Transmission device, time transmission system, and delay compensation method

A time transmission system comprising a transmission device, the time transmission system configured to synchronize time of a second time synchronization device based on time information of transmission and reception of packets for time synchronization between a first time synchronization device and the second time synchronization device via a first transmission device connected to the first time synchronization device and a second transmission device corresponding to the first transmission device and connected to the second time synchronization device,

• the transmission device being operable as the first transmission device or the second transmission device, comprising:
• a transmission section configured to transmit packets for delay calculation for a plurality of wavelengths to a corresponding transmission device simultaneously;
• and
• a reception section configured to:
• calculate a first propagation delay on a path from the corresponding transmission device to the transmission device based on a difference between arrival times of the packets for delay calculation for the plurality of wavelengths received from the corresponding transmission device,
• receive a second propagation delay on a path from the transmission device to the corresponding transmission device calculated by the corresponding transmission device, and
• calculate a set delay that is larger than any of the first propagation delay and the second propagation delay, wherein
• the reception section is further configured to:
• calculate a third propagation delay on the path from the corresponding transmission device to the transmission device based on a difference between arrival times of the packets for time synchronization for the plurality of wavelengths when the packets for time synchronization are received from the corresponding transmission device, and
• transmit the received packets for time synchronization to the time synchronization device to which the transmission device is connected after waiting for a waiting delay that is calculated by subtracting the third propagation delay from the set delay, and
• wherein
• the second time synchronization device is configured to calculate an offset value that is a difference between a clock of the first time synchronization device and a clock of the second time synchronization device by using transmit times and receive times of the packets for time synchronization at the time synchronization devices.

A delay correction method implemented by a time transmission system, the time transmission system synchronizing time of a second time synchronization device based on time information of transmission and reception of packets for time synchronization between a first time synchronization device and the second time synchronization device via a first transmission device connected to the first time synchronization device and a second transmission device corresponding to the first transmission device and connected to the second time synchronization device, each of the first transmission device and the second transmission device comprising:

• a transmission section configured to transmit packets for delay calculation for a plurality of wavelengths to a corresponding transmission device simultaneously;
• and
• a reception section configured to:
• calculate a first propagation delay on a path from the corresponding transmission device to the transmission device based on a difference between arrival times of the packets for delay calculation for the plurality of wavelengths received from the corresponding transmission device,
• receive a second propagation delay on a path from the transmission device to the corresponding transmission device calculated by the corresponding transmission device, and
• calculate a set delay that is larger than any of the first propagation delay and the second propagation delay, wherein
• the reception section is further configured to:
• calculate a third propagation delay on the path from the corresponding transmission device to the transmission device based on a difference between arrival times of the packets for time synchronization for the plurality of wavelengths when the packets for time synchronization are received from the corresponding transmission device, and
• transmit the received packets for time synchronization to the time synchronization device to which the transmission device is connected after waiting for a waiting delay that is calculated by subtracting the third propagation delay from the set delay.