JP2014135591A - Network monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a network load in a network monitoring system.SOLUTION: In a network monitoring system 100, a monitoring device 10 and a device to be monitored 20 are connected via a LAN network 30. The device to be monitored 20 is provided with a state detection unit 24 for detecting the state of the device itself, a transmission unit 22 for transmitting state information on the device to be monitored 20 to the monitoring device 10, and a transmission interval adjustment unit 26 for adjusting an interval at which the state information is transmitted by the transmission unit 22. The monitoring device 10 is provided with a state determination unit 14 for determining the state of the device to be monitored 20 on the basis of the state information received from the device to be monitored 20 via the LAN network 30. The transmission interval adjustment unit 26 extends a state information transmission interval to make it longer than before when the device to be monitored 20 is normal for a prescribed period from when transmission of the state information at a given transmission interval started.

Description

  The present invention relates to a network monitoring system, and more particularly to a network monitoring system that monitors a state of a monitoring target device connected by a network using a monitoring device.

  2. Description of the Related Art Conventionally, a network monitoring system that monitors the normality of a monitoring target device by communicating between the monitoring device and the monitoring target device is known (see, for example, Patent Document 1).

JP-A-8-102755

  In the network monitoring system, information indicating the device status is periodically transmitted from the monitoring target device to the monitoring device. Therefore, when the number of devices to be monitored connected to the network increases, communication traffic increases and the load on the network increases, which may affect the communication of devices connected to the network.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a network monitoring system capable of suppressing a load on the network.

  In order to solve the above problems, a network monitoring system according to an aspect of the present invention is a network monitoring system in which a monitoring device and a monitoring target device are connected via a network. The monitoring target device adjusts the state detection unit that detects the state of the monitoring target device, the transmission unit that transmits the status information of the monitoring target device to the monitoring device, and the interval at which the transmission unit transmits the state information. A transmission interval adjustment unit. The monitoring device includes a state determination unit that determines the state of the monitoring target device based on the state information received from the monitoring target device via the network. The transmission interval adjustment unit makes the transmission interval of the state information longer than before when the monitoring target device is normal for a predetermined period after starting transmission of the state information at a certain transmission interval.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between an apparatus, a method, a system, a program, a recording medium storing the program, and the like are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the network monitoring system which can suppress the load of a network can be provided.

It is a figure for demonstrating the network monitoring system which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the structure of the network monitoring system which concerns on 1st Embodiment. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 1st Embodiment when a monitoring object apparatus and a network are normal. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 1st Embodiment when abnormality generate | occur | produces in the monitoring object apparatus. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 1st Embodiment when a failure generate | occur | produces in a network. It is a figure for demonstrating the network monitoring system which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the structure of the network monitoring system which concerns on 2nd Embodiment. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 2nd Embodiment when a monitoring object apparatus and a network are normal. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 2nd Embodiment when abnormality generate | occur | produces in the monitoring object apparatus. It is a figure for demonstrating operation | movement of the network monitoring system which concerns on 2nd Embodiment when a failure generate | occur | produces in a network.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram for explaining a network monitoring system 100 according to the first embodiment of the present invention. As shown in FIG. 1, the network monitoring system 100 is a system in which a monitoring device 10 and first to fourth monitoring target devices 20_1 to 20_4 monitored by the monitoring device 10 are connected via a LAN network 30. is there.

  In the network monitoring system 100, each monitoring target device detects whether its own operating state is normal or abnormal, and periodically transmits the detection result to the monitoring device 10 via the LAN network 30. The monitoring device 10 monitors the operation state of each monitoring target device and the state of the network between the monitoring device 10 and each monitoring target device based on information received from each monitoring target device.

  FIG. 2 is a diagram for explaining the configuration of the network monitoring system 100 according to the first embodiment. Each block shown in the present specification can be realized in hardware by an element such as a CPU of a computer or a mechanical device, and is realized in software by a computer program or the like. Depicts functional blocks realized by. Therefore, those skilled in the art will understand that these functional blocks can be realized in various forms by a combination of hardware and software.

  First, the configuration of the monitoring target device 20 will be described. As illustrated in FIG. 2, the monitoring target device 20 includes a transmission unit 22, a state detection unit 24, and a transmission interval adjustment unit 26. The state detection unit 24 periodically detects whether its own operation state is normal or abnormal. The “state information” detected by the state detection unit 24 is sent to the transmission unit 22.

  The transmission interval adjustment unit 26 adjusts the interval at which the transmission unit transmits information to the monitoring device 10. The “transmission interval information” set by the transmission interval adjustment unit 26 is sent to the transmission unit 22.

  The transmission unit 22 collectively sets “status information” and “transmission interval information” as “diagnosis information”, and periodically transmits the information to the monitoring apparatus 10 via the LAN network 30.

  As described above, the transmission interval of diagnostic information is adjusted by the transmission interval adjustment unit 26. In this embodiment, the transmission interval adjustment unit 26 starts normal transmission of diagnostic information at a certain transmission interval, and this monitoring target device 20 is normal for a predetermined period (this period is referred to as “confirmation period”). The transmission interval of diagnostic information is set longer than before. Specifically, a new transmission interval is obtained by adding a predetermined extension time to the previous transmission interval. Thereby, network traffic is reduced and the load on the network is suppressed. The transmission interval adjustment unit 26 repeats the process of increasing the transmission interval until the diagnostic information transmission interval reaches a predetermined maximum transmission interval. The reason for providing the maximum transmission interval is to prevent the transmission interval from being extended without limit. In addition, when an abnormality of the monitoring target device 20 is detected by the state detection unit 24, the transmission interval adjustment unit 26 adjusts the transmission interval of the state information to a predetermined minimum transmission interval. This is to reduce the time lag of abnormality detection in the monitoring device 10 when an abnormality occurs.

  Next, the configuration of the monitoring device 10 will be described. As illustrated in FIG. 2, the monitoring device 10 includes a reception unit 12, a state determination unit 14, and a network failure determination unit 16.

  The receiving unit 12 receives diagnostic information from the monitoring target device 20. The receiving unit 12 extracts state information from the received diagnostic information and sends it to the state determining unit 14. In addition, the receiving unit 12 extracts transmission interval information from the received diagnostic information and sends it to the network failure determination unit 16.

  The state determination unit 14 determines the state of the monitoring target device 20 based on the state information. That is, if the status information is “normal”, it is determined that the monitoring target device 20 is normal, and if the status information is “abnormal”, it is determined that the monitoring target device 20 is abnormal.

  The network failure determination unit 16 determines that a failure has occurred in the LAN network 30 between the monitoring device 10 and the monitoring target device 20 when the next diagnosis information does not arrive at a transmission interval acquired from certain transmission interval information. Specifically, the network failure determination unit 16 predicts the reception time of the next diagnosis information based on the transmission interval information, and determines that the LAN network 30 is normal if the diagnosis information is received as predicted, If diagnostic information is not received as expected, it is determined that a failure has occurred in the LAN network 30.

  Note that FIG. 2 illustrates how diagnostic information is sent from one monitoring target device 20 to the monitoring device 10, but actually, a plurality of monitoring target devices 20 are included in the LAN network 30 as illustrated in FIG. 1. Are connected, and diagnostic information is periodically transmitted from each monitoring target device 20 to the monitoring device 10.

FIG. 3 is a diagram for explaining the operation of the network monitoring system according to the first embodiment when the monitoring target device and the network are normal. In the following description, it is assumed that the transmission interval adjustment unit 26 of the monitoring target device 20 is set as follows. Of course, the following settings are examples and can be changed as appropriate.
Minimum transmission interval: 1 minute Confirmation period: 3 days Extension time: 2 minutes Maximum transmission interval: 60 minutes

  First, immediately after the monitoring target device 20 is activated, the transmission interval adjustment unit 26 of the monitoring target device 20 sets the transmission interval of the diagnostic information to the minimum transmission interval = 1 minute. Then, the transmission unit 22 continues to transmit diagnostic information to the monitoring device 10 at 1-minute intervals. The diagnosis information includes status information (ie, normal) and transmission interval information (ie, 1 minute interval). On the other hand, the monitoring device 10 waits for reception of diagnostic information at 1-minute intervals. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 is normal based on the state information. The network failure determination unit 16 predicts the next diagnosis information reception time based on the transmission interval information, and determines that the LAN network 30 is normal if the diagnosis information is received as predicted.

  When the monitoring target device 20 is normal for 3 days after starting transmission of diagnostic information at an interval of 1 minute, the transmission interval adjustment unit 26 adds an additional time of 2 minutes to the previous transmission interval of 1 minute. 3 minutes is set as a new transmission interval. Then, the transmission unit 22 continues to transmit diagnostic information to the monitoring device 10 at intervals of 3 minutes. The diagnostic information includes status information (that is, normal) and transmission interval information (that is, an interval of 3 minutes). On the other hand, the monitoring device 10 waits for reception of diagnostic information at intervals of 3 minutes. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 is normal based on the state information. The network failure determination unit 16 predicts the next diagnosis information reception time based on the transmission interval information, and determines that the LAN network 30 is normal if the diagnosis information is received as predicted.

  Similarly, when the monitoring target device 20 is normal for 3 days after starting transmission of diagnostic information at intervals of 3 minutes, the transmission interval adjustment unit 26 extends the extension time 2 to 3 minutes that is the transmission interval until then. 5 minutes including the minute is set as a new transmission interval. The transmission unit 22 continues to transmit diagnostic information to the monitoring device 10 at intervals of 5 minutes. The diagnostic information includes status information (that is, normal) and transmission interval information (that is, every 5 minutes). On the other hand, the monitoring device 10 waits for reception of diagnostic information at intervals of 5 minutes. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 is normal based on the state information. The network failure determination unit 16 predicts the next diagnosis information reception time based on the transmission interval information, and determines that the LAN network 30 is normal if the diagnosis information is received as predicted.

  The transmission interval adjustment unit 26 repeats the above processing until the transmission interval of the diagnostic information reaches the maximum transmission interval (that is, 60 minutes). Thereafter, diagnostic information is continuously transmitted at 60-minute intervals until an abnormality occurs in the monitoring target device 20.

  For example, compared with the case where diagnostic information is always transmitted at intervals of 1 minute, the communication traffic of diagnostic information in the network monitoring system 100 according to the present embodiment decreases from 3 days after the start of the apparatus, and at the maximum transmission interval of 60 minutes. When the diagnosis information is transmitted, it becomes 1/60.

  FIG. 4 is a diagram for explaining the operation of the network monitoring system according to the first embodiment when an abnormality occurs in the monitoring target device. Assume that an abnormality occurs in the monitoring target device 20 that has been operating as described with reference to FIG. 3 when diagnostic information is transmitted at intervals of x minutes. At this time, the transmission interval adjustment unit 26 returns the diagnostic information transmission interval to the minimum transmission interval of 1 minute, and the transmission unit 22 transmits diagnostic information including status information indicating the occurrence of abnormality at 1 minute intervals. In this way, by setting the transmission interval to the minimum transmission interval, the occurrence of abnormality can be quickly notified to the monitoring device 10. The transmission interval adjustment unit 26 continues transmission at a minimum transmission interval of 1 minute until the monitoring device 10 is restored and the state detection unit 24 detects that the state is normal. Thereby, it is possible to promptly notify the monitoring device 10 of the restoration of the device. On the other hand, the state determination unit 14 of the monitoring device 10 determines that an abnormality has occurred in the monitoring target device 20 based on the state information included in the received diagnostic information.

  After that, when the monitoring target device 20 is restored to a normal state, the transmission unit 22 transmits diagnostic information including state information indicating that the monitoring device 10 is normal at 1 minute intervals of the minimum transmission interval. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 has been restored to the normal state based on the state information included in the received diagnostic information. Thereafter, the transmission interval adjustment unit 26 changes the transmission interval of the diagnostic information as usual as described with reference to FIG.

  FIG. 5 is a diagram for explaining the operation of the network monitoring system according to the first embodiment when a failure occurs in the network. In the network monitoring system 100 operating normally as described with reference to FIG. 3, it is assumed that a failure has occurred in the LAN network 30 when diagnostic information is transmitted at intervals of x minutes. Since no abnormality has occurred in the monitoring target device 20, the transmission unit 22 transmits diagnostic information at intervals of x minutes. At this time, since the network failure determination unit 16 of the monitoring device 10 waits for the transmission interval (that is, x minutes) after the last reception of the diagnosis information, the diagnosis information does not arrive. It is determined that a failure has occurred in the LAN network 30 with the device 20. Thereafter, when the failure of the LAN network 30 is recovered and the diagnosis information arrives, the network failure determination unit 16 determines that the network failure has been recovered.

  The configuration and operation of the network monitoring system 100 according to the first embodiment have been described above. In the network monitoring system 100, when the monitoring target device 20 is normal, the transmission interval is extended every predetermined confirmation period. Thereby, network traffic can be reduced and the load on the network can be suppressed.

(Second Embodiment)
FIG. 6 is a diagram for explaining a network monitoring system 100 according to the second embodiment of the present invention. In the network monitoring system 100 illustrated in FIG. 6, the monitoring device 10 and the first to fourth monitoring target devices 20_1 to 20_4 are used when a failure occurs in the normal network 31 used during normal operation and the normal network 31. Connected to the detour network 32. In FIG. 6, the normal route passing through the normal network 31 is illustrated by a solid line, and the bypass route passing through the bypass network 32 is illustrated by a broken line.

  FIG. 7 is a diagram for explaining the configuration of the network monitoring system 100 according to the second embodiment. In FIG. 7, the same or corresponding components as those in FIG. 2 are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  In the present embodiment, the transmission interval adjusting unit 26, when a change occurs in the detection result of the state detecting unit 24, is applied to both the normal route passing through the normal network 31 and the detour route passing through the detour network 32 a predetermined number of times (for example, Once, diagnostic information is transmitted, and after transmitting a predetermined number of times (for example, once), the transmission unit 22 is controlled so that the diagnostic information is periodically transmitted only to the normal route. When the detection result of the state detection unit 24 changes, the state of the monitoring target device 20 changes from “normal” to “abnormal”, the state changes from “abnormal” to “normal”, and the monitoring target It includes three cases where the device 20 is activated.

  The state determination unit 14 of the monitoring device 10 determines the state of the monitoring target device 20 based on the state information included in the diagnostic information arriving from the normal route or the detour route. In other words, the state determination unit 14 considers that the state information notified from the monitoring target device 20 is valid regardless of whether the state information is a normal route or a detour route.

  Further, the network failure determination unit 16 determines the presence / absence of a failure only for the normal network 31 and does not determine the presence / absence of a failure for the bypass network 32. That is, it is determined whether only the diagnostic information received from the normal route has arrived at the notified transmission interval.

  FIG. 8 is a diagram for explaining the operation of the network monitoring system according to the second embodiment when the monitoring target device and the network are normal.

  First, immediately after the monitoring target device 20 is activated, the transmission interval adjustment unit 26 of the monitoring target device 20 sets the transmission interval of the diagnostic information to the minimum transmission interval (hereinafter referred to as 1 minute). Then, the transmission interval adjustment unit 26 controls the transmission unit 22 so that diagnostic information is transmitted a predetermined number of times (hereinafter referred to as “one time”) to both the normal route passing through the normal network 31 and the bypass route passing through the bypass network 32. To do. In FIG. 8, the diagnostic information passing through the normal route is illustrated by a solid line arrow, and the diagnostic information passing through the detour route is illustrated by a broken line arrow. After transmitting once to the normal route and the detour route, the transmission interval adjustment unit 26 controls the transmission unit 22 so that diagnostic information is periodically transmitted only to the normal route. Similar to the first embodiment, the transmission interval of diagnostic information from the normal route is extended when the monitoring target device 20 is normal for a predetermined confirmation period (for example, 3 days).

  On the other hand, the state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 is normal based on the state information included in the received diagnostic information. In the present embodiment, the diagnostic information arrives from both the normal route and the bypass route, but the determination may be made based on the diagnostic information that has passed through any route. Further, the network failure determination unit 16 predicts the reception time of the next diagnosis information based on the transmission interval information included in the diagnosed diagnosis information, and the normal network 31 if the diagnosis information is received from the normal route as predicted. Is determined to be normal.

  FIG. 9 is a diagram for explaining the operation of the network monitoring system according to the second embodiment when an abnormality occurs in the monitoring target device. It is assumed that an abnormality has occurred in the monitoring target device 20 that has been operating as described in FIG. At this time, since the detection result of the state detection unit 24 changes from “normal” to “abnormal”, the transmission interval adjustment unit 26 transmits the diagnostic information only once for both the normal route and the detour route. 22 is controlled. The diagnostic information transmitted here includes state information indicating the occurrence of an abnormality. The state determination unit 14 of the monitoring device 10 determines that an abnormality has occurred in the monitoring target device 20 based on the state information included in the received diagnostic information. Thereafter, the transmission interval adjusting unit 26 returns the diagnostic information transmission interval to 1 minute, which is the minimum transmission interval, and controls the transmitting unit 22 so that the diagnostic information is transmitted only to the normal route. The transmission interval adjustment unit 26 continues transmission at a minimum transmission interval of 1 minute until the monitoring device 10 is restored and the state detection unit 24 detects that the state is normal.

  After that, when the monitoring target device 20 is restored to the normal state, the transmission interval adjustment unit 26 changes the detection result of the state detection unit 24 from “abnormal” to “normal”, so 1 for both the normal route and the bypass route. The transmitter 22 is controlled so that the diagnostic information is transmitted only once. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 has been restored to the normal state based on the state information included in the received diagnostic information. Thereafter, the transmission unit 22 transmits diagnostic information including state information indicating that the monitoring device 10 is normal at 1 minute intervals of the minimum transmission interval, and extends the transmission interval every time the confirmation period elapses.

  FIG. 10 is a diagram for explaining the operation of the network monitoring system according to the second embodiment when a failure occurs in the network. In the network monitoring system 100 operating normally as described with reference to FIG. 8, it is assumed that a failure occurs in the normal network 31 when diagnostic information is transmitted at intervals of x minutes. At this time, the network failure determination unit 16 of the monitoring device 10 determines that a failure has occurred in the normal network 31 because diagnostic information cannot be received from the normal route. Even after a failure occurs in the normal network 31, the transmission unit 22 transmits diagnostic information at intervals of x minutes, but has not reached the monitoring device 10 due to a failure in the normal network 31. At this stage, the monitoring device 10 cannot receive diagnostic information from the normal route, but the monitoring target device 20 does not receive diagnostic information from the detour route because there is no state change, that is, no abnormality has occurred. Therefore, it can be determined that no abnormality has occurred in the monitoring target device 20 when diagnostic information does not arrive from the detour route.

  Thereafter, it is assumed that an abnormality has occurred in the monitoring target device 20. At this time, since the detection result of the state detection unit 24 changes from “normal” to “abnormal”, the transmission interval adjustment unit 26 transmits the diagnostic information only once for both the normal route and the detour route. 22 is controlled. The diagnostic information transmitted here includes state information indicating the occurrence of an abnormality. At this stage, since a failure has occurred in the normal network 31, diagnostic information reaches the monitoring device 10 only from the detour route. The state determination unit 14 of the monitoring device 10 determines that an abnormality has occurred in the monitoring target device 20 based on the state information included in the diagnostic information received from the detour route. Thus, according to the present embodiment, even when a failure occurs in the normal network 31, the state determination unit 14 of the monitoring device 10 can determine the occurrence of a failure in the monitoring target device 20 via the detour route. . During the occurrence of an abnormality, the transmission interval adjustment unit 26 returns the diagnostic information transmission interval to the minimum transmission interval of 1 minute, and controls the transmission unit 22 so that the diagnostic information is transmitted only to the normal route. The transmission interval adjustment unit 26 continues transmission at a minimum transmission interval of 1 minute until the monitoring device 10 is restored and the state detection unit 24 detects that the state is normal. At this stage, the diagnostic information cannot be received from the normal route, so the network failure determination unit 16 of the monitoring apparatus 10 determines that a failure has occurred in the normal network 31.

  Thereafter, it is assumed that the failure of the normal network 31 is recovered. At this time, since diagnostic information can be received from the normal route, the state determination unit 14 of the monitoring device 10 determines that the normal network 31 has been restored to a normal state. At this stage, since the abnormality still occurs in the monitoring target device 20, the monitoring target device 20 transmits diagnostic information indicating the abnormality, and the state determination unit 14 of the monitoring device 10 monitors the monitoring target based on the diagnostic information. It is determined that the device 20 is abnormal.

  After that, when the monitoring target device 20 is restored to the normal state, the transmission interval adjustment unit 26 changes the detection result of the state detection unit 24 from “abnormal” to “normal”, so 1 for both the normal route and the bypass route. The transmitter 22 is controlled so that the diagnostic information is transmitted only once. The state determination unit 14 of the monitoring device 10 determines that the monitoring target device 20 has been restored to the normal state based on the state information included in the received diagnostic information.

  The configuration and operation of the network monitoring system 100 according to the second embodiment have been described above. When the monitoring target device notifies the monitoring device using two routes, the normal route and the bypass route, the monitoring target device periodically transmits the same information to both routes, and is effective on the monitoring device side. A method of selecting information to be considered is conceivable. However, in this method, there is a possibility that the traffic on the bypass network increases and the load on the bypass network increases.

  On the other hand, since the network monitoring system 100 according to the present embodiment is configured to transmit diagnostic information to the bypass route a predetermined number of times (for example, once) when a state change occurs in the monitoring target device 20, traffic on the bypass route It is possible to monitor the monitoring target device 20 using two routes without increasing so much.

  Also in the present embodiment, as in the first embodiment, when the monitoring target device 20 is normal, the transmission interval of the diagnostic information to the normal route is extended every predetermined confirmation period. Thereby, the load of the normal network 31 can be suppressed.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications are possible depending on the combination of each component and each processing process, and such modifications are within the scope of the present invention. is there.

  DESCRIPTION OF SYMBOLS 10 Monitoring apparatus, 12 Receiving part, 14 State determination part, 16 Network failure determination part, 20 Monitoring object apparatus, 22 Transmission part, 24 State detection part, 26 Transmission interval adjustment part, 30 LAN network, 31 Normal network, 32 Detour network 100 Network monitoring system.

Claims (6)

A network monitoring system in which a monitoring device and a monitoring target device are connected via a network,
The device to be monitored is
A state detector that detects the state of the monitored device;
A transmission unit for transmitting status information of the monitoring target device to the monitoring device;
A transmission interval adjustment unit that adjusts an interval at which the transmission unit transmits the state information,
The monitoring device includes a state determination unit that determines a state of the monitoring target device based on state information received from the monitoring target device via a network,
The transmission interval adjustment unit increases the transmission interval of the state information than before when the monitoring target device is normal for a predetermined period after starting transmission of the state information at a certain transmission interval. A featured network monitoring system.   The network monitoring system according to claim 1, wherein the transmission interval adjustment unit repeats the process of increasing the transmission interval until the transmission interval of the state information reaches a predetermined maximum transmission interval.   3. The transmission interval adjustment unit adjusts the transmission interval of the state information to a predetermined minimum transmission interval when an abnormality of the monitoring target device is detected by the state detection unit. The network monitoring system described. The transmission unit is configured to transmit transmission interval information to the monitoring target device together with the state information,
If the next status information and transmission interval information do not arrive at a transmission interval acquired from certain transmission interval information, the monitoring target device determines that a failure has occurred in the network between the monitoring device and the monitoring target device The network monitoring system according to claim 1, further comprising a network failure determination unit. The monitoring device and the monitoring target device are connected via a normal network used during normal operation and a bypass network used when a failure occurs in the normal network,
The transmission interval adjustment unit, when a change occurs in the detection result of the state detection unit, the state information is transmitted a predetermined number of times to both a normal route passing through the normal network and a bypass route passing through the bypass network, After transmitting a predetermined number of times, the transmitter is controlled so that the state information is periodically transmitted only to the normal route,
5. The network monitoring system according to claim 1, wherein the state determination unit determines the state of the monitoring target device based on the state information arriving from the normal route or the detour route. .   The network monitoring system according to claim 5, wherein the network failure determination unit determines whether or not there is a failure with respect to the normal network.

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