Patent Publication Number: US-2022217066-A1

Title: Information processing device, information processing system, notification method, and storage medium

Description:
TECHNICAL FIELD 
     The present invention relates to an information processing device, an information processing system, a notification method, and an information processing program. 
     RELATED ART 
     A network system constituted of a master device and a slave device is used as an industrial network system, and techniques related to the network system are known. Patent literature 1 discloses a method of suppressing a delay in establishing communication processing in a network system including a master device and a slave device. In addition, Patent literature 2 discloses a development support device for a programmable controller (PLC) system that can shorten the time required for investigating the cause of a communication abnormality when the communication abnormality occurs. 
     CITATION LIST 
     Patent Literature 
     Patent literature 1: Japanese Patent Application Laid-Open No. 2016-195329 (published on Nov. 17, 2016) 
     Patent literature 2: Japanese Patent Application Laid-Open No. 2008-181572 (published on Aug. 7, 2008) 
     SUMMARY OF INVENTION 
     Problems to be Solved 
     In the network system as described above, communication quality may be degraded or communication may be suddenly interrupted due to deterioration of a cable connecting devices, noise caused by an influence of peripheral devices, or the like. In particular, when communication is suddenly interrupted in a field network, it takes a lot of time to identify the cause or restore the network. 
     In order to address the above problems, a redundancy measure such as duplication of devices by hot standby or making a network topology ring-shaped can be taken, or cables with excellent environmental resistance that can reduce the influence of noise can be used. However, because the above-mentioned measures require significant changes to the system and are technically challenging, it is desirable to monitor the communication quality of the network system periodically without changing the current system or equipment. 
     On the other hand, when the communication quality of the network system is periodically monitored, for example, there is a problem that it takes time and effort for a user to operate a program in the master device to check for abnormalities. 
     One aspect of the present invention has been made in consideration of the above problems, and an object of the present invention is to reduce a burden on the user when monitoring the communication quality of a network system. 
     Means to Solve Problems 
     The present invention adopts the following configuration to solve the above-mentioned problems. 
     That is, an information processing device according to one aspect of the present invention includes: a statistical information acquisition unit that acquires statistical information about communication with another machine connected by a cable; an abnormality determination unit that determines an abnormality in the communication with reference to the statistical information acquired by the statistical information acquisition unit; and an abnormality notification unit that notifies a master device of a determination result from the abnormality determination unit, when the determination result indicates that the communication is abnormal. 
     In addition, the information processing system according to one aspect of the present invention is an information processing system that includes a master device and a slave device connected to the master device by a cable. The slave device includes: a statistical information acquisition unit that acquires statistical information about communication with the master device via a network; an abnormality determination unit that determines an abnormality in the communication with reference to the statistical information acquired by the statistical information acquisition unit; and an abnormality notification unit that notifies the master device of a determination result from the abnormality determination unit, when the determination result indicates that the communication is abnormal. 
     Besides, a notification method according to one aspect of the present invention is a notification method executed in an information processing device. The notification method includes: a statistical information acquisition step of acquiring statistical information about communication with another machine connected by a cable; an abnormality determination step of determining an abnormality in the communication with reference to the statistical information acquired in the statistical information acquisition step; and an abnormality notification step of notifying a master device of a determination result from the abnormality determination step, when the determination result indicates that the communication is abnormal. 
     Effects of Invention 
     According to one aspect of the present invention, the burden on the user for monitoring the communication quality of a network system can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates an example of an information processing system according to Embodiment 1. 
         FIG. 2  illustrates an example of a functional block diagram of the information processing system according to Embodiment 1. 
         FIG. 3  illustrates an example of processing procedures in the information processing device according to Embodiment 1. 
         FIG. 4  illustrates an example of a table showing statistical information according to Embodiment 1. 
         FIG. 5  illustrates an example of a display screen in a display device according to Embodiment 1. 
         FIG. 6  illustrates an example of processing procedures in the information processing device according to Embodiment 1. 
         FIG. 7  illustrates an example of a table and a graph showing statistical information according to Embodiment 1. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an embodiment according to one aspect of the present invention (hereinafter, also referred to as “the present embodiment”) is described with reference to the drawings. 
     Embodiment 1 
     § 1 Application Example 
     An information processing device according to the present embodiment is a device that functions as a slave device in a network system that performs, for example, distributed processing or the like, and is, for example, an input/output device, a sensor controller, or the like. 
     The information processing device acquires statistical information about communication with another machine connected by a cable, and determines a communication abnormality with reference to the statistical information. The information processing device is configured to transmit, when the result of the determination indicates that the communication is abnormal, information indicating the location and type of the abnormality toward a master device side of the network system. Here, the communication abnormality means, for example, a state in which frames cannot be transmitted or received normally or a state in which the transmitted or received frames are defective due to deterioration of the cable connecting the devices or noise caused by the influences of peripheral devices. In addition, the frame is a data format used in data link layer protocol such as EtherCAT or the like. 
     With the configuration described above, for example, by confirming the information transmitted to the master device when the communication abnormality is detected, the user can take appropriate measures such as changing the cable used for the connection with another machine to a cable having improved environmental performance such as noise resistance or the like. In addition, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     § 2 Configuration Example 
     [Hardware Configuration] 
     &lt;Information Processing System&gt; 
     Next, an example of a hardware configuration of the information processing system according to the present embodiment is described with reference to  FIGS. 1 and 2 .  FIG. 1  schematically illustrates an example of a hardware configuration of an information processing system  1  according to the present embodiment. In addition,  FIG. 2  is a functional block diagram of the information processing system  1  shown in  FIG. 1 . 
     As shown in  FIGS. 1 and 2 , the information processing system  1  according to the present embodiment includes a master device  10 , a plurality of slave devices (information processing devices)  20   a ,  20   b , and  20   c , and a display device  30 . In addition, each device is daisy-chained by cables. 
     Moreover, in the present specification, a case is described in which the network system constituted by the information processing system  1  is an EtherCAT (registered trademark) standard network system, but the present invention is not limited thereto. The network system may also be, for example, a network system based on standards such as Mechatronic Link (registered trademark), EtherNet/IP, CC-Link (registered trademark), or the like. In addition, the network system constituted by the information processing system  1  may be, for example, a field network system constituted by a group of manufacturing devices in a factory. Additionally, the master device may be, for example, a device such as a programmable logic controller (PLC) or the like. Besides, in the following description, if there is no particular distinction among the slave devices  20   a ,  20   b , and  20   c , any one of them may be referred to simply as slave device  20 . Moreover, in the information processing system  1  shown in  FIGS. 1 and 2 , three slave devices  20  are connected to the master device  10 , but one or two, or four or more slave devices  20  may also be connected to the master device  10 . 
     The master device  10  includes a control unit  110  and a communication unit  120 . The control unit  110  is a control device that controls the entire master device  10  and also functions as a communication control unit  111 . 
     In addition, the control unit  110  includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and the like, and controls each component according to information processing. Additionally, the same applies to a control unit  210  described later. 
     The communication control unit  111  performs control relating to the control of communication processing performed by the communication unit  120 . The communication unit  120  performs communication processing with the slave device  20 , the display device  30 , and the like. In addition, the master device  10  may include a memory (storage unit) which is not shown. 
     The slave device  20  includes the control unit  210 , a communication unit  220 , and a storage unit  230 . The control unit  210  is a control device that controls the entire slave device  20  and also functions as a statistical information acquisition unit  211 , an abnormality determination unit  212 , an abnormality notification unit  213 , and a communication processing unit  214 . 
     The statistical information acquisition unit  211  acquires statistical information about communication with another machine connected by a cable. Here, the statistical information may include information that is referred to as “statistics” in EtherNet. In addition, a detailed example of the statistical information is described later. The abnormality determination unit  212  determines whether or not there is a communication abnormality with reference to the statistical information. When a determination result obtained by the abnormality determination unit  212  indicates that the communication is abnormal, the abnormality notification unit  213  notifies the device on the master device  10  side of the determination result. The communication processing unit  214  performs control relating to the control of communication processing performed by the communication unit  220 . 
     The communication unit  220  performs communication processing with the master device  10  and other slave devices  20 . The storage unit  230  is a storage device that stores various information such as statistical information or the like. The display device  30  is a device provided with a display capable of displaying a moving image, or the display itself, such as a personal computer or the like. Moreover, as another aspect, the master device  10  may be configured to include the display device  30 , or the display device  30  may be configured to be arranged outside the information processing system  1 . In addition, the information processing system  1  shown in  FIGS. 1 and 2  has, but is not limited to, a daisy chain type configuration, and may have, for example, a ring topology type configuration. 
     § 3 Operation Example 1 
     [Information Processing System] 
     Next, a first operation example of the information processing system  1  is described with reference to  FIG. 3 .  FIG. 3  is a flowchart illustrating an example of processing procedures in the slave device  20 . In addition, the slave device  20  repeatedly executes the processing based on the flowchart in  FIG. 3  in parallel with normal control operations that should be processed by the slave device  20 . Note that, the processing procedure described below is only an example, and each processing may be changed as much as possible. In addition, with respect to the processing procedures described below, steps may be omitted, replaced, and added as appropriate according to the embodiment. 
     (Step S 101 ) 
     In step S 101 , the control unit  210  determines whether or not a predetermined unit time has elapsed since the statistical information acquisition unit  211  acquired previous statistical information. If the control unit  210  determines that the predetermined unit time has elapsed, processing of step S 102  is subsequently executed, and if the control unit  210  determines that the predetermined unit time has not elapsed, the determination processing in step S 101  is continued. Further, for example, if the statistical information acquisition unit  211  has not yet acquired statistical information since the slave device  20  was started, that is, if the determination processing in step S 101  is performed for the first time, the processing of step S 102  may be subsequently performed. In addition, the statistical information may be stored in the storage unit  230  at any time after the result of communication is reflected by the control unit  210 . 
     (Step S 102 ) 
     In the next step S 102 , the statistical information acquisition unit  211  acquires as statistical information, for example, a total number of link-off counts since the slave device  20  was started. Here, the link-off count means the number of times that the frames meant to be received by the device are not received. In addition, the statistical information acquisition unit  211  calculates the link-off count in the latest unit time by subtracting the total number of link-off counts obtained in the previous time from the total number of link-off counts obtained this time in step S 102 . 
       FIG. 4  illustrates an example of a table in which the number of frames received normally and the link-off count are aggregated on an hourly basis. For example, the row with the date and time “10:00 AM” indicates that the slave device  20  normally received 99 frames in one hour from 10:00 AM and one frame could not be received normally. 
     (Step S 103 ) 
     In the next step S 103 , the abnormality determination unit  212  determines whether a ratio of, with respect to the link-off count in a unit time, the link-off count in a unit time immediately before the above unit time is equal to or less than a first threshold value. Assuming that the latest unit time is T and the immediately preceding unit time is T−1, the value of the above ratio is expressed by the following formula. 
     
       
         
           
             
               
                 
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     In addition, the first threshold value is not limited to a specific value, and may be, for example, 1. If the value of a is equal to or less than the first threshold value, the abnormality determination unit  212  determines that an abnormality has occurred in the cable, and the abnormality notification unit  213  subsequently executes processing of step S 104 . If the value of a is greater than the first threshold value, the abnormality determination unit  212  determines that no abnormality has occurred in the cable and the control unit  210  subsequently executes processing of step S 105 . 
     (Step S 104 ) 
     In the next step S 104 , the abnormality notification unit  213  transmits, to the master device  10 , information indicating that an abnormality has occurred in the communication due to an abnormality in the cable via another slave device  20  as appropriate. In addition, the master device  10  transmits the received information to the display device  30 . 
     (Step S 105 ) 
     In the next step S 105 , the control unit  210  updates the information stored in the storage unit  230 , that is, the information indicating the total number of link-off counts and the link-off count in the last unit time. Specifically, the control unit  210  overwrites the total number of link-off counts obtained in the previous time with the total number of link-off counts obtained by the statistical information acquisition unit  211  in the last time. In addition, the control unit  210  overwrites the link-off count in the previous unit time with the link-off count in the last unit time. 
     [Example of Abnormality Notification] 
     Next, a display example of information indicating a communication abnormality is described with reference to  FIG. 5 .  FIG. 5  illustrates an example of a screen displayed by the display device  30 , which displays information about the communication. 
     In (A) of  FIG. 5 , the item “Criticality” indicates the amount or urgency of a problem indicated by a target information. The item “Source” is information indicating in which network the communication abnormality occurred. The item “Source details” is information indicating which device the communication abnormality is related to in the network in which the communication abnormality has occurred. The item “Event name” is information indicating the type of the communication abnormality. The item “Event code” is information for uniquely identifying an event about the communication abnormality. In addition, the item “Detailed information” is information corresponding to the currently selected event, and indicates the details of the event, special notes, measures recommended to the user, or the like. 
     In addition, in (B) of  FIG. 5 , the master device  10 , the slave device  20 , and cables connecting each device are illustrated. Specifically, an object  40  indicates the master device  10 . An object  41  indicates the slave device  20 . An object  42  indicates the cable connecting each device. In addition, a text  43  is information for uniquely identifying the corresponding slave device  20 . An object  44  indicates a state of the corresponding cable depending on the difference in the display mode of the object  42  such as the color or the like. As a specific example, the cable connecting the slave device  20  of “E002” and the slave device  20  of “E003” is in a state of “Warning”. 
     In the object  44 , “Normal” means that there is no communication abnormality caused by a target cable. “Warning” indicates that the number of times of a communication abnormality detected in the target cable is equal to or less than a predetermined number of times. In addition, the predetermined number of times may be, for example, once or several times. “Abnormal” indicates that the number of times of a communication abnormality detected in the target cable is greater than the predetermined number of times. A button  45  is, for example, a button for displaying a screen shown in (A) of  FIG. 5 . According to a screen example shown in (B) of  FIG. 5 , the information indicating in which cable the communication abnormality has occurred is displayed in a visually easy-to-understand manner, so that the user can easily grasp the information. 
     Operation and Effect 
     As described above, in the present embodiment, in step S 103 , the abnormality determination unit  212  determines the communication abnormality with reference to the statistical information about the link-off count, thereby eliminating the need for a user operation on the master device  10  for obtaining the information indicating the presence or absence of the communication abnormality each time. In addition, in step S 104 , the abnormality notification unit  213  transmits, to the master device  10  side, information indicating that an abnormality has occurred in the communication due to a cable abnormality, thereby enabling centralized management of the information indicating the communication abnormality in the master device  10 . Because the location of the communication abnormality caused by the faulty cable is automatically detected and notified, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     § 4 Operation Example 2 
     [Information Processing System] 
     Next, a second operation example of the information processing system  1  is described with reference to  FIGS. 6 and 7 .  FIG. 6  is a flowchart illustrating an example of processing procedures of the slave device  20 . In addition, the slave device  20  repeatedly executes the processing based on the flowchart in  FIG. 6  in parallel with the normal control operations that should be processed by the slave device  20 . 
     (Step S 101 ) 
     In step S 101 , the control unit  210  performs the same processing as in operation example 1. Moreover, if the control unit  210  determines that a predetermined unit time has elapsed since the statistical information acquisition unit  211  acquired the previous statistical information, or if, for example, the determination processing in step S 101  is performed for the first time after the slave device  20  is started, the processing of step S 202  is subsequently performed. 
     (Step S 202 ) 
     In the next step S 202 , the statistical information acquisition unit  211  acquires as statistical information, for example, the total number of invalid frames since the slave device  20  was started. Here, the invalid frame is, for example, a frame corresponding to any of the following, and a frame having any abnormality.
         Abnormality related to data link layer   FCS Check Sum mismatch   Incorrect Start Frame Delimiter   Presence or absence of Preamble   Abnormality related to physical layer   Abnormality in Manchester code   Abnormality in 4B/5B code   Short frame   Frame exceeding maximum length       

     In addition, the statistical information acquisition unit  211  calculates the number of invalid frames in the latest unit time by subtracting the total number of invalid frames obtained in the previous time from the total number of invalid frames obtained this time in step S 202 . Here, the number of invalid frames in the latest unit time can also be referred to as an increase in the number from the number of invalid frames obtained in the previous time. However, the first invalid frame that occurred in each unit time may not be counted in the increase number as it is considered to be unreliable. 
     (A) of  FIG. 7  shows an example of a table in which the number of normally received frames, the link-off count, and the number of invalid frames are aggregated on an hourly basis. For example, the row with the date and time “2:00 PM” indicates that the slave device  20  received 100 frames in one hour from 2:00 PM, and one of those frames was an invalid frame. In addition, the link-off and the reception of the invalid frame can be regarded as an abnormal frame reception. In other words, (A) of  FIG. 7  shows that the statistical information includes the number of normal frames which is the number of normal frame receptions, and the number of abnormal frames which is the number of abnormal frame receptions. 
     (Step S 203 ) 
     In the next step S 203 , the abnormality determination unit  212  determines whether or not the value of the Poisson distribution formula, which uses an increase in the number of the invalid frames as a random variable value and uses a time average of the total number of the invalid frames as a parameter, is equal to or less than a second threshold value. In addition, the Poisson distribution formula is as follows. 
     
       
         
           
             
               
                 
                   
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     Here, the parameter  2  is a value calculated by dividing the total number of the invalid frames by a cumulative operating time. That is,  2  is a time average of the total number of the invalid frames. A value k corresponding to a random variable X is an increase in the number of the invalid frames. e is the base of natural logarithms. In addition, the second threshold value is not limited to a specific value, and may be, for example, 0.25. Additionally, the value of the Poisson distribution formula equal to or less than 0.25 means that the probability of occurrence of an event is a low probability, which is equal to or less than 25%. 
     If the value of 13 of the Poisson distribution formula is equal to or less than the second threshold value, the abnormality determination unit  212  determines that a communication abnormality due to the influence of noise has occurred, and the abnormality notification unit  213  subsequently executes processing of step S 204 . If the value of 13 is greater than the second threshold value, the abnormality determination unit  212  determines that no communication abnormality due to the influence of noise has occurred, and the control unit  210  subsequently executes processing of step S 205 . 
     (Step S 204 ) 
     In the next step S 204 , the abnormality notification unit  213  transmits, to the master device  10 , information indicating that an abnormality has occurred in the communication due to the influence of noise via another slave device  20  as appropriate. In addition, the master device  10  transmits the received information to the display device  30 . 
     (Step S 205 ) 
     In the next step S 205 , the control unit  210  updates the information stored in the storage unit  230 , that is, the information indicating the cumulative operating time and the information indicating the total number of the invalid frames. With respect to the latter, specifically, the control unit  210  overwrites the previous total number of the invalid frames with the total number of the invalid frames obtained by the statistical information acquisition unit  211  in the last time. 
     Operation and Effect 
     As described above, in the present embodiment, in step S 203 , the abnormality determination unit  212  determines the communication abnormality with reference to the statistical information about the invalid frames, thereby eliminating the need for a user operation on the master device  10  for obtaining the information indicating the presence or absence of the communication abnormality each time. In addition, in step S 204 , the abnormality notification unit  213  transmits, to the master device  10  side, information indicating that an abnormality has occurred in the communication due to the influence of noise, thereby enabling centralized management of the information indicating the communication abnormality in the master device  10 . Because the location of the communication abnormality caused by the influence of noise is automatically detected and notified, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     In addition, (B) of  FIG. 7  is a graph corresponding to the table in (A) of  FIG. 7 . In the above graph, line  50  corresponds to the total number of link-off counts, and line  51  corresponds to the total number of the invalid frames. (A) of  FIG. 7  and a location  53  in (B) of  FIG. 7  show that the link-off occurred six times in one hour from 11:00 AM. It is considered that many link-offs occurred temporarily due to an abnormality in the cable or an influence of sudden noise. The steps based on the flowchart in  FIG. 6  also contribute to the understanding of the user that the link-offs were caused by the influence of noise. 
     Variation Example of Embodiment 1 
     With respect to operation example 2, the statistical information does not need to include the total number of the invalid frames of all the types described in step S 202 , and may include the total number of the invalid frames of at least one type. For example, the statistical information includes the number of short frames and the number of frames over the maximum length, that is, the number of frames having a length that exceeds the maximum length. The abnormality determination unit  212  may be configured to determine that the communication is abnormal due to noise, when the value of the Poisson distribution formula, which uses an increase in the number of the short frames and the frames over the maximum length as a random variable value and uses a time average of the total number of the short frames and the frames over the maximum length as a parameter, is equal to or less than the second threshold value. 
     In addition, with respect to the determination processing in step S 203 , the abnormality determination unit  212  may determine that the communication is abnormal when the number of the abnormal frames in a unit time exceeds a predetermined threshold value. Accordingly, the presence or absence of a communication abnormality can be determined based on the number of the abnormal frames in a unit time. 
     In addition, in operation example 1 described above, an example has been described in which determination on the abnormality in the cable is made based on the ratio of the number of occurrences of the communication abnormality (the link-off count) in continuous unit times, and in operation example 2, an example has been described in which determination on the influence of noise is made based on the value of the Poisson distribution which uses the increase number of the communication abnormality (the increase number of the invalid frames) as the random variable value. The above description does not mean that the presence or absence of the abnormality in the cable or the like is required to be determined by the number of occurrences of the communication abnormality in a unit time or the ratio thereof. Also, the above description does not mean that the presence or absence of the abnormality due to the influence of noise is required to be determined based on the value of the Poisson distribution. 
     For example, the presence or absence of an abnormality in the cable or the like may be determined based on the value of the Poisson distribution using the link-off count, or the influence of noise may be determined based on the number of the invalid frames in a unit time or the ratio thereof. 
     In addition, the present invention is not limited to a configuration in which the statistical information is stored in the slave device  20 , and may also adopt a configuration in which the master device  10  acquires and stores the statistical information from the slave device  20 . In the latter configuration, the control unit  110  of the master device  10  may include the statistical information acquisition unit  211  and the abnormality determination unit  212  and perform the same processing. 
     Embodiment 2 
     A second embodiment of the present invention is described. It should be noted that, for convenience of description, the members having the same functions as the members described in the above embodiment are designated by the same reference signs, and duplicated description of the matters already described is not repeated. In the present embodiment, description is given on a first configuration in which the user sets a desired first threshold value. After that, description is given on a second configuration in which the user sets a desired second threshold value. 
     A slave device (information processing device)  20  according to the first configuration has a configuration in which the control unit  210  further includes a first user input acquisition unit and a first threshold value setting unit from the configuration shown in  FIG. 2 . The first user input acquisition unit acquires a user input related to setting of the first threshold value. The first threshold value setting unit sets the first threshold value with reference to the user input acquired by the first user input acquisition unit. 
     The slave device  20  according to the first configuration sets the first threshold value in the following steps. 
     (1) The first user input acquisition unit acquires information indicating the first threshold value to be set, which is input by the user. Moreover, the source of the information may be the slave device  20  or the master device  10 . In other words, the user may input the information to the target slave device  20  or to the master device  10 . In the latter case, the first user input acquisition unit acquires the information via the communication unit  220 . 
     Further, the information input by the user is not limited to an absolute value of the first threshold value, and may also be a coefficient that sets a magnification from the current first threshold value or a magnification from an automatically calculated first threshold value. In the above case, for example, when the input coefficient is less than 1, it becomes difficult to detect a communication abnormality in the slave device  20 . In particular, when the coefficient is 0, it is substantially impossible to detect a communication abnormality. In addition, when the input coefficient is greater than 1, the communication abnormality can be easily detected in the slave device  20 . 
     (2) The first threshold value setting unit updates the information stored in the storage unit  230  that indicates the first threshold value with the information obtained by the first user input acquisition unit in (1). 
     According to the first configuration, the first threshold value can be set to a value desired by the user. Moreover, the first threshold values set in each slave device  20  may be different from each other, and the same applies to the second threshold value. 
     Next, description is given on the second configuration in which the user sets the desired second threshold value. The control unit  210  of the slave device  20  according to the second configuration further includes a second user input acquisition unit and a second threshold value setting unit from the configuration shown in  FIG. 2 . The second user input acquisition unit acquires a user input related to setting of the second threshold value. The second threshold value setting unit sets the second threshold value with reference to the user input acquired by the second user input acquisition unit. 
     In addition, the procedures for setting the second threshold value by the slave device  20  according to the second configuration are the same as the procedures for setting the first threshold value by the slave device  20  according to the first configuration except that the “first threshold value” is replaced with the “second threshold value”, the “first user input acquisition unit” is replaced with the “second user input acquisition unit”, and the “first threshold value setting unit” is replaced with the “second threshold value setting unit”. According to the second configuration, the second threshold value can be set to a value desired by the user. 
     In addition, the configuration may be such that the user can set the desired first threshold value and the second threshold value at the same time. In this configuration, the control unit  210  further includes the first user input acquisition unit, the first threshold value setting unit, the second user input acquisition unit, and the second threshold value setting unit from the configuration shown in  FIG. 2 . 
     SUMMARY 
     The information processing device  20  ( 20   a ,  20   b ,  20   c ) according to one aspect of the present invention includes: the statistical information acquisition unit  211  that acquires statistical information about communication with another machine connected by a cable; the abnormality determination unit  212  that determines an abnormality in the communication with reference to the statistical information acquired by the statistical information acquisition unit  211 ; and the abnormality notification unit  213  that notifies the master device  10  of a determination result from the abnormality determination unit  212 , when the determination result indicates that the communication is abnormal. The above configuration does not require a user operation on the master device  10  for obtaining information indicating the presence or absence of a communication abnormality each time. In addition, the master device  10  can centrally manage the information indicating the communication abnormality that has occurred in the network system. Therefore, according to the above configuration, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     In the information processing device  20  according to the above aspect, the statistical information may include a number of normal frames which is a number of normal frame receptions, and a number of abnormal frames which is a number of abnormal frame receptions. According to this configuration, it is possible to determine the communication abnormality with reference to the number of normal frames and the number of abnormal frames. 
     In the information processing device  20  according to the above aspect, the abnormality determination unit  212  may determine that the communication is abnormal when the number of abnormal frames within a predetermined unit time exceeds a predetermined threshold value. According to this configuration, the presence or absence of a communication abnormality can be determined based on the number of invalid frames within a predetermined unit time. 
     In the information processing device  20  according to the above aspect, the statistical information includes the link-off count, and when a ratio of a link-off count in a unit time immediately before one unit time to a link-off count in the one unit time is equal to or less than the first threshold value, the abnormality determination unit  212  determines that the communication is abnormal due to a cable abnormality. According to this configuration, a communication abnormality due to the faulty cable can be detected. 
     The information processing device  20  according to the above aspect may include a first user input acquisition unit for acquiring a user input related to setting of the first threshold value, and a first threshold value setting unit for setting the first threshold value with reference to the user input acquired by the first user input acquisition unit. According to this configuration, the first threshold value can be set to a value desired by the user. 
     In the information processing device  20  according to the above aspect, the statistical information includes a number of short frames and a number of frames over a maximum length. The abnormality determination unit  212  may determine that the communication is abnormal due to noise, when a value of a Poisson distribution formula is less than a second threshold value with an increase in the number of short frames and the number of frames over the maximum length being a random variable value, and a time average of a total number of the number of short frames and the number of frames over the maximum length being a parameter. According to this configuration, a communication abnormality due to noise can be detected. 
     The information processing device  20  according to the above aspect may include a second user input acquisition unit for acquiring a user input related to setting of the second threshold value, and a second threshold value setting unit for setting the second threshold value with reference to the user input acquired by the second user input acquisition unit. According to this configuration, the second threshold value can be set to a value desired by the user. 
     In addition, the information processing system  1  according to one aspect of the present invention includes the master device  10  and the slave devices  20  ( 20   a ,  20   b ,  20   c ) connected to the master device  10  by a cable. The slave device  20  includes: the statistical information acquisition unit  211  that acquires statistical information about the communication with the master device  10  via a network; the abnormality determination unit  212  that determines an abnormality in the communication with reference to the statistical information acquired by the statistical information acquisition unit  211 ; and the abnormality notification unit  213  that notifies the master device  10  of a determination result from the abnormality determination unit  212 , when the determination result indicates that the communication is abnormal. The above configuration does not require an operation on the master device  10  for obtaining information indicating the presence or absence of a communication abnormality each time. Therefore, according to the above configuration, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     In addition, a notification method according to one aspect of the present invention is a notification method executed in the information processing device  20 . The notification method includes: a statistical information acquisition step of acquiring statistical information about communication with another machine connected by a cable; an abnormality determination step of determining an abnormality in the communication with reference to the statistical information acquired in the statistical information acquisition step; and an abnormality notification step of notifying the master device  10  of a determination result from the abnormality determination step, when the determination result indicates that the communication is abnormal. According to this configuration, the burden on the user for monitoring the communication quality of the network system can be reduced. 
     Further, an information processing program according to one aspect of the present invention is an information processing program for causing a computer to function as the information processing device  20  described in any one of the above. The information processing program causes the computer to function as the statistical information acquisition unit  211 , the abnormality determination unit  212 , and the abnormality notification unit  213 . According to this configuration, the same effect as that of the information processing device  20  according to one aspect of the present invention can be obtained. 
     Example of Implementation by Software 
     The control blocks of the slave device  20  (in particular, the statistical information acquisition unit  211 , the abnormality determination unit  212 , the abnormality notification unit  213 , and the communication processing unit  214 ) and the control blocks of the master device  10  (in particular, the communication control unit  111 ) may be implemented by a logic circuit (hardware) formed in an integrated circuit (an IC chip) or the like, or may be implemented by software. 
     In the latter case, the slave device  20  or the master device  10  includes a computer that executes instructions of a program being software that implements each function. This computer includes, for example, one or more processors and a computer-readable recording medium that stores the program. Besides, in the computer, the processor reads the program from the recording medium and executes the program, and thereby the object of the present invention is achieved. The processor may be, for example, a central processing unit (CPU). The recording medium may be a “non-temporary tangible medium”, such as a read only memory (ROM), as well as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like. In addition, the recording medium may further include a random access memory (RAM) or the like that deploys the above program. Additionally, the above program may be supplied to the computer via any transmission medium capable of transmitting the program (communication network, broadcast wave, or the like). Further, one aspect of the present invention may also be implemented in a form of a data signal embedded in a carrier wave, in which the above program is embodied by electronic transmission. 
     The present invention is not limited to the above-described embodiments, various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining the technical means respectively disclosed in different embodiments are also included in the technical scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  information processing system 
               10  master device 
               20 ,  20   a ,  20   b ,  20   c  slave device (information processing device) 
               30  display device 
               110 ,  210  control unit 
               111  communication control unit 
               120 ,  220  communication unit 
               211  statistical information acquisition unit 
               212  abnormality determination unit 
               213  abnormality notification unit 
               214  communication processing unit 
               230  storage unit