Communication system, communication system control method, transmission device, and reception device

A control method for a communication system, the communication system comprising:

• a transmission device that transmits a time synchronization packet for time synchronization;
• and a reception device that receives the time synchronization packet, the control method comprising:
• a first counting step of establishing, by the transmission device, synchronization with a second counter within the reception device and measuring, as a first count value, a timing before the time synchronization packet is input to for performing processing on the time synchronization packet;
• a multiplexing step of multiplexing, by the transmission device, the first count value into the time synchronization packet and transmitting the time synchronization packet to the reception device;
• a second counting step of measuring, by the reception device, a timing when performing processing on the time synchronization packet is completed, as a second count value;
• an extraction step of extracting, by the reception device, the first count value from the time synchronization packet;
• and
• a modification step of modifying, by the reception device, a delay amount field by calculating a modification value based on the second count value, the first count value, and a value of the delay amount field within the time synchronization packet, the value of the delay amount field indicating a total amount of delay in a relay device, wherein:
• when the first count value is greater than the second count value, the delay amount field is modified by using, as the modification value, a value obtained by subtracting the first count value from the value of the delay amount field and adding the second count value and a maximum count value of the second counter, and
• when the second count value is greater than the first count value, the delay amount field is modified by using, as the modification value, a value obtained by subtracting the first count value from the value of the delay amount field and adding the second count value.

A reception device that receives a time synchronization packet for time synchronization, the reception device comprising:

• a second counter that measures, as a second count value, a timing when performing processing on the time synchronization packet is completed;
• wherein the reception devices is configured to extract a first count value from the time synchronization packet;
• and
• wherein the reception devices is configured to modify a delay amount field by calculating a modification value based on the second count value, the first count value, and a value of the delay amount field within the time synchronization packet, the value of the delay amount field indicating a total amount of delay in a relay device, wherein:
• when the first count value is greater than the second count value, the reception device modifies the delay amount field by using, as the modification value, a value obtained by subtracting the first count value from the value of the delay amount field and adding the second count value and a maximum count value of the second counter, and
• when the second count value is greater than the first count value, the reception device modifies the delay amount field by using, as the modification value, a value obtained by subtracting the first count value from the value of the delay amount field and adding the second count value.