17 takes the logical sum of the data indicating the P abnormality group and the T abnormality group held in the latches 15 and 16 and outputs the logical sum as a channel abnormality detection signal a. In addition, b is a clock signal given to the T abnormality group timer 14, and c is a reset signal for resetting the T abnormality group counter 13.

The abnormalities included in this T abnormality group are (1) FCS (frame check sequence; Frame)
e Check Sequence) Abnormality (2) Frame length mismatch (3) Frame start / end cannot be detected, etc. In many cases, one or more bits that make up the frame are element deterioration, transmission line contact failure Alternatively, it is generated because it is changed by noise or the like induced in the transmission path. Of these, if an abnormality occurs due to noise, the effect is transient and does not affect subsequent data communication, but if an abnormality occurs due to element deterioration, etc., some kind of recovery means Unless it is taken, it is likely to occur intermittently.

An actual example of such an abnormality is shown in FIG. In this example, three nodes 1 to 3 are connected by a communication line compliant with the RS-485 standard. In this communication line, one transmission line A is composed of three signal lines [(+), (-) and common (c)], and in principle, transmission is impossible no matter which signal line is defective. Becomes However, in reality, it can often be transmitted normally depending on the electrical load and the distance between the nodes. For example, if some abnormality occurs in the signal line (-) of the node 3 as shown in FIG. 2, the communication between the nodes 2 and 3 can be normally performed, but sometimes the communication between the nodes 1 and 3 is abnormal. The situation occurs.

If the node 1 detects such a channel abnormality in such a situation (assuming that the P abnormality group does not occur at this time), no abnormality is detected in the communication with the node 2. , An abnormality is detected during communication with the node 3. The abnormality detected in the communication with the node 3 is accumulated in the T abnormality group counter 13. Since the T abnormality group counter 13 is periodically reset by the output of the T abnormality group timer 14, if the T abnormality group is detected a preset number of times or more within this period, the result is latched.
Is stored and held in the memory, and is passed through the OR circuit 17 to a processing circuit (not shown) as a channel abnormality signal a.

On the other hand, the T-abnormality group is also generated by a disturbance such as noise, but at this time, since the abnormality is temporary, the T-abnormality group counter of the T-abnormality group timer does not reach the specified count value. It is reset by the output and the channel abnormality signal a is not output. Usually, the occurrence frequency is different between the abnormality caused by noise and the T abnormality group caused by other factors. Therefore, by properly adjusting the count value of the T abnormality group counter 13 and its integration time, only the latter is accurately detected. can do. That is, if the count value and the integration time can be variably set and a value corresponding to the operating environment of the LAN is set, the T abnormality group due to factors other than noise can be accurately detected.

Next, FIG. 3 is a block diagram showing another embodiment of the present invention. This example illustrates the invention as an L for process control.
It is applied to a communication interface used for AN. In FIG. 3, 10 is a receiver, 20 is a driver, 21 is a commercially available communication LSI that performs serial / parallel conversion of transmission / reception signals, addition and inspection of error correction codes, verification of received addresses, and the like, and 22 is a microprocessor (hereinafter, uP), 23 are ROMs for storing programs executed by uP 22, and 24 is a RAM for storing data.

In FIG. 1, the counting of the T abnormality group is realized by a combination of hardware counters, but in the present embodiment, it is realized by executing the uP program. Therefore, the means for implementing the present invention may be hardware or software. That is, the T anomaly group detection program executed by the uP 22 incorporates the logic as shown in FIG. 4, and the T anomaly group integration program incorporates the logic as shown in FIG.

The T anomaly group detection program is activated when this node receives data, or when nothing is received for a certain period of time, etc., and an abnormality belonging to the T anomaly group (for example, an FCS error is detected). Etc.), and if an abnormality is detected, increment the counter T_Fail_Counter that increments the number of occurrences of the T abnormality group by +1.
However, if no abnormality is detected, nothing is done.

The T-abnormality group integration program is periodically activated by an interrupt of a timer or the like, and in this interrupt processing, T_Sample_Counter, which is a timer for determining the integration time of the T-abnormality group, is incremented by one. Then, the value of this timer is the specified integration time Sample_T.
If the iming is not reached, do nothing. If this accumulated time is reached (that is, if the T abnormality group is accumulated for a specified time), the counter T_Fail_Count is counted.
It is checked whether the value of r exceeds the set value T_Fail_Limit. If it exceeds, this notifies the other logic units that a channel abnormality has occurred due to the T abnormality group, assuming that the T abnormality group has generated a certain number of abnormality within a certain time, and resets the counter T_Fail_Counter. Also, the counter T_Fail_Count
If the value of r does not exceed the set value T_Fail_Limit, it is determined that the T abnormality group has not occurred at all or it is a temporary abnormality occurrence due to noise or the like, and the other logic units are not notified.

As described above, by using the abnormality detection method of the present invention, it is possible to reliably detect even an intermittent abnormality such that an abnormality occurs when communicating only with a specific node. In this case, there is no effect on the permanent abnormality detection.

[0017]

As described above, according to the present invention,
When the intermittent abnormality of the communication channel is detected a certain number of times or more within a certain period of time, the channel is judged to be abnormal.
Since the occurrence of an abnormality can be reliably detected and the abnormal state can be held until the detected abnormality is repaired, there is no risk of frequently repeating the abnormality detection and the recovery by the temporary recovery.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a system to which a channel abnormality detection method in a LAN according to the present invention is applied.

FIG. 2 is a diagram showing an example when an intermittent abnormality occurs in the system.

FIG. 3 is a block diagram when the present invention is implemented using a microprocessor.

FIG. 4 is an explanatory diagram showing the contents of a T-abnormality group detection program executed by the microprocessor.

FIG. 5 is an explanatory diagram showing the contents of a T abnormality group integration program executed by the microprocessor.

[Explanation of Codes] 1-3 Node 10 Receiver 11 P Abnormal Group Detection Logic Section 12 T Abnormal Group Detection Logic Section 13 T Abnormal Group Counter 14 T Abnormal Group Timer 15, 16 Latch 17 OR Circuit 20 Driver 21 Communication LSI 22 Micro Processor (uP) 23 ROM 24 RAM A Transmission path a Channel abnormality detection signal b Clock signal c Reset signal

Claims (3)

[Claims] 1. In a local area network for performing data communication between a plurality of nodes via a duplicated communication channel, at least one node of the plurality of nodes is provided with a permanent abnormality or an intermittent abnormality of each communication channel. A channel abnormality detection method in a local area network, which enables detection and determines that channel is abnormal when an intermittent abnormality is detected in one communication channel a certain number of times within a certain time. .. 2. The local area network abnormality detection method according to claim 1, wherein the time and the number of times for detecting the abnormality of the communication channel can be arbitrarily set. Channel abnormality detection method. 3. The channel abnormality detection method in a local area network according to claim 1, wherein the intermittent abnormality is a frame check sequence abnormality indicating an error detection code of data to be communicated, a frame length mismatch and a frame head code. A method of detecting an abnormality of a channel in a local area network, which is intended for a part or all of undetectable end codes and end codes.