Relay system, communication device, and delay period determination method

A communication circuitry configured to

• receive, from a first circuitry, an original signal including a plurality of control codes communicated in time order,
• transmit, to an opposing circuitry connected through an optical fiber, an optical signal including the original signal and information added to the original signal, the information being directed to the opposing circuitry,
• receive, from the opposing circuitry, an optical signal including the original signal and information added to the original signal, the information being from the opposing circuitry, and
• transmit, to the first circuitry, the original signal based on the received optical signal,
• the communication circuitry comprising:
• a first optical transceiver connected to the optical fiber;
• an estimating circuit configured to acquire, based on a dispersion compensation amount acquired by the first optical transceiver or a second optical transceiver included in the opposing circuitry and connected to the optical fiber, an estimated value of a transmission delay period, the transmission delay period being a period during which the optical signal is transmitted through the optical fiber;
• a specifying circuit configured to specify, based on the estimated value of the transmission delay period acquired by the estimating circuit, a reception-related time when a transmission-related time is known, or the transmission-related time when the reception-related time is known, the transmission-related time being related to transmission of a control code by the communication circuitry or the opposing circuitry, the reception-related time being related to reception of the control code by the opposing circuitry or the communication circuitry;
• and
• a determining circuit configured to determine, based on the transmission-related time and the reception-related time, the transmission delay period in a first transmission direction from the communication circuitry toward the opposing circuitry or a second transmission direction from the opposing circuitry toward the communication circuitry.

A delay period determination method for determining, by a communication circuitry, a delay period in a relay system in which the communication circuitry and an opposing circuitry are connected to each other through an optical fiber, the delay period determination method comprising:

• acquiring, based on a dispersion compensation amount acquired by a first optical transceiver included in the communication circuitry and connected to the optical fiber or a second optical transceiver included in the opposing circuitry and connected to the optical fiber, an estimated value of a transmission delay period, the transmission delay period being a period during which an optical signal is transmitted through the optical fiber;
• specifying, based on the estimated value of the transmission delay period acquired by an estimating circuit, a reception-related time when a transmission-related time is known, or the transmission-related time when the reception-related time is known, the transmission-related time being related to transmission of a control code by the communication circuitry or the opposing circuitry, the reception-related time being related to reception of the control code by the opposing circuitry or the communication circuitry;
• and
• determining, based on the transmission-related time and the reception-related time, the transmission delay period in a first transmission direction from the communication circuitry toward the opposing circuitry or a second transmission direction from the opposing circuitry toward the communication circuitry.