Relay device, communication network system, and communication control method

A communication network system comprising:

• a first electric control unit connected to a first communication network;
• a second electric control unit connected to a second communication network, the second communication network using a communication protocol different from a communication protocol of the first communication network;
• and
• a relay device connected to the first communication network and the second communication network, the relay device being configured to receive a second frame storing at least one first frame,
• wherein the first frame is transmitted in the first communication network, and has a first payload including control information, a CAN ID for identifying the control information, and a data length code (DLC CAN) indicating a data length of the first payload,
• wherein the CAN FD frame is transmitted in the second communication network, and has an ID field and a data field, the ID field including a CAN FD ID that indicates the CAN frame is included and a data length code (DLC FD) indicating a data length of the data field,
• wherein the data field includes a plurality of the CAN frames and MAC,
• wherein the MAC is stored in a storage area that is located at positions behind the plurality of CAN frames in the data field,
• wherein the relay device is further configured to
• perform frame recognition process for recognizing the plurality of the CAN frames,
• wherein the frame recognition process includes
• recognizing that the CAN frame is stored by identifying the CAN FD ID in the ID field,
• reading data of the CAN frame to identify the CAN ID and the DLC CAN
• identifying a frame delimiter of the plurality of the CAN frames from the DCL CAN, and
• identifying the storage area including a counter value and the MAC by identifying the end of the data field from the DLC FD,
• end the frame recognition process after identifying the last stored CAN frame out of the plurality of CAN frames,
• acquire the MAC in the storage area,
• compare the acquired MAC with a MAC for verification, and
• determine that a received data frame is valid data if the acquired MAC and the MAC for verification match.

A communication control method to be executed by a relay device connected between a first communication network and a second communication network, the second communication network using a communication protocol different from a communication protocol of the first communication network, the method comprising:

• receiving a CAN FD from the second communication network, the CAN FD having an ID field and a data field, the ID field including a CAN FD ID that indicates the CAN frame is included and a data length code (DLC FD) indicating a data length of the data field, the data field including a plurality of the CAN frames and MAC, the MAC stored in a storage area that is located at positions behind the plurality of CAN frames in the data field;
• performing frame recognition process for recognizing the plurality of CAN frames, the CAN frames transmitted in the first communication network, and each of the CAN frames having a first payload including control information, a CAN ID for identifying the control information, and a data length code (DLC CAN) indicating a data length of the first payload,
• wherein the frame recognition process includes
• recognizing that the CAN frame is stored by identifying the CAN FD ID in the ID field,
• reading data of the CAN frame to identify the CAN ID and the DLC CAN,
• identifying a frame delimiter of the plurality of the CAN frames from the DCL CAN, and
• identifying the storage area including a counter value and the MAC by identifying the end of the data field from the DLC FD;
• ending the frame recognition process after identifying the last stored CAN frame out of the plurality of CAN frames;
• acquiring the MAC in the storage area;
• comparing the acquired MAC with a MAC for verification;
• determining that a received data frame is valid data if the acquired MAC and the MAC for verification match;
• and
• transmitting the recognized first frame to the first communication network.