Control system, relay device, and communication method

A relay device connected to a first controller via a first transmission path and connected to a second controller via a second transmission path, the relay device comprising:

• a first interface for connection to the first transmission path;
• a second interface for connection to the second transmission path;
• a detection unit configured to detect a communication state of the first transmission path;
• and
• a processing circuit configured to, in accordance with a transfer setting,
• transmit, to the second controller output data transmitted from the first controller, and transmit, to the second controller, first state data indicating the detected communication state of the first transmission path,
• wherein the first state data includes time data indicating a time of detection of the communication state.

A communication method performed by a control system including a first controller including an interface for connection to a first transmission path and a second controller including an interface for connection to a second transmission path, the communication method comprising:

• detecting a communication state of the first transmission path;
• transmitting, to the second controller in accordance with a transfer setting, output data transmitted from the first controller;
• and
• transmitting, to the second controller, first state data indicating the communication state of the first transmission path,
• wherein the first state data includes time data indicating a time of detection of the communication state.