US 12,225,103 B2
Time synchronization system, receiving server and time synchronization method
Kei Fujimoto, Musashino (JP); Masashi Kaneko, Musashino (JP); and Takeshi Fukumoto, Musashino (JP)
Assigned to Nippon Telegraph and Telephone Corporation, Tokyo (JP)
Appl. No. 18/025,512
Filed by Nippon Telegraph and Telephone Corporation, Tokyo (JP)
PCT Filed Sep. 15, 2020, PCT No. PCT/JP2020/034811
§ 371(c)(1), (2) Date Mar. 9, 2023,
PCT Pub. No. WO2022/059049, PCT Pub. Date Mar. 24, 2022.
Prior Publication US 2024/0014999 A1, Jan. 11, 2024
Int. Cl. H04Q 11/00 (2006.01); H04B 10/073 (2013.01); H04J 3/06 (2006.01); H04L 7/00 (2006.01)
CPC H04L 7/0075 (2013.01) [H04B 10/073 (2013.01); H04J 3/0638 (2013.01); H04Q 11/0062 (2013.01); H04Q 2011/0045 (2013.01); H04Q 2011/0079 (2013.01); H04Q 2213/13214 (2013.01); H04Q 2213/36 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A time synchronization system comprising:
a queueless network (NW) formed by connecting a plurality of optical cross connects (OXCs) by optical fibers, each of the plurality of OXCs configured to perform switching processing of performing transmission of an optical signal while switching the optical signal to a destination route in the form of light; and
an NW controller, a plurality of transmitting servers, and a receiving server, which are connected to the queueless NW so as to be able to transmit an optical signal,
wherein the NW controller is configured to, for each of the plurality of transmitting servers, perform processing of setting, based on NW topology information related to the queueless NW, transmission distance information on a transmission distance through which an optical signal is transmitted from the transmitting server to the receiving server via the queueless NW to the receiving server,
wherein each of the plurality of transmitting servers is configured to perform processing of:
receiving a reference time that ticks at regular intervals;
generating reference time information based on a transmitting side current time synchronized with the received reference time; and
transmitting an optical signal on which the generated reference time information is superimposed to the receiving server via the queueless NW, and
wherein the receiving server is configured to perform processing of:
for each of the plurality of transmitting servers, after receiving the reference time information from the transmitting server, dividing the transmission distance, which is based on the transmission distance information set by the NW controller for the transmitting server, by a light speed, which is an optical signal speed in the queueless NW, to calculate a transmission delay time between the transmitting server and the receiving server;
for each of the plurality of transmitting servers, adding the calculated transmission delay time of the transmitting server to the transmitting side current time, which is based on the reference time information of the transmitting server, to calculate a receiving side current time related to the transmitting server; and
detecting that, regarding the calculated receiving side current time related to one transmitting server of the plurality of transmitting servers, when a time difference between a receiving side current time calculated this time for the one transmitting server and a receiving side current time calculated last time for the one transmitting server differs from a time difference between the receiving side current time calculated last time for the one transmitting server and a receiving side current time calculated at a time preceding the last time for the one transmitting server by a predetermined threshold value or more, the receiving side current time calculated this time is abnormal.