JP5202376B2 - COMMUNICATION DEVICE, COMMUNICATION SYSTEM, AND COMMUNICATION CONTROL METHOD - Google Patents

Description

  The present invention relates to a communication device, a communication system, and a communication control method for transmitting and receiving a safety message in a safety network that realizes functional safety.

  A safety message transmission / reception operation in a conventional safety network will be described below. In the conventional safety network, each device grasps the operation state of the opposite device by performing safety message transmission (transmission) and safety message confirmation between safety devices. This safety message transmission / reception and confirmation operation has a response timer in preparation for the occurrence of a transmission error. The response timer is activated by transmission of a safety message, and the response timer is activated before receiving a safety message confirmation that is a response message to the transmission message. When it expires, it resends the same message. In addition, a repetitive repeat timer is prepared in case the response timer expires continuously for a predetermined number of times, and this repetitive repeat timer is activated at the first safety message transmission. When the repetitive timer expires, it is determined that a safety message transmission error has occurred and safety control is performed. Non-Patent Document 1 below provides a periodic timer that restarts every time a safety message is received on the safety message receiver side, and performs safety control when the periodic timer expires without a safety message arriving for a certain period of time. The control method to be performed is described.

  Here, the specified number of consecutive expirations of the response timer, that is, the maximum number of retransmissions can be calculated based on the bit error occurrence rate of the network, and the probability that all retransmissions will fail (safety messages will result in transmission errors and safety control will be executed). The maximum number of retransmissions can be specified so that the transmission error rate satisfies the target transmission error rate in the network. The maximum response time, which is the worst value of the response time from the signal input on the safety message transmission side to the signal output on the safety message reception side, is calculated using the maximum number of retransmissions.

"Safety Bus System for Automation" by D. Reinert and M. Schaefer, NPO Safety Engineering Laboratory, September 24, 2003, P95-98

  In a conventional safety network, communication is performed by sending a safety message and receiving a safety message confirmation as described above, and message loss continues due to a transmission error state caused by more bit errors than expected. When this occurs, a transmission error is detected and safety control is performed. Therefore, it is necessary to increase the number of retransmissions in order to perform reliable message transmission on a transmission path with a high probability of occurrence of bit errors. On the other hand, since safety control is performed when a response timer timeout occurs for the number of retransmissions, there is a problem that it takes a long time to start safety control after a transmission error occurs if the number of retransmissions is large. . There is also a problem that the maximum response time becomes a very large value.

  The present invention has been made in view of the above, and obtains a communication device, a communication system, and a communication control method for activating safety control at a high speed when a transmission error occurs and increasing the maximum response time. With the goal.

  In order to solve the above-described problems and achieve the object, the present invention provides a communication device that constitutes a safety network, including a state of a transmission path with a counterpart device that is a communication partner device, and the safety network. Based on a target transmission error rate, a retransmission number determination means for determining the number of retransmissions when transmitting a transmission frame to the opposite device, and a transmission frame having the same contents over the determined number of retransmissions to the opposite device Transmission frame retransmitting means for repeatedly transmitting.

  According to the present invention, since the transmission frame is redundantly transmitted the number of times determined according to the transmission path state, the transmission failure probability of the safety message is reduced, and the highly reliable communication is realized. When transmission fails, the failure can be determined in a short time, and safety control can be executed at high speed.

  Embodiments of a communication apparatus, a communication system, and a communication control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a first embodiment of a network device that is a communication device according to the present invention, and shows two network devices that transmit and receive a safety message in a safety network that is a communication system according to the present invention. A configuration example is shown. As shown in the figure, the configuration of each of these network devices (network devices 1-1 and 1-2) is the same, and each network device includes a periodic transmission unit 10 as a component for executing processing in the safety layer. As a component for executing processing in the transmission layer, a bit error probability acquisition unit 11, a retransmission number determination unit 12, a transmission frame retransmission unit 13, a reception frame determination unit 14, a transmission unit 15, and a reception unit 16 are provided. The network devices 1-1 and 1-2 are connected via the network transmission path 101.

  In the following, when there is no need to distinguish each network device, that is, when a common item is described for each network device, these network devices 1-1 and 1-2 are collectively referred to as network device 1. It describes.

  In the network device 1, the periodic transmission unit 10 transmits a safety message, which is a message generated and decrypted in the safety layer, at a fixed period. The bit error probability acquisition unit 11 calculates the bit error occurrence probability in the network transmission path from the opposite device to the own device. The retransmission number determination unit 12 determines the number of retransmissions based on the bit error occurrence probability calculated by the bit error probability acquisition unit 11. The transmission frame retransmission unit 13 retransmits the transmission frame by the number of retransmissions determined by the retransmission number determination unit 12. When receiving a transmission frame, the reception frame determination unit 14 performs a transmission frame determination process described later. The transmission unit 15 transmits the transmission frame to the opposite device. The receiving unit 16 receives a transmission frame transmitted from the opposite device.

  FIG. 2 is a diagram illustrating a configuration example of a transmission frame transmitted by the network device 1 on the safety network. The transmission frame includes a destination address 31, a transmission source address 32, a transmission frame length 33, a control flag 34, and the number of retransmissions. 35, a payload 36 and an error detection code 37 are included as information elements.

  Next, the overall operation of the network device 1 will be described with reference to FIGS. 1 and 2. The periodic transmission unit 10 periodically generates a safety message and requests the transmission frame retransmission unit 13 to transmit the generated safety message to the opposite device (the network device 1 of the communication partner). The transmission frame retransmission unit 13 repeatedly transmits a transmission frame (see FIG. 2) storing the safety message received from the fixed-cycle transmission unit 10 at a predetermined cycle by the number of retransmissions acquired from the retransmission number determination unit 12.

  Here, the retransmission number determination unit 12 calculates the number of retransmissions (the number of repetitions) using the bit error probability acquired from the bit error probability acquisition unit 11, and in addition to this bit error probability, Is determined so as to achieve a target safety message transmission failure probability based on the length of the range used for error detection code calculation. The calculated value is stored in the transmission frame as the number of retransmissions 35. As the error detection code 37, for example, CRC (Cyclic Redundancy Check) is used. Consider a case where the CRC calculation target is calculated as the range of the destination address 31 to the payload 36 and the result is stored in the error detection code 37. When a bit error occurs when this transmission frame is transmitted over the network, an error occurring in the CRC calculation target range, that is, the range of the destination address 31 to the payload 36 can be detected by CRC calculation on the receiving side. is there. Also, errors occurring in the range of the error detection code 37 can be detected because the CRC calculation on the receiving side is different from the content of the error detection code 37.

Now, assuming that the bit error occurrence probability of the network transmission path 101 is E and the bit length of the transmission frame is L, the probability F that this transmission frame becomes a transmission error due to the occurrence of a bit error on the network transmission path is given by It is represented by However, the power symbol “^” represents “A raised to the B power” in the case of “A ^ B”.
F = (1- (1-E) ^ L) (1)

Therefore, when a transmission frame is redundantly transmitted N times, the probability P that all redundant transmission frames cause a transmission error can be expressed by the following equation (2).
P = (F ^ N) (2)

Therefore, when the target safety message transmission failure probability is Λ, the retransmission number determination unit 12 satisfies the following expression (3) so that all redundant transmission frames are less than the safety message transmission failure probability Λ that causes a transmission error. N is determined as the number of retransmissions.
Λ <(F ^ N) (3)

  In defining a bit length of a transmission frame, it is optimal to determine the number of retransmissions as described above in a safety network that employs a fixed-length transmission frame. Also, in a safety network that employs variable-length transmission frames, the above-mentioned calculation is performed based on the maximum frame length, and the number of retransmissions is calculated, so that the safety message transmission failure probability is set to the target value for all frames. It can be kept below.

  Transmission frames repeatedly transmitted by the transmission frame retransmission unit 13 (each transmission frame storing the same safety message) are sent from the transmission unit 15 to the network transmission path 101 in time series, and are transmitted via the network transmission path 101. It is received by the receiving unit 16 of the connected opposite device (the network device 1 on the receiving side).

  In the opposite device of the network device 1 that has transmitted the transmission frame in the above procedure, when the transmission frame is received, the reception unit 16 performs error detection on the transmission frame, and if there is no error, the reception frame determination unit 14 receives the reception frame. (Received transmission frame) is passed, and the bit error probability acquisition unit 11 is notified of the reception data length (reception frame length). When an error is detected, the received data length and error information (that an error has been detected) is notified to the bit error probability acquiring unit 11 without passing the received frame to the received frame determining unit 14. Based on the received reception frame length and error information, the bit error probability acquisition unit 11 calculates a bit error occurrence probability (bit error occurrence probability in the network transmission path from the opposite device to the own device). In the network transmission path, when it is assumed that the bit error occurrence probability is greatly different for each transmission direction, the calculated bit error occurrence probability is stored in a predetermined position in the transmission frame and notified to the opposite device. Good. That is, the network devices 1 that communicate with each other may exchange the calculated bit error occurrence probability and determine the number of retransmissions based on the bit error occurrence probability received from the other party.

  The procedure for the bit error probability acquisition unit 11 to calculate the bit error occurrence probability is not particularly defined. For example, each time the received frame length is notified, the notified frame length is added (integrated). In addition, when error information is notified together with the reception frame length, the frame length added between the previous error detection and the current error detection (the frame length and the reception error of the transmission frame having no reception error) is added. The bit error occurrence probability is calculated based on the frame length obtained by adding up the frame lengths of the detected transmission frames.

  When the reception frame determination unit 14 receives the reception frame from the reception unit 16, the reception frame determination unit 14 determines whether the same reception frame as the reception frame received this time has been received in the past, and if the same reception frame has not been received in the past The safety message is extracted from the payload of the received frame received this time, and the safety message is passed to the safety layer. On the other hand, if a received frame identical to the received frame received this time has been received in the past, the received frame is discarded without being passed to the safety layer. In the case of a network configuration in which transmission frames from a plurality of transmission sources arrive together, the reception frame determination unit 14 may hold transmission frames previously received for each transmission source and use them for comparison. Good.

  Note that a sequence number area may be provided in the frame format shown in FIG. 2 and used for confirming the identity of the received frame.

  The safety layer that has received the safety message from the reception frame determination unit 14 of the transmission layer processes the safety message.

  The overall operation as described above will be described in more detail with reference to FIG. FIG. 3 is a sequence diagram illustrating a procedure when the network devices 1 according to the first embodiment exchange transmission frames in the secure network. As an example, the network device 1-1 is connected to the network device 1-2. The procedure for transmitting a transmission frame is shown. In FIG. 3, for the sake of simplicity, only the transmission operation from the network device 1-1 to the network device 1-2 is shown. However, in an actual safety network, the network device 1-2 to the network device 1- The transmission operation to 1 is also performed at the same time.

  In the safety layer of the network device 1-1, the fixed-cycle transmitter 10 generates a safety message at the set cycle timer cycle (step S1). This safety message is stored in the transmission frame by the transmission frame retransmission unit 13 in the transmission layer, and transmitted from the transmission unit 15 onto the network transmission path 101. The transmission frame in which the safety message is stored arrives at the network device 1-2, and is received and processed by the reception unit 16 and the reception frame determination unit 14 in the transmission layer. The When the safety message reception process in the safety layer is completed (normal end), a safety message reception timer is started. This reception timer is a timer for determining whether or not a safety message can be received periodically. When the next safety message reception process is completed before the timer expires, it is restarted. Is done.

  At this time, in the network device 1-1, even if the transmission frame storing the safety message does not cause a transmission error, the transmission frame retransmission unit 13 determines that the same transmission frame is the specified number of times (the number of retransmissions determined by the retransmission number determination unit 12). ) Only (steps S11 to S13). That is, the network device 1-1 always transmits a transmission frame a specified number of times without confirming delivery of the transmission frame with the network device 1-2. Note that the example of FIG. 3 shows a case where all the transmission frames transmitted in steps S11 to S13 are received by the network device 1-2 without causing a transmission error.

  On the other hand, the network device 1-2 determines the received frame from the first received transmission frame (the transmission frame transmitted in step S11) without causing a transmission error among the transmission frames arrived from the network device 1-1. The unit 14 retrieves the safety message, and the retrieved safety message is passed to the safety layer.

  As shown in the description of the overall operation performed with reference to FIG. 1 and FIG. 2, the number of retransmissions of the transmission frame is calculated so that the bit error occurrence probability, which is a safety message transmission failure probability, is suppressed to a target value or less. Even when a transmission error occurs in a part of the transmission frames, the transmission of the safety message is successful if one of the multiple transmissions can be received normally.

  FIG. 3 also shows a case where an error occurs in the transmission frame. That is, the network device 1-1 periodically transmits a safety message in a redundant transmission frame (step S1 shown in the figure and steps S11 to S13, S21 to S23, and S31 to S33 following them). For example, FIG. Even if a transmission error occurs in a part (step S21) of the redundant transmission frame transmission steps S21 to S23 when the safety message # 2 shown is transmitted, the transmission frame is transmitted to the network device in the other steps S22 and S23. The message arrives at 1-2 without error and the transmission of the safety message is successful. For example, if the same number of retransmissions is set to 5 and the same transmission frame is transmitted 5 times and the first to fourth frames are discarded due to a transmission error, if the fifth frame normally arrives at the receiving side, Safety message transmission between safety layers is successful. As in this case, the last frame of the maximum number of retransmissions arrives, and the response time when performing safety control by the safety message included in the frame becomes the maximum response time.

  As described above, in the safety network configured by the network device 1 according to the present embodiment, the message transmission side determines based on the bit error occurrence probability without executing the delivery confirmation procedure between the opposing network devices 1. A transmission frame is transmitted for the number of retransmissions. Therefore, time for executing the delivery confirmation procedure becomes unnecessary, and the maximum response time can be shortened compared to the conventional case.

  Further, as in the redundant transmission frame transmission steps S31 to S33 when the safety message # 3 shown in FIG. 3 is transmitted, factors other than EMI (Electro Magnetic Interference) of the network transmission path, for example, physical damage of the cable, etc. As a result, a state in which the bit error occurrence probability is equal to or higher than a predetermined value occurs, and all redundant transmission frames have transmission errors, and the control operation when safety message transmission fails is as follows.

  In the safety layer of the network device 1-2, the safety message arriving from the network device 1-1 is always monitored, and when the periodic reception of the safety message is interrupted, the safety control is activated and emergency brake control is performed. The time for determining periodic reception interruption is obtained from the product of the period, the retransmission time and the number of retransmissions, but the control procedure of this embodiment does not involve a delivery confirmation procedure for retransmission, so the determination time is set to be longer than the conventional method. Can be shortened.

  In the example of FIG. 3, the reception side uses a reception timer to determine periodic reception interruption, and the value of this reception timer is set to the value of the periodic timer for the retransmission time (the transmission execution time of each transmission frame to be retransmitted). (Interval) and the product of the number of retransmissions. When this reception timer expires due to the absence of a safety message, it is determined that a transmission error has occurred and safety control is activated. Note that the value of the periodic timer is predetermined by the system and is known in each network device. Further, the number of retransmissions of the transmission frame is stored as the number of retransmissions 35 of the transmission frame as shown in FIG. 2, and the value of the reception timer can be calculated using this value.

  Thus, in the safety network of the present embodiment, the network device on the transmission side of the safety message is based on the target bit error occurrence probability as not performing the delivery confirmation procedure in the transmission layer between the network devices. The transmission frame is redundantly transmitted for the calculated number of retransmissions. As a result, it is possible to reduce the probability of safety message transmission failure and realize highly reliable communication, and to determine the failure in a short time when safety message transmission fails, and to perform safety control at high speed.

  In addition, since the delivery confirmation procedure is not executed, the number of retransmissions (transmission frame transmission) necessary to ensure reliability can be performed in a short time, and as a result, the maximum response time can be shortened.

  Further, if a maximum response time comparable to the conventional one is achieved, more retransmissions can be performed within the maximum response time, so that more reliable communication can be realized.

Embodiment 2. FIG.
In the first embodiment, the case of one set of network transmission paths has been described. Next, the case of a plurality of sets of network transmission paths will be described. In the present embodiment, description will be made on the assumption that the configurations of the network devices constituting the safety network are the same.

  FIG. 4 is a diagram illustrating a configuration example of the network device according to the second embodiment. The network device 1a of the present embodiment includes a periodic transmission unit 10 that executes processing in the safety layer, a reception frame determination unit 14 that executes processing in the transmission layer, a transmission line distribution transmission unit 17, a reception alignment unit 18, and a plurality of The retransmission control unit 20 is provided. Each retransmission control unit 20 is connected to the retransmission control unit 20 of another network apparatus 1a via different network transmission paths 101, 102, or 103. In addition, the same code | symbol is attached | subjected to the same component as the network apparatus 1 of Embodiment 1, and the description is abbreviate | omitted.

  The transmission path allocation transmission unit 17 distributes the retransmission frame to a plurality of network transmission paths and transmits it. The reception alignment unit 18 aligns retransmission frames received from a plurality of network transmission paths in time series. The retransmission control unit 20 is arranged for each network transmission line, and performs retransmission control of transmission frames received from the transmission line distribution transmission unit 17 and reception control of transmission frames transmitted from other network devices.

  FIG. 5 is a diagram illustrating a configuration example of each retransmission control unit 20 provided in the network device 1a. The retransmission control unit 20 includes a bit error probability acquisition unit 11, a transmission frame retransmission unit 13, a transmission unit 15, and a reception unit 16 that are the same components as those provided in the network device 1 according to the first embodiment, and the number of retransmissions. And a determination unit 12a. Note that detailed description of components having the same reference numerals as those provided in the network device 1 of the first embodiment is omitted.

  The retransmission number determination unit 12a illustrated in FIG. 5 determines the number of retransmissions by a procedure different from the retransmission number determination unit 12 included in the network device 1 of the first embodiment. The procedure for determining the number of retransmissions will be described later.

  Next, the transmission / reception operation of the safety message by the network device 1a according to the present embodiment will be described with reference to FIG. 4 and FIG. The description of the same operation as that of the network device 1 of the first embodiment is omitted.

  In the network device 1a, the periodic transmission unit 10 periodically generates a safety message and requests the transmission path distribution transmission unit 17 to transmit the generated safety message to the opposite device. The transmission path allocation transmission unit 17 distributes the safety message received from the periodic transmission unit 10 to each retransmission control unit 20. For example, when each retransmission control unit 20 is connected to a different counterpart (network device) via a network transmission path, each safety message is distributed according to the destination. In addition, when each retransmission control unit 20 is connected to the same counterpart via a network transmission path, each safety message is distributed according to the processing load of each retransmission control unit 20 or the traffic state of the network transmission path. . In addition, when some of the retransmission control units 20 are connected to the same destination, the processing load or traffic state of the retransmission control unit 20 connected to the same destination is considered while considering the destination. The distribution process is performed accordingly.

  In each retransmission control unit 20, when a safety message is received from the transmission path distribution transmission unit 17, the transmission frame retransmission unit 13 repeats the transmission frame storing the safety message for the number of retransmissions acquired from the retransmission number determination unit 12 a. Send. The configuration of the transmission frame is the same as that used in Embodiment 1 (see FIG. 2).

  Here, the retransmission number determination procedure by the retransmission number determination unit 12a of the present embodiment will be described. Similar to the retransmission number determination unit 12 of the first embodiment, the retransmission number determination unit 12a has a bit error probability acquired from the bit error probability acquisition unit 11, and a length of a range used for error detection code calculation in a transmission frame to be transmitted. Based on the above, the number of retransmissions that can achieve the target safety message transmission failure probability is determined.

For example, if the bit error occurrence probabilities of the network transmission lines 101, 102, and 103 are E1, E2, and E3, respectively, and the bit length of the transmission frame is L, this transmission frame is considered to be a transmission error due to the occurrence of a bit error on each network transmission line. Probabilities F1, F2, and F3 are expressed by the following equation (4). However, n represents 1-3.
Fn = (1- (1-En) ^ L) (4)

Further, when a transmission frame is redundantly transmitted N1, N2, and N3 times on each network transmission path, the probability P that all redundant transmission frames cause a transmission error is expressed by the following equation (5).
P = F1 ^ N1 * F2 ^ N2 * F3 ^ N3 (5)

Therefore, when the target safety message transmission failure probability is Λ, the retransmission number determination unit 12a satisfies the following equation (6) so that all redundant transmission frames are below the safety message transmission failure probability Λ that causes a transmission error. N1, N2, and N3 are respectively determined as the number of retransmissions.
Λ <(F1 ^ N1 × F2 ^ N2 × F3 ^ N3) (6)

  In determining the number of retransmissions, each retransmission number determination unit 12 may acquire information on each retransmission control unit 20 from the transmission path distribution transmission unit 17, or each retransmission control unit 20 may mutually receive information. It may be performed by exchanging. Also, individual target transmission failure probabilities for each network transmission path may be defined in advance, and each retransmission control unit 20 may individually determine the number of retransmissions so as to achieve the target transmission failure probability. . Regardless of which method is used, it is possible to set a smaller value for the number of retransmissions per network transmission path than in the case of the first embodiment.

  In each retransmission control unit 20, the transmission frame repeatedly transmitted by the transmission frame retransmission unit 13 is transmitted from the transmission unit 15 to each network transmission path in time series, and is connected to the opposite device (reception) via each network transmission path. Is received by the receiving unit 16 of the retransmission control unit 20 in the network device 1a).

  In the opposite device of the network device 1a that has transmitted the transmission frame in the above procedure, if there is no error in the received frame, it is passed from the reception unit 16 of each retransmission control unit 20 to the reception alignment unit 18, and the reception alignment unit 18 The transmission frames received from each network transmission line are arranged in time series and passed to the reception frame determination unit 14. The subsequent processing is the same as the processing in the network device 1 of the first embodiment.

  In the present embodiment, the operation example in the case where the network device 1a is connected to three network transmission lines has been described, but the operation in the case of two or four or more is the same.

  As described above, by adopting the configuration of the network device according to the present embodiment, the number of retransmissions determined for each network transmission path can be set to a smaller value, and safety control can be executed at higher speed. . Further, if a maximum response time comparable to that of the conventional case is achieved, more retransmissions can be performed on the same band line, so that more reliable communication is possible. Further, since transmission is performed through physically different network transmission paths, communication can be continued even when some network transmission paths are physically disabled, thereby enabling more reliable communication.

  In this embodiment, an example in which a plurality of physical network transmission paths are used has been described. However, by providing a plurality of channels by frequency multiplexing on one set of network transmission paths, the same speed-up effect can be obtained. Can be obtained.

  As described above, the communication device according to the present invention is useful for a network device configuring a safety network, and is particularly suitable for realizing a safety network with higher reliability.

It is a figure which shows the structural example of Embodiment 1 of a network device. It is a figure which shows the structural example of a transmission frame. FIG. 3 is a sequence diagram showing a procedure when the network devices of the first embodiment exchange transmission frames in a secure network. 6 is a diagram illustrating a configuration example of a network device according to a second embodiment. FIG. It is a figure which shows the structural example of a resending control part.

1-1, 1-2, 1a Network device 10 Periodic transmission unit 11 Bit error probability acquisition unit 12, 12a Retransmission number determination unit 13 Transmission frame retransmission unit 14 Reception frame determination unit 15 Transmission unit 16 Reception unit 17 Transmission path distribution transmission Unit 18 reception alignment unit 20 retransmission control unit 31 destination address 32 source address 33 transmission frame length 34 control flag 35 number of retransmissions 36 payload 37 error detection code 101, 102, 103 network transmission path

Claims (10)

A communication device that constitutes a safety network that performs communication for safety control at regular intervals ,
Determination of the number of retransmissions for determining the number of retransmissions when transmitting a transmission frame to the opposite device based on the state of the transmission path with the opposite device that is the communication partner device and the target transmission error rate in the safety network Means,
Transmission frame retransmission means for repeatedly transmitting a transmission frame of the same content to the opposite apparatus for the determined number of retransmissions at regular intervals ;
A determination unit that determines the necessity of safety control based on the fixed period, the number of retransmissions, and an interval at which the transmission frame retransmission unit transmits a transmission frame of the same content;
A communication apparatus comprising:   2. The transmission frame retransmission means according to claim 1, wherein the transmission frame retransmission unit repeatedly transmits a transmission frame having the same content at a constant period without confirming whether or not each transmission frame is normally received by the opposite apparatus. Communication device. When a transmission frame is received from another communication device, it is confirmed whether a transmission frame having the same content as the transmission frame has been received, and if received, a received frame determination means for discarding the transmission frame received this time,
The communication apparatus according to claim 1, further comprising: A plurality of pairs of the retransmission number determination means and the transmission frame retransmission means, and each transmission frame retransmission means is connected to a different transmission path,
Each retransmission number determining means determines the number of retransmissions to be used by a pair of transmission frame retransmission means based on a state of each transmission path and a transmission error rate targeted in the safety network. 2. The communication device according to 2 or 3.   The communication apparatus according to claim 4, wherein the different transmission paths are channels having different wavelengths.   Bit error occurrence probability calculated based on the number of transmission frame errors detected using the error detection code included in the transmission frame received from the opposite device, and the number of bits of the received transmission frame. The communication device according to claim 1, wherein the communication device is determined by: A communication system comprising a plurality of communication devices according to any one of claims 1 to 6,
Each communication device exchanges the first number of retransmissions determined by the own device and the second number of retransmissions determined by the other communication device, and based on the obtained second number of retransmissions, the other communication A communication system, characterized by determining whether a transmission error has occurred in transmission from a device to the device itself. A communication control method executed by a communication device on the transmission side of a safety network that performs communication for safety control at a constant cycle ,
Determination of the number of retransmissions for determining the number of retransmissions when transmitting a transmission frame to the opposite device based on the state of the transmission path with the opposite device that is the communication partner device and the target transmission error rate in the safety network Steps,
A transmission frame transmission step of periodically transmitting a transmission frame of the same content at a predetermined period to the opposite device for each predetermined period, for the determined number of retransmissions,
A determination step of determining the necessity of safety control based on the fixed period, the number of retransmissions, and an interval at which the transmission frame retransmission unit transmits a transmission frame of the same content;
The communication control method characterized by including.   9. The communication control according to claim 8, wherein, in the transmission frame retransmission step, transmission frames having the same contents are repeatedly transmitted at a constant period regardless of whether each transmission frame is normally received by the opposite apparatus. Method.   Bit error occurrence probability calculated based on the number of transmission frame errors detected using the error detection code included in the transmission frame received from the opposite device, and the number of bits of the received transmission frame. The communication control method according to claim 8 or 9, characterized in that:

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