Communication system, relay device, reception device, and communication control method

A receiving device connected to a communication network for receiving data frames transmitted from a transmission device connected to the communication network, the receiving device comprising:

• an electronic controller configured to
• receive the data frames in which counter values indicating a number of transmissions of the data frames to the communication network are stored,
• store counter value management information for managing the counter values of the data frames transmitted by the transmission device,
• receive the data frames in which the counter values are stored, and
• verify validity of received data frames based on the counter value of the received data frames and the counter value management information,
• the counter value of a prescribed numerical width being registered in the counter value management information, and
• the numerical width of the counter value registered in the counter value management information being controlled.

A communication control method executed by a relay device that relays communication between a first electronic controller and a second electronic controller connected to a communication network, wherein

• the first electronic controller
• includes a counter for counting a number of transmissions of data frames to the communication network, and
• is configured to transmit the data frames in which counter values of the counter are stored to the communication network,
• the second electronic controller is configured to
• store counter value management information for managing the counter values of the data frames transmitted by the first electronic controller,
• receive the data frames in which the counter values are stored, and
• verify validity of received data frames based on whether the counter value of the received data frames is registered in the counter value management information,
• the counter value of a prescribed numerical width being registered in the counter value management information, and
• the second electronic controller being configured to control the numerical width of the counter value registered in the counter value management information.