Communication device, communication network system, and communication method

Abstract

To provide a communication device capable of transmitting a message including an appropriate freshness value even when reading of upper digits of a freshness value fails.SOLUTION: A transmitting device 10, which is a communication device that transmits a message, transmits the message containing a freshness value consisting of upper digits that are incremented each time the device is started and lower digits that are incremented each time a message is sent. A receiving device 20, which is a communication device that receives a message, accepts the message on the condition that the freshness value contained in the received message is greater than freshness values stored in the device. When failing to read the upper digits upon startup, the transmitting device 10 transmits a first message containing the freshness value that is a maximum value. Then, after the first message, the transmitting device 10 transmits a second message containing a freshness value greater than or equal to a minimum value and less than the maximum value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a communication device, a communication network system, and a communication method. [Background technology]

[0002] Patent Document 1 describes a communication network system. The communication network system is made up of a plurality of communication devices. In the communication network system, the communication devices exchange messages with each other.

[0003] When a communication device exchanges messages with another communication device, the device that sends the message sends a message that includes a freshness value. The freshness value consists of a high-order digit that is incremented each time the communication device is started, and a low-order digit that is incremented each time a message is sent.

[0004] In message exchange between communication devices, a communication device that receives a message from another communication device checks the freshness value included in the message. If the received freshness value is greater than the freshness value included in messages that have been accepted up to that point, the communication device accepts the message. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-169829 Summary of the Invention [Problem to be solved by the invention]

[0006] When a communication device starts up, it reads the most significant digits stored when the device was stopped in order to count up the most significant digits of the freshness value. At this time, the communication device may fail to read the most significant digits. In this case, the communication device is unable to assign an appropriate freshness value to a message. Therefore, while the communication device is unable to read the most significant digits, it is unable to send a message containing an appropriate freshness value to another communication device. [Means for solving the problem]

[0007] A communication device for solving the above problem is a sending-side communication device that transmits a message in a communication network system. The communication network system is composed of multiple communication devices. In message exchange between the communication devices in the communication network system, the sending-side communication device transmits a message containing a freshness value within a predetermined range, the freshness value being composed of upper digits that are incremented each time the communication device is started and lower digits that are incremented each time the message is sent. In message exchange between the communication devices in the communication network system, a receiving-side communication device that receives the message accepts the message on the condition that the freshness value included in the received message is greater than the freshness value it has stored. The receiving-side communication device also stores the freshness value included in the accepted message. When the receiving-side communication device receives a message containing the maximum freshness value, it accepts a message received after the message containing the freshness value that is less than the maximum freshness value. The sending-side communication device includes a processing device. When the sending-side communication device fails to read the upper digits at startup, the processing device executes sending a first message containing the maximum freshness value. The processing device then transmits, after the first message, a second message including the freshness value that is equal to or greater than a minimum value and less than a maximum value.

[0008] A communication network system for solving the above problem is composed of multiple communication devices. In message exchange between the communication devices in the communication network system, a sending communication device that sends a message transmits the message containing a freshness value within a predetermined range, the freshness value being configured by a high-order digit that is incremented each time the communication device is started and a low-order digit that is incremented each time the message is sent. In message exchange between the communication devices in the communication network system, a receiving communication device that receives the message accepts the message on the condition that the freshness value included in the received message is greater than the freshness value it has stored. The receiving communication device also stores the freshness value included in the accepted message. When the receiving communication device receives a message containing the maximum freshness value, it accepts a message received after the message containing the freshness value less than the maximum freshness value. In the communication network system, the sending communication device transmits a first message containing the maximum freshness value when it fails to read the high-order digit at startup. In the communication network system, the transmitting communication device transmits, after the first message, a second message including the freshness value that is equal to or greater than a minimum value and less than a maximum value.

[0009] A communication method for solving the above problem is applied to a sending communication device that transmits a message in a communication network system. The communication network system is composed of multiple communication devices. In message exchange between the communication devices in the communication network system, a sending communication device transmits a message containing a freshness value within a predetermined range, the freshness value being composed of a high-order digit that is incremented each time the communication device is started and a low-order digit that is incremented each time the message is sent. In message exchange between the communication devices in the communication network system, a receiving communication device that receives the message accepts the message on the condition that the freshness value included in the received message is greater than the freshness value it has stored. The receiving communication device also stores the freshness value included in the accepted message. Then, when the receiving communication device receives a message containing the maximum freshness value, it accepts a message received after the message containing the freshness value that is less than the maximum freshness value. The communication method includes a step in which the sending communication device transmits a first message containing the maximum freshness value when the sending communication device fails to read the high-order digit at startup. The communication method includes a step in which the communication device on the sending side transmits, after the first message, a second message including the freshness value that is equal to or greater than a minimum value and less than a maximum value. [Effects of the Invention]

[0010] The communication device, the communication network system, and the communication method can transmit a message including an appropriate freshness value even if reading of the upper digits of the freshness value fails. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a communication network system including a communication device according to an embodiment. [Figure 2]FIG. 2 is an explanatory diagram illustrating a freshness value included in a message transmitted by a communication device according to the embodiment. [Figure 3] FIG. 3 is a sequence diagram showing a mode of communication in the communication network system when the communication device of the embodiment has successfully read the upper digits of the freshness value. [Figure 4] FIG. 4 is a sequence diagram showing a mode of communication in the communication network system when the communication device of the embodiment fails to read the upper digits of the freshness value. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of a communication device will be described below with reference to FIGS. <Configuration of communication network system 100> 1, a communication network system 100 is configured with a plurality of communication devices. Specifically, the communication network system 100 includes a transmitting device 10 and a receiving device 20 as communication devices. The communication network system 100 is applied to, for example, a vehicle. The transmitting device 10 and the receiving device 20 in the communication network system 100 are, for example, electronic control devices provided in the vehicle.

[0013] 1, a transmitting device 10 and a receiving device 20 are connected via a communication bus 30. The transmitting device 10 transmits a message to the receiving device 20 via the communication bus 30. In other words, the transmitting device 10 is a transmitting-side communication device that transmits a message in a message exchange between communication devices. On the other hand, the receiving device 20 is a receiving-side communication device that receives a message in a message exchange between communication devices.

[0014] 1, the transmission device 10 includes a processing device 11 and a storage device 12. A program is stored in the storage device 12. The processing device 11 executes the program stored in the storage device 12 to perform various processes. The processing device 11 includes a processor.

[0015] 1, the receiving device 20 includes a processing device 21 and a storage device 22. A program is stored in the storage device 22. The processing device 21 executes the program stored in the storage device 22 to perform various processes. The processing device 21 includes a processor.

[0016] <Outline of freshness value> The sending device 10 sends a message including a freshness value to the receiving device 20. Fig. 2 shows the freshness value included in the message sent by the sending device 10.

[0017] As shown in Figure 2, the freshness value is composed of upper and lower digits. 2, the sending device 10 counts up the most significant digits of the freshness value when it is started up. That is, the most significant digits of the freshness value are counted up every time the sending device 10 is started up.

[0018] 2, the sending device 10 counts up the lowest digit of the freshness value when sending a message. That is, the lowest digit of the freshness value is counted up every time the sending device 10 sends a message.

[0019] 2, the sending device 10 resets the least significant digit of the freshness value when it is started up, that is, the least significant digit of the freshness value is reset every time the sending device 10 is started up.

[0020] The freshness value is formed by combining the most significant digits and the least significant digits. For example, as shown in the bottom of Figure 2, if the most significant digits are "0002" and the least significant digits are "000001", the freshness value included in the message is "0002000001".

[0021] The freshness value increases as the upper digits increase. Furthermore, when the upper digits are the same, the freshness value increases as the lower digits increase. In communication network system 100, the minimum value of the upper digits is "0001" and the maximum value is "9999". In communication network system 100, the minimum value of the lower digits is "000000" and the maximum value is "999999". Therefore, in communication network system 100, the minimum freshness value is "0001000000". Furthermore, in communication network system 100, the maximum freshness value is "9999999999". In this way, there is a predetermined range for the freshness value.

[0022] <Communication flow when the transmitter 10 successfully reads the upper digits> 3 and 4 show communication modes in the communication network system 100. In Fig. 3 and 4, the processing performed by the transmitting device 10 is executed by a processing device 11. Also, in Fig. 3 and 4, the processing performed by the receiving device 20 is executed by a processing device 21.

[0023] As described above, the most significant digits of the freshness value are counted up each time the transmitting device 10 is started up. Therefore, when the transmitting device 10 stops operating, it stores the most significant digits of the freshness value included in the message it was sending in the storage device 12. Then, the transmitting device 10 reads the most significant digits of the freshness value stored in the storage device 12 at the time of startup. At this time, the transmitting device 10 may fail to read the most significant digits of the freshness value. FIG. 3 shows a specific example of a communication mode in the communication network system 100 when the transmitting device 10 successfully reads the most significant digits of the freshness value. Meanwhile, FIG. 4 shows a specific example of a communication mode in the communication network system 100 when the transmitting device 10 fails to read the most significant digits of the freshness value.

[0024] First, with reference to FIG. 3, a description will be given of the mode of communication in the communication network system 100 when the sending device 10 has successfully read the upper digits of the freshness value. 3, the transmission device 10 reads the most significant digits of the freshness value after starting up. The transmission device 10 starts up, for example, when the ignition switch of the vehicle is turned on.

[0025] As shown in the upper part of Fig. 3, when the sending device 10 has successfully read the upper digits, it counts up the upper digits of the freshness value. At this time, the sending device 10 counts up the upper digits that it has successfully read in the manner described with reference to Fig. 2. Meanwhile, the sending device 10 resets the lower digits of the freshness value. In this way, when the sending device 10 has successfully read the upper digits, the freshness value is set to a value consisting of the counted-up upper digits and the lower digits that have been reset to the minimum value.

[0026] As shown in the lower part of Fig. 3, the transmitting device 10 transmits a message when it receives a request to transmit a message. The transmitting device 10 transmits a message when it receives, for example, a message requesting transmission of a message from the receiving device 20. In the lower part of Fig. 3, the transmitting device 10 transmits a message including the freshness value set in the upper part of Fig. 3.

[0027] As shown in the lower part of Fig. 3, after transmitting a message, the transmitting device 10 counts up the least significant digit of the freshness value. At this time, the transmitting device 10 counts up the least significant digit of the freshness value in the manner described with reference to Fig. 2.

[0028] As shown in the lower part of Fig. 3, upon receiving a message, the receiving device 20 verifies the received message. By verifying the message, the receiving device 20 confirms the integrity of the received message. In other words, through message verification, the receiving device 20 confirms whether the message was correctly sent from the transmitting device 10, whether the message has been affected by a cyber-attack or the like, and so on.

[0029] If the receiving device 20 confirms the integrity of the received message through message verification, the message authentication is successful. On the other hand, if the receiving device 20 cannot confirm the integrity of the received message through message verification, the message authentication is unsuccessful.

[0030] The receiving device 20 verifies the message based on the freshness value included in the received message. As will be described later, if the receiving device 20 successfully authenticates the received message, it stores the freshness value included in the message in the storage device 22. The receiving device 20 verifies the message by comparing the freshness value included in the received message with the freshness value stored in the storage device 22.

[0031] For example, the receiving device 20 stores the freshness value included in the latest message among the messages that have been successfully authenticated in the storage device 22. If the freshness value included in the received message is greater than the freshness value stored in the storage device 22, the receiving device 20 succeeds in authenticating the message.

[0032] In cases where the transmitting device 10 transmits messages in rapid succession, the receiving device 20 may receive the messages in an order different from the order in which the messages were transmitted by the transmitting device 10. In anticipation of such a situation, the receiving device 20 may store in the storage device 22 the freshness values ​​contained in multiple messages that have been successfully authenticated.

[0033] For example, the receiving device 20 stores in the storage device 22 the freshness values ​​contained in the five most recent messages for which authentication has been successful. The number of freshness values ​​stored in the receiving device 20 is not limited to five. The receiving device 20 then compares the smallest freshness value stored in the storage device 22 with the freshness value contained in the received message. If the freshness value contained in the received message is greater than the smallest freshness value, the receiving device 20 checks whether the freshness value contained in the received message is the same as any of the freshness values ​​stored in the storage device 22. In other words, the receiving device 20 checks whether the freshness value contained in the received message is the same as the freshness value contained in a message that was previously successfully authenticated. If the receiving device 20 confirms that the freshness value contained in the received message is different from the freshness value contained in a message that was previously successfully authenticated, the message is successfully authenticated.

[0034] 3, if the receiving device 20 fails to authenticate a received message, it rejects the message, i.e., it discards the message without accepting it.

[0035] 3, if the receiving device 20 successfully authenticates the received message, it accepts the message and then stores the freshness value included in the accepted message in the storage device 22.

[0036] In this way, receiving device 20 accepts a message on the condition that the freshness value included in the received message is greater than the freshness value stored in the message storage unit 20. Then, receiving device 20 stores the freshness value included in the accepted message.

[0037] 3, when a message transmission request is received, the processing shown in the lower part of Fig. 3 is executed. That is, each time a message transmission request is received and the sending device 10 sends the message, it counts up the lowest digit of the freshness value. Then, upon receiving the message, the receiving device 20 verifies the message.

[0038] If receiving device 20 has stored the maximum freshness value, it will accept the next message it receives if the freshness value contained in the next message is less than the maximum value. In other words, when receiving device 20 receives a message containing the maximum freshness value, it will accept any subsequent message containing a freshness value less than the maximum value.

[0039] <Communication flow when the transmitter 10 fails to read the upper digits> Next, with reference to FIG. 4, a description will be given of a mode of communication in the communication network system 100 when the sending device 10 fails to read the upper digits of the freshness value.

[0040] In the upper part of FIG. 4, the manner in which the upper digits of the freshness value are read after the transmission device 10 is started is the same as in the upper part of FIG. As shown in the upper part of FIG. 4, if the sending device 10 fails to read the upper digits, it sets the freshness value to the maximum value.

[0041] As shown in the middle part of Fig. 4, the transmitting device 10 transmits a first message when it receives a request to transmit a message. The first message is a message that the transmitting device 10 transmits after it fails to read the most significant digits. At this time, the message transmitted by the transmitting device 10 includes the maximum freshness value set in the upper part of Fig. 4. In this way, the processing device 11 of the transmitting device 10 transmits a first message including the maximum freshness value when it fails to read the most significant digits at startup.

[0042] As shown in the middle part of Figure 4, receiving device 20 that has received the first message accepts the first message. As described above, receiving device 20 accepts a message if the freshness value included in the received message is greater than the freshness value stored by receiving device 20 itself. A maximum freshness value is likely to satisfy this condition. Note that, to ensure that receiving device 20 accepts the first message, receiving device 20 may be configured to accept a message without verifying it if it receives one containing the maximum freshness value.

[0043] As shown in the middle part of FIG. 4, upon receiving the first message, the receiving device 20 stores the freshness value included in the first message in the storage device 22. As shown in the middle part of FIG. 4, after transmitting the first message, the sending device 10 sets the freshness value to the minimum value.

[0044] As shown in the lower part of Fig. 4, after transmitting a first message, transmitting device 10 transmits a second message when receiving a message transmission request. The second message is a message transmitted by transmitting device 10 after transmitting the first message. Processing device 11 of transmitting device 10 transmits a second message including a freshness value equal to or greater than the minimum value and less than the maximum value after the first message.

[0045] The second message includes a freshness value that is equal to or greater than the minimum value and less than the maximum value. As described above, when receiving a message including the maximum freshness value, the receiving device 20 accepts a message that is received after the message and includes a freshness value that is less than the maximum value. Therefore, the receiving device 20 that has accepted the first message can successfully authenticate the second message. In this embodiment, the second message sent by the sending device 10 includes the minimum freshness value set in the middle section of FIG. 4. In other words, when sending the second message, the processing device 11 of the sending device 10 sends a message including the minimum freshness value.

[0046] 4, receiving device 20 that has received the second message accepts the second message, and then stores the freshness value included in the second message.

[0047] As shown in the lower part of Fig. 4, after transmitting the second message, the transmitting device 10 counts up the least significant digit of the freshness value. At this time, the transmitting device 10 counts up the least significant digit of the freshness value in the manner described with reference to Fig. 2.

[0048] By storing the freshness value included in the second message, receiving device 20 verifies the message received after the second message based on the freshness value included in the second message. In other words, after transmitting the second message, transmitting device 10 counts up the lowest digits of the freshness value each time it transmits a message, thereby allowing receiving device 20 to accept the transmitted message. In this way, even if transmitting device 10 fails to read the highest digits, transmitting device 10 can reset the message authentication criteria of receiving device 20 by transmitting the first message and the second message.

[0049] The transmitting device 10 includes the minimum freshness value in the second message. Therefore, the transmitting device 10 can reset the freshness value to the minimum value by the second message and restart counting up. This allows the transmitting device 10 to resume sending messages that include freshness values ​​that are successfully authenticated.

[0050] After failing to read the most significant digits of the freshness value, the transmitting device 10 periodically attempts to re-read the most significant digits. As shown in the lower part of Figure 4, if the transmitting device 10 succeeds in re-reading the most significant digits of the freshness value, it sets the freshness value to a value consisting of the most significant digit counted up by one from the read value and the least significant digit reset to the minimum value. Thereafter, the transmitting device 10 transmits messages while counting up the freshness value set after the successful read.

[0051] In this way, the processing device 11 of the transmitting device 10 re-reads the upper digits after failing to read them. Furthermore, if the processing device 11 of the transmitting device 10 succeeds in re-reading the upper digits, it counts up the read upper digits and sets a freshness value consisting of the counted-up upper digits and the minimum lower digits.

[0052] As a result, when the communication device successfully reads the upper digits by re-reading, it can resume counting up while continuing to count the upper digits up to the time when the reading of the upper digits failed. Also, the upper digits of the freshness value are information indicating the number of times the transmitting device 10 has been started. Therefore, the transmitting device 10 does not lose such information.

[0053] <Operation of this embodiment> The receiving device 20, which is the communication device on the receiving side, accepts a message if the freshness value included in the received message is greater than the freshness value stored in the receiving device 20. This condition is easily met when both the upper and lower digits of the freshness value are at their maximum values.

[0054] If the transmitting device 10, which is a communication device on the sending side, fails to read the most significant digits of the freshness value at startup, it sets the freshness value of the first message to the maximum value. This allows the transmitting device 10 to make the receiving device 20 accept the first message even if it fails to read the most significant digits of the freshness value at startup.

[0055] Furthermore, when receiving device 20 receives a message with the maximum freshness value, it stores the freshness value of the next message it receives, even if the freshness value is smaller than the maximum value. This resets the freshness value standard in receiving device 20.

[0056] The sending device 10 sets the freshness value of the second message to a value equal to or greater than the minimum value and less than the maximum value. Thereafter, the sending device 10 can send messages while counting up the freshness value, starting from the freshness value included in the second message.

[0057] <Effects of this embodiment> (1) The transmitting device 10, which is a transmitting communication device, can transmit a message including an appropriate freshness value even if it fails to read the upper digits of the freshness value.

[0058] (2) When transmitting the second message, the processing device 11 of the transmitting device 10 transmits a message including a freshness value with a minimum freshness value. The transmitting device 10 sets the minimum value as the freshness value included in the second message. In other words, the transmitting device 10 uses the value that is the furthest from the maximum value as the freshness value included in the second message. This allows the transmitting device 10 to reset the freshness value included in the message to be transmitted to the minimum value by using the second message, and restart counting up.

[0059] (3) After failing to read the most significant digits, the processing device 11 of the transmitting device 10 re-reads the most significant digits. If the processing device 11 of the transmitting device 10 succeeds in re-reading the most significant digits, the processing device 11 of the transmitting device 10 counts up the read most significant digits and sets a freshness value consisting of the counted-up most significant digits and the smallest value of the least significant digits.

[0060] If the re-reading of the upper digits is successful, the transmitting device 10 sets the freshness value using the value that was successfully read. As a result, if the re-reading of the upper digits is successful, the transmitting device 10 can resume counting up while continuing the count of the upper digits up to the time before the reading of the upper digits failed.

[0061] (4) The communication network system 100 is composed of multiple communication devices. In message exchange between the communication devices, the transmitting device 10, which is the communication device on the sending side that sends the message, transmits a message containing a freshness value within a predetermined range composed of upper and lower digits. The upper digits are counted up each time the transmitting device 10 starts up. The lower digits are counted up each time the transmitting device 10 sends a message. In message exchange between the communication devices, the receiving device 20, which is the communication device on the receiving side that receives the message, accepts the message on the condition that the freshness value included in the received message is greater than the freshness value stored in the receiving device 20. The receiving device 20 also stores the freshness value included in the accepted message. When the receiving device 20 receives a message containing the maximum freshness value, it also accepts any message received after the message containing a freshness value less than the maximum value. In the communication network system 100, when the transmitting device 10 fails to read the upper digits at startup, it transmits a first message containing the maximum freshness value. Then, after the first message, the transmitting device 10 transmits a second message including a freshness value that is equal to or greater than the minimum value and less than the maximum value.

[0062] In communication network system 100, if transmitting device 10 fails to read the most significant digits of the freshness value at startup, it sets the freshness value of the first message to the maximum value. Thereafter, in communication network system 100, transmitting device 10 sets the freshness value of the second message to a value equal to or greater than the minimum value and less than the maximum value. Thereafter, transmitting device 10 can send messages while counting up the freshness value, starting from the freshness value included in the second message. In this way, communication network system 100 can send messages containing an appropriate freshness value, even if the sending communication device fails to read the most significant digits of the freshness value.

[0063] (5) The communication method is applied to a transmitting device 10, which is a transmitting-side communication device that transmits a message in message exchange between communication devices in a communication network system 100. The communication network system 100 is composed of multiple communication devices. In message exchange between the communication devices, the transmitting device 10 transmits a message including a freshness value within a predetermined range, which is composed of upper digits that are counted up each time the device is started and lower digits that are counted up each time a message is sent. In message exchange between the communication devices, a receiving device 20, which is a receiving-side communication device that receives the message in the message exchange, accepts the message on the condition that the freshness value included in the received message is greater than a freshness value stored in the receiving device 20. The receiving device 20 also stores the freshness value included in the accepted message. Then, when the receiving device 20 receives a message including a maximum freshness value, the receiving device 20 accepts a message received after the message including a freshness value less than the maximum value. The communication method includes a step in which the transmitting device 10 transmits a first message including the maximum freshness value when reading the upper digits at startup fails. The communication method includes a step in which the transmitting device 10 transmits, after the first message, a second message including a freshness value greater than or equal to the minimum value and less than the maximum value.

[0064] In the communication method, if the sending device 10 fails to read the most significant digits of the freshness value at startup, the sending device 10 sets the freshness value of the first message to the maximum value. Thereafter, the communication method causes the sending device 10 to set the freshness value of the second message to a value equal to or greater than the minimum value and less than the maximum value. Thereafter, the sending device 10 can send messages while counting up the freshness value, starting from the freshness value included in the second message. In this way, the communication method can send a message including an appropriate freshness value even if the sending communication device fails to read the most significant digits of the freshness value.

[0065] <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0066] In the above embodiment, two communication devices, a transmitting device 10 and a receiving device 20, are connected to the communication network system 100. The manner in which the communication devices are connected in the communication network system 100 is not limited to the above embodiment. In other words, the topology of the communication devices in the communication network system 100 is not limited to the above embodiment. Furthermore, the number of communication buses in the communication network system 100 and the number of connected communication devices are not limited to the above embodiment.

[0067] In the above embodiment, the communication devices in the communication network system 100 are connected via the communication bus 30. However, the communication devices in the communication network system 100 may be connected wirelessly.

[0068] In the above embodiment, the transmitting device 10 transmits a message including a minimum freshness value as the second message. On the other hand, the freshness value included in the second message transmitted by the transmitting device 10 may be greater than the minimum value and less than the maximum value. [Explanation of symbols]

[0069] 10...transmitting device, 11...processing device, 12...storage device, 20...receiving device, 21...processing device, 22...storage device, 30...communication bus, 100...communication network system

Claims

1. It is composed of a plurality of communication devices, In message exchange between the communication devices, a sending communication device that sends the message, Sending the message including a freshness value within a predetermined range, the freshness value being configured by a high-order digit that is counted up each time the device is started and a low-order digit that is counted up each time the message is sent; A receiving communication device that receives the message, Accepting the message on the condition that the freshness value included in the received message is greater than the freshness value stored in the message storage; storing the freshness value included in the received message; In a communication network system, when receiving a message including the freshness value of a maximum value, the system accepts a message received after the message including the freshness value that is less than the maximum value, the transmitting communication device, a processing device; When the reading of the upper digits fails at startup, The processing device sending a first message including the maximum freshness value; sending, after the first message, a second message including the freshness value greater than or equal to a minimum value and less than a maximum value. Communication equipment.

2. The processing device includes: When transmitting the second message, transmitting the message containing the freshness value with the minimum value. The communication device according to claim 1 .

3. The processing device includes: After failing to read the most significant digits, re-reading the most significant digits; If the re-reading of the upper digits is successful, counting up the read upper digits and setting the freshness value consisting of the counted-up upper digits and the minimum value of the lower digits.

3. The communication device according to claim 1.

4. It is composed of a plurality of communication devices, In message exchange between the communication devices, a sending communication device that sends the message, Sending the message including a freshness value within a predetermined range, the freshness value being configured by a high-order digit that is counted up each time the device is started and a low-order digit that is counted up each time the message is sent; A receiving communication device that receives the message, Accepting the message on the condition that the freshness value included in the received message is greater than the freshness value stored in the message storage; storing the freshness value included in the received message; a communication network system that, when receiving a message including the freshness value of a maximum value, accepts a message received after the message including the freshness value that is less than the maximum value; The transmitting communication device When reading of the upper digits fails at startup, a first message including the freshness value of the maximum value is transmitted; After the first message, send a second message containing the freshness value greater than or equal to the minimum value and less than the maximum value. Communication network system.

5. It is composed of a plurality of communication devices, In message exchange between the communication devices, a sending communication device that sends the message, Sending the message including a freshness value within a predetermined range, the freshness value being configured by a high-order digit that is counted up each time the device is started and a low-order digit that is counted up each time the message is sent; A receiving communication device that receives the message, Accepting the message on the condition that the freshness value included in the received message is greater than the freshness value stored in the message storage; storing the freshness value included in the received message; In a communication network system, when receiving a message including the freshness value of a maximum value, the system accepts a message received after the message including the freshness value that is less than the maximum value, a communication method applied to the transmitting communication device, When the transmitting communication device fails to read the upper digits at startup, sending a first message including the maximum freshness value; sending, after the first message, a second message including the freshness value greater than or equal to a minimum value and less than a maximum value; Contains Communication method.

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