Communication system, communication method, and electronic control device

Abstract

This electronic control device, with another electronic control device, executes communication start processing necessary for starting periodic communication processing for each first predetermined time, and when the communication start processing is successful, executes the periodic communication processing for a second predetermined time. The periodic communication processing is processing for periodically executing communication of a predetermined message with the other electronic control device, and the second predetermined time is longer than twice the length of the first predetermined time.

Description

Communication system, communication method, and electronic control device

[0001] The present invention relates to a communication system, a communication method, and an electronic control device.

[0002] A technology is known in which, in an in-vehicle network, a server requests and approves the provision of a service to a client, and the server provides periodic messages to the client as part of the service provision (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2022-109205

[0004] However, the technology described in Patent Document 1 has the problem that if the server attempts to request and approve the delivery of a message again and fails while the server is delivering the periodic message, the delivery of the periodic message will be interrupted.

[0005] The problem to be solved by the present invention is to provide a communication system, a communication method, and an electronic control device that can continue to provide periodic messages.

[0006] The present invention solves the above problem by executing a communication start process necessary to start periodic communication processing every first predetermined time, and if the communication start process is successful, executing the periodic communication process for a second predetermined time, the periodic communication process being a process for periodically executing communication of a predetermined message, and the second predetermined time being longer than twice the length of the first predetermined time.

[0007] According to the present invention, periodic message provision can be continued.

[0008] Fig. 1 is a block diagram showing the configuration of a communication system according to this embodiment. Fig. 2 is a sequence chart illustrating an example of message transmission and reception between electronic control devices in the prior art. Fig. 3 is a sequence chart illustrating an example of message transmission and reception between electronic control devices in this embodiment. Fig. 4 is a sequence chart illustrating an example of determining whether communication between electronic control devices has been interrupted in the prior art. Fig. 5 is a sequence chart illustrating an example of determining whether communication between electronic control devices has been interrupted in this embodiment.

[0009] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a communication system, a communication method, and an electronic control device according to the present invention will be described using an example in which they are applied to an in-vehicle communication system installed in an automobile (also referred to as a vehicle). In the in-vehicle communication system according to this embodiment, multiple electronic control devices are connected to a communication network using SOME / IP (Service Oriented Middleware on Internet Protocol), a standard for Ethernet (registered trademark) control communication for automobiles. The electronic control devices will also be referred to as ECUs (Electronic Control Units). Each ECU is connected to other ECUs so as to be able to communicate with each other and can send and receive messages. The ECUs are connected to in-vehicle devices such as sensors and actuators and control various in-vehicle devices. The ECUs include, for example, a body-related ECU, a driving-related ECU, a power supply-related ECU, a driving assistance-related ECU, a multimedia-related ECU, and a sensor-related ECU.

[0010] Although not shown in detail, each ECU includes a controller and a communication circuit. The controller includes a CPU, a ROM in which a control program executed by the CPU is stored, and a RAM used as a work area for the control program. The controller functions as an ECU by executing the control program with the CPU. The communication circuit is controlled by the controller and performs communication between the controller and the communication network 13.

[0011] FIG. 1 is a block diagram showing the configuration of a communication system according to this embodiment. The communication system 10 includes a server ECU 11 and a client ECU 12. The server ECU 11 is an ECU that provides services to other ECUs. In this embodiment, the server ECU 11 transmits periodic messages in a periodic communication process described below to provide the services. The client ECU 12 is an ECU that receives services from other ECUs. In this embodiment, the client ECU 12 receives periodic messages in a periodic communication process described below. The server ECU 11 and the client ECU 12 are connected by wire and transmit and receive messages via a communication network 13. In the communication network 13, messages are transmitted and received between the ECUs via Ethernet communication in accordance with the SOME / IP communication protocol.

[0012] The server ECU 11 and the client ECU 12 are examples of "one electronic control device" and "the other electronic control device" as set forth in the claims. The server ECU 11 may be "one electronic control device" or "the other electronic control device." The client ECU 12 may be "one electronic control device" or "the other electronic control device." Note that the communication system 10 is not limited to having a single server ECU 11 and a single client ECU 12, and may include a plurality of server ECUs 11 and a plurality of client ECUs 12, each connected via a communication network. Furthermore, one server ECU 11 may be connected to a plurality of client ECUs 12, and one client ECU 12 may be connected to a plurality of server ECUs 11.

[0013] In the following example, the server ECU 11 will be described as an ECU that controls a forward-facing camera mounted on the front of the vehicle, and the client ECU 12 will be described as an ECU that comprehensively controls various functions in an Advanced Driver-Assistance System (ADAS). The client ECU 12 that controls the driving assistance system may be connected to not only an ECU that controls the forward-facing camera, but also an ECU that provides necessary sensor information. The ECU that provides necessary sensor information may be, for example, an ECU that controls a radar mounted on the vehicle. The server ECU 11 and the client ECU 12 are not limited to ECUs for sensors or driving systems such as ADAS, but may also be multimedia ECUs that provide entertainment to the occupants. For example, the server ECU 11 may be a playback device that plays back videos recorded on a DVD, and the client ECU 12 may be a display device that displays the videos.

[0014] The server ECU 11 transmits a message including sensor information as a service. The message including sensor information is an example of a predetermined message. Specifically, the server ECU 11 acquires sensor information indicating the detection results of the front camera from the connected front camera, and generates a message including the acquired sensor information. The message generated by the server ECU 11 is transmitted to the client ECU 12 via the communication network 13.

[0015] The client ECU 12 receives a message including the sensor information transmitted from the server ECU 11 via the communication network 13. The client ECU 12 controls in-vehicle devices such as actuators based on the detection results included in the received message, thereby providing driving assistance for the vehicle.

[0016] In this embodiment, the server ECU 11 and the client ECU 12 execute a communication start process and a periodic communication process between the server ECU 11 and the client ECU 12. The communication start process is a process necessary to start the periodic communication process. The communication start process includes a so-called SD (Service Discovery). The communication start process is executed at first predetermined time intervals. For example, the communication start process includes a service proposal process that transmits an Offer message indicating that a service is provided, a service request process that transmits a Subscribe message indicating a request for the provision of the service, and a service approval process that transmits a Sub_Ack message indicating approval of the provision of the service. In this embodiment, in the communication start process, the server ECU 11 executes the service proposal process and the service approval process. Furthermore, the client ECU 12 executes the service proposal process. Specific processing procedures will be described later.

[0017] The periodic communication process is a process for periodically communicating a predetermined message. The predetermined message is a message transmitted from the server ECU 11 to the client ECU 12 via SOME / IP. For example, the predetermined message is a message storing information related to the provision of a service. Specifically, the information related to the provision of a service is information acquired from an in-vehicle device controlled by the server ECU 11. Hereinafter, the predetermined message periodically communicated in the periodic communication process is also referred to as a periodic message. If the server ECU 11 is an ECU that controls a camera, the predetermined message is a message storing sensor information. In the periodic communication process, the server ECU 11 periodically transmits a predetermined message to the client ECU 12, and the client ECU 12 receives the predetermined message transmitted from the server ECU 11. The periodic communication process is executed during a second predetermined time.

[0018] The second predetermined time is longer than twice the length of the first predetermined time. For example, the second predetermined time is set to a time longer than twice the length of the first predetermined time but shorter than three times the length of the first predetermined time. In other words, the communication initiation process is executed twice within one cycle of executing the periodic communication process. The second predetermined time may also be longer than three times the length of the first predetermined time. For example, the second predetermined time is set to a time longer than three times the length of the first predetermined time but shorter than four times the length of the second predetermined time. In this case, the communication initiation process is executed three times within one cycle of executing the periodic communication process. As described above, even if the first communication initiation process is successful and then fails, the possibility of the periodic communication process being interrupted can be reduced by executing the communication initiation process a second and third time before the second predetermined time of the periodic communication process has elapsed.

[0019] Here, the procedures of the communication start process and the periodic communication process will be described. First, the server ECU 11 and the client ECU 12 execute the communication start process. In the communication start process, the server ECU 11 executes a service proposal process in which an Offer message is sent to the client ECU 12 every time a first predetermined time period elapses. When the client ECU 12 receives the Offer message from the server ECU 11, the server ECU 11 executes a service request process in which a Subscribe message is sent to the server ECU 11. When the server ECU 11 receives the Subscribe message from the client ECU 12, the server ECU 11 executes a service approval process in which a Sub_Ack message is sent to the client ECU 12.

[0020] If the service proposal process, service request process, and service approval process are all executed normally, the communication initiation process is determined to be successful. If any of the processes is not executed normally, the communication initiation process is determined to have failed. The determination of whether the communication initiation process is successful is performed by the server ECU 11 and / or the client ECU 12. For example, if one ECU does not receive a message that should have been sent in the communication initiation process from the other ECU, the communication initiation process is determined to have failed. In this embodiment, the success of the communication initiation process is also referred to as the establishment of a contract. When the contract is established, the contract period (Time To Live, TTL) begins. In other words, the contract period is a second predetermined time.

[0021] The server ECU 11 executes the periodic communication process if the communication start process is successful. Specifically, when the server ECU 11 receives a Subscribe message and transmits a Sub_Ack message, the server ECU 11 determines that the communication start process is successful and starts the periodic communication process. In the periodic communication process, the server ECU 11 periodically transmits a predetermined message to the client ECU 12 for a second predetermined time period after determining that the communication start process is successful. The client ECU 12 receives the predetermined message each time the server ECU 11 transmits the predetermined message. The client ECU 12 continuously provides driving assistance based on the sensor information stored in the periodically transmitted predetermined message. When the second predetermined time period has elapsed, the server ECU 11 terminates the periodic transmission of the predetermined message. At this time, if the next communication start process is successful within the second predetermined time period, the server ECU 11 continues the periodic communication process without terminating the periodic communication process.

[0022] Here, a communication method according to this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a sequence chart for explaining an example of message transmission and reception between electronic control units in the prior art. First, an example of message transmission and reception in the prior art will be described.

[0023] As shown in FIG. 2 , in step S11, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S12, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. The server ECU 11 receives the Subscribe message from the client ECU 12. In step S13, the server ECU 11 transmits a Sub_Ack message to the client ECU 12. When the processes of steps S11 to S13 have been executed, the server ECU 11 determines that the communication start process has been successful, and proceeds to step S14. In step S14, the server ECU 11 starts the periodic communication process. Specifically, the server ECU 11 periodically transmits a periodic message for a second predetermined time period ("time period A" in FIG. 2 ).

[0024] When a first predetermined time ("time C" in FIG. 2) has elapsed since the processing of step S11, the server ECU 11 executes a communication start process. In step S15, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S16, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In this embodiment, it is assumed that the client ECU 12 fails to transmit the Subscribe message, and the server ECU 11 cannot receive the Subscribe message. In this case, the server ECU 11 ends the periodic transmission of the periodic message when a second predetermined time ("time A" in FIG. 2) has elapsed. When a first predetermined time period ("time C" in FIG. 2) has elapsed since the execution of the communication start process in step S15, the server ECU 11 starts the communication start process and transmits an Offer message in step S17. Therefore, transmission of periodic messages is stopped during the time period from the end of the periodic transmission of periodic messages to the start of transmission of Offer messages ("time B" in FIG. 2).

[0025] Next, an example of message transmission and reception between electronic control units in this embodiment will be described. FIG. 3 is a sequence chart for describing an example of message transmission and reception between electronic control units in this embodiment. As shown in FIG. 3, in step S21, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S22, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. The server ECU 11 receives the Subscribe message transmitted from the client ECU 12. In step S23, the server ECU 11 transmits a Sub_Ack message to the client ECU 12. The client ECU 12 receives the Sub_Ack message from the server ECU 11. When the processes of steps S21 to S23 have been executed, the server ECU 11 determines that the communication start process has been successful, and proceeds to step S24. In step S24, the server ECU 11 starts a periodic communication process. Specifically, the server ECU 11 periodically transmits a periodic message for a second predetermined time period ("time period A" in FIG. 3).

[0026] When a first predetermined time ("time C" in FIG. 3) has elapsed since the processing of step S21, the server ECU 11 executes a communication start process. In step S25, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S26, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In this embodiment, it is assumed that the client ECU 12 fails to transmit the Subscribe message and the server ECU 11 cannot receive the Subscribe message. Furthermore, when a first predetermined time ("time C" in FIG. 3) has elapsed since the processing of step S25, the server ECU 11 proceeds to step S27. In step S27, the server ECU 11 transmits an Offer message. The client ECU 12 receives the Offer message from the server ECU 11. In step S28, if the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In step S29, the server ECU 11 transmits a Sub_Ack message to the client ECU 12. If the processes of steps S27 to S29 have been executed, the server ECU 11 determines that the communication start process has been successful and proceeds to step S30. In step S30, the server ECU 11 starts the periodic communication process. Specifically, the server ECU 11 periodically transmits periodic messages for a second predetermined time. As a result, even if step S26 fails, the communication start process can be executed again before the second predetermined time has elapsed, preventing the periodic communication process from being interrupted.

[0027] The second predetermined time period may be set to a different value depending on the importance of the message. For example, if the message has a high importance, the second predetermined time period is set to be shorter than if the message has a low importance.

[0028] The importance of a predetermined message may also be determined based on the type of the predetermined message. In this embodiment, the types of predetermined messages include messages related to vehicle driving and messages related to the provision of entertainment. That is, a predetermined message used for vehicle driving is considered to be more important than a predetermined message used for the provision of entertainment. The predetermined messages used for vehicle driving include messages transmitted from the body system ECU, driving system ECU, power supply system ECU, driving assistance system ECU, and sensor system ECU. The predetermined messages used for the provision of entertainment include messages transmitted from the multimedia system ECU. If the predetermined message is related to vehicle driving, the second predetermined time is set to be shorter than the second predetermined time if the predetermined message is related to the provision of entertainment. For example, if the predetermined message is related to vehicle driving, the second predetermined time is set to be more than twice the length of the first predetermined time. If the predetermined message is related to the provision of entertainment, the second predetermined time is set to be more than three times the length of the first predetermined time. The importance of a predetermined message may also be determined based on whether the message is transmitted from an ECU related to vehicle safety. For example, the importance of a predetermined message is set according to a predetermined level (a level that defines a functional safety standard) such as ASIL.

[0029] The second predetermined time may be set to a different value depending on the surrounding environment of the harness for transmitting and receiving the predetermined message. The harness connects the server ECU 11 and the client ECU 12. If the surrounding environment of the harness is prone to communication interference, the second predetermined time may be set to a shorter value than the second predetermined time if the surrounding environment of the harness is not prone to communication interference. For example, if there is another harness, such as a motor, that is in heavy communication and through which a large current flows around the harness, the harness is prone to communication interference.

[0030] In the present embodiment, the server ECU 11 and the client ECU 12 also perform a disruption determination. The disruption determination is a determination of whether communication has been disrupted. The server ECU 11 and the client ECU 12 determine that communication has been disrupted when the communication start process has failed two or more times in a row. For example, the server ECU 11 and the client ECU 12 may determine that communication has been disrupted when the communication start process has failed two or more times in a row, or may determine that communication has been disrupted when the communication start process has failed three or more times in a row. If the predetermined message is a message related to vehicle driving, the server ECU 11 and the client ECU 12 determine that communication has been disrupted when the communication start process has failed two or more times in a row. If the predetermined message is a message related to the provision of entertainment, the server ECU 11 and the client ECU 12 determine that communication has been disrupted when the communication start process has failed three or more times in a row. The disruption determination may be performed by both the server ECU 11 and the client ECU 12, or by either one of them.

[0031] By performing the above-described communication disruption determination, a communication disruption can be detected more quickly. For example, if the first predetermined time is set to 0.25 seconds, the server ECU 11 and the client ECU 12 determine that communication has been disrupted after two failed attempts, and can therefore determine that communication has been disrupted in 0.5 seconds. On the other hand, in conventional technologies such as CAN communication, a communication disruption is determined when no communication has been received for two seconds after transmission has stopped, which takes time to determine that communication has been disrupted. In this embodiment, when a communication disruption determination is made, the server ECU 11 and the client ECU 12 may notify the vehicle user and an external server of communication disruption information, or may switch control methods to control in-vehicle devices using information obtained from a network other than the communication network where communication has been disrupted.

[0032] Here, the communication method according to this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a sequence chart for explaining an example of determining whether communication between electronic control units has been interrupted in the prior art. First, the determination of communication interruption in the prior art will be described.

[0033] As shown in FIG. 4 , in step S31, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S32, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In step S33, the server ECU 11 transmits a Sub_Ack message to the client ECU 12. When the processes of steps S31 to S33 have been executed, the server ECU 11 determines that the communication start process has been successful, and proceeds to step S34. In step S34, the server ECU 11 starts periodic communication processing. Specifically, the server ECU 11 periodically transmits periodic messages for a second predetermined time period ("time period A" in FIG. 4 ).

[0034] When a first predetermined time period ("time C" in FIG. 4 ) has elapsed since the processing of step S31, the server ECU 11 executes a communication start process. In step S35, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S36, when the client ECU 12 receives the Offer message, the client ECU 12 transmits a Subscribe message to the server ECU 11. In this embodiment, it is assumed that the client ECU 12 fails to transmit the Subscribe message, and the server ECU 11 cannot receive the Subscribe message. In this case, when time D has elapsed since the end of transmission of the periodic message, the client ECU 12 determines that communication with the server ECU 11 has been interrupted. Therefore, transmission of the periodic message is stopped for the time from the end of periodic transmission of the periodic message to the time when the interruption determination is made ("time D" in FIG. 4 ).

[0035] Next, an example of determining whether communication between electronic control units has been interrupted in this embodiment will be described below. Fig. 5 is a sequence chart for explaining an example of determining whether communication between electronic control units has been interrupted in this embodiment.

[0036] As shown in FIG. 5 , in step S41, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S42, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In step S43, the server ECU 11 transmits a Sub_Ack message to the client ECU 12. When the processes of steps S41 to S43 have been executed, the server ECU 11 determines that the communication start process has been successful, and proceeds to step S44. In step S44, the server ECU 11 starts periodic communication processing. Specifically, the server ECU 11 periodically transmits periodic messages for a second predetermined time period ("time period A" in FIG. 5 ).

[0037] When a first predetermined time ("time C" in FIG. 5) has elapsed since the processing of step S41, the server ECU 11 executes a communication start process. In step S45, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S46, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In this embodiment, it is assumed that the client ECU 12 fails to transmit the Subscribe message and the server ECU 11 cannot receive the Subscribe message. In this case, the server ECU 11 determines that the communication start process has failed once.

[0038] When a first predetermined time (time C) has elapsed since the processing of step S45, the server ECU 11 executes a communication start process. In step S47, the server ECU 11 transmits an Offer message to the client ECU 12. The client ECU 12 receives the Offer message from the server ECU 11. In step S48, when the client ECU 12 receives the Offer message, it transmits a Subscribe message to the server ECU 11. In this embodiment, it is assumed that the client ECU 12 fails to transmit the Subscribe message and the server ECU 11 cannot receive the Subscribe message. In this case, the server ECU 11 determines that the communication start process has failed two consecutive times, and proceeds to step S49. In step S49, the server ECU 11 determines that communication with the client ECU 12 has been interrupted.

[0039] As described above, in the communication system and communication method according to this embodiment, one electronic control unit executes a communication initiation process required to start periodic communication processing with another electronic control unit at every first predetermined time, and if the communication initiation process is successful, executes the periodic communication process for a second predetermined time, where the periodic communication process is a process for periodically executing communication of a predetermined message with the other electronic control unit, and the second predetermined time is longer than twice the length of the first predetermined time. This allows the periodic message delivery to continue.

[0040] In the communication system and method according to this embodiment, one electronic control device and / or the other electronic control device calculates the number of times the communication initiation process has failed, and if the communication initiation process has failed two or more times in a row, determines that communication between the one electronic control device and the other electronic control device has been interrupted. This allows for earlier determination of communication interruption.

[0041] In the communication system and communication method according to the present embodiment, the second predetermined time is set to be shorter when the importance of the message is high than when the importance of the message is low, thereby making it possible to change the time for which the periodic communication process is executed depending on the importance of the message.

[0042] In the communication system and communication method according to the present embodiment, the predetermined message includes a message related to vehicle driving and a message related to the provision of entertainment, and the second predetermined time is set to be shorter when the predetermined message is a message related to vehicle driving than when the predetermined message is a message related to the provision of entertainment. This makes it possible to change the time for which the periodic communication process is executed depending on whether the message is related to vehicle driving or the provision of entertainment.

[0043] Furthermore, in the communication system and communication method according to this embodiment, when the surrounding environment of the harness connecting one electronic control device and the other electronic control device is susceptible to communication interference, the second predetermined time is set to be shorter than the second predetermined time when the surrounding environment is not susceptible to communication interference. This makes it possible to change the time for executing the periodic communication process depending on whether the surrounding environment of the harness connecting one electronic control device and the other electronic control device is susceptible to communication interference.

[0044] In this embodiment, an electronic control device that is communicatively connected to another electronic control device executes a communication initiation process required to initiate periodic communication with the other electronic control device at every first predetermined time, and if the communication initiation process is successful, executes the periodic communication process for a second predetermined time, where the periodic communication process is a process for periodically communicating a predetermined message with the other electronic control device, and the second predetermined time is longer than twice the length of the first predetermined time, thereby enabling the periodic message provision to continue.

[0045] It should be noted that the above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above-described embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0046] 10: Communication system 11: Server ECU 12: Client ECU 13: Communication network

Claims

1. A communication system comprising a plurality of electronic control devices connected to each other so that they can communicate with each other, wherein one electronic control device executes a communication initiation process necessary to initiate periodic communication processing with the other electronic control device at every first predetermined time, and if the communication initiation process is successful, executes the periodic communication process for a second predetermined time, wherein the periodic communication process is a process for periodically communicating a predetermined message with the other electronic control device, and the second predetermined time is longer than twice the length of the first predetermined time.

2. A communication system as claimed in claim 1, wherein the one electronic control device and / or the other electronic control device calculates the number of times the communication start process has failed, and if the communication start process has failed two or more times in succession, determines that communication between the one electronic control device and the other electronic control device has been interrupted.

3. A communication system according to claim 1 or 2, wherein the second predetermined time is set shorter when the importance of the specified message is high than when the importance of the specified message is low.

4. A communication system according to any one of claims 1 to 3, wherein the predetermined messages include messages related to the running of the vehicle and messages related to the provision of entertainment, and the second predetermined time is set shorter when the predetermined message is a message related to the running of the vehicle than when the predetermined message is a message related to the provision of entertainment.

5. A communication system as claimed in any one of claims 1 to 4, wherein the second predetermined time is set to be shorter when the surrounding environment of the harness for connecting the one electronic control device and the other electronic control device is susceptible to communication interference than the second predetermined time when the surrounding environment is not susceptible to communication interference.

6. A communication method executed by a plurality of electronic control devices connected to each other so that they can communicate with each other, wherein one electronic control device executes a communication initiation process necessary to start periodic communication processing with the other electronic control device at every first predetermined time, and if the communication initiation process is successful, executes the periodic communication process for a second predetermined time, wherein the periodic communication process is a process for periodically communicating a predetermined message with the other electronic control device, and the second predetermined time is longer than twice the length of the first predetermined time.

7. An electronic control device that is communicatively connected to another electronic control device, which executes a communication start process necessary to start periodic communication processing with the other electronic control device at every first predetermined time, and if the communication start process is successful, executes the periodic communication process for a second predetermined time, wherein the periodic communication process is a process for periodically communicating a predetermined message with the other electronic control device, and the second predetermined time is longer than twice the length of the first predetermined time.

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