Time synchronization device, time synchronization system, and recording medium

A time synchronization system, comprising:

• a time retaining device to retain a time;
• a first time synchronization device connected to the time retaining device;
• and
• a second time synchronization device connected to the first time synchronization device, wherein
• the first time synchronization device and the second time synchronization device execute time synchronization with the time retaining device,
• the first time synchronization device comprises:
• a first synchronization information receiver to receive synchronization information on time synchronization transmitted from the time retaining device;
• a first request information transmitter to transmit, to the time retaining device, request information that is based on the synchronization information received by the first synchronization information receiver;
• a first response information receiver to receive response information transmitted from the time retaining device having received the request information;
• a first time corrector to execute time correction based on a propagation delay time between the time retaining device and the first time synchronization device, the propagation delay time being calculated from times identified through transmission and reception of information to and from the time retaining device via the first synchronization information receiver, the first request information transmitter, and the first response information receiver;
• a first synchronization information transmitter to transmit synchronization information to the second time synchronization device;
• a first request information receiver to receive request information, the request information being transmitted from the second time synchronization device after transmission of the synchronization information from the first synchronization information transmitter;
• and
• a first response information transmitter to transmit, to the second time synchronization device, response information responding to the request information received by the first request information receiver,
• the second time synchronization device comprises:
• a second synchronization information receiver to receive the synchronization information transmitted from the first synchronization information transmitter;
• a second request information transmitter to transmit, to the first time synchronization device, the request information that is based on the synchronization information received by the second synchronization information receiver;
• a second response information receiver to receive the response information transmitted from the first response information transmitter;
• and
• a second time corrector to execute time correction based on a propagation delay time between the first time synchronization device and the second time synchronization device, the propagation delay time being calculated from times identified through transmission and reception of information to and from the first time synchronization device via the second synchronization information receiver, the second request information transmitter, and the second response information receiver, and
• the first time synchronization device does not execute time correction during a predetermined period from transmission of the synchronization information from the first synchronization information transmitter until reception of the request information by the first request information receiver even when information is received from or transmitted to the time retaining device.

A non-transitory computer-readable recording medium storing a program, the program causing a computer to function as:

• a synchronization information transmitter to transmit synchronization information on time synchronization to another time synchronization device, the another time synchronization device being not connected to a time retaining device retaining a time, the another time synchronization device being configured to execute time synchronization with the time retaining device;
• a request information receiver to receive request information that is based on the synchronization information, the request information being transmitted from the another time synchronization device after transmission of the synchronization information from the synchronization information transmitter;
• a response information transmitter to transmit, to the another time synchronization device, response information responding to the request information received by the request information receiver;
• and
• a time corrector (i) to execute time correction based on a propagation delay time between the time retaining device and the computer during a period different from a predetermined period from transmission of the synchronization information from the synchronization information transmitter until reception of the request information by the request information receiver, the propagation delay time being calculated from times identified through transmission and reception of information to and from the time retaining device, and (ii) not to execute time correction during the predetermined period even when information is received from or transmitted to the time retaining device.