Patent ID: 9264213
Filing Date: 2016-02-16
CPC Classification: H04B,H04J,H04L,H04Q

Claim Text:
1. A time synchronization method for a communication system configured to perform protection switching, the communication system including a first network in which an OLT (Optical Line Terminal) and an ONU (Optical Network Unit) are connected via a plurality of physical lines including a working line and a backup line and a second network connected to the ONU, the time synchronization method comprising: a step in which the OLT transmits a synchronization signal to the ONU and the ONU synchronizes a clock of the ONU with a clock of the OLT using the received synchronization signal; a step in which the OLT transmits a synchronization command including designated time information and timing information to the ONU; a switching step for performing a protection switching in which the OLT uses, when detecting a communication failure of an uplink signal in the working line, the backup line as a new working line instead of the working line; and a time synchronization step in which the ONU executes, when not detecting a switching condition for the protection switching based on a downlink signal transmitted from the OLT, synchronization processing for correcting the time information included in the synchronization command based on the clock of the ONU and the timing information and transmitting the synchronization command to the second network and executing, when detecting the switching condition for the protection switching or receiving a switching notification from the OLT, processing for suppressing a synchronization error due to a difference between the clock of the ONU and the timing information.