Patent ID: 8335437

Claim:
A time synchronization method in a passive optical network (PON), the PON comprising an optical line terminal (OLT) and a plurality of optical network units (ONUs), the method comprising: receiving, by an ONU, a synchronization packet sent by the OLT after a time synchronization of the OLT with a master clock (MC) is achieved, wherein the synchronization packet comprises a timestamp TMt 1 i and a frame sequence number of a first downlink frame, wherein the timestamp TMt 1 i is equal to TMt 1 +Tdi when the synchronization packet is a unicast packet, wherein TMt 1 is an OLT time when the OLT sends the synchronization packet and Tdi is a downlink delay from the OLT to the ONU; wherein the frame sequence number of the first downlink frame is a value obtained from an OLT superframe counter in a Gigabit PON (GPON) or a value obtained from an OLT timestamp counter in an Ethernet passive optical network (EPON); adjusting, by the ONU, a local clock according to the timestamp TMt 1 i and the frame sequence number of the first downlink frame to achieve the time synchronization of the ONU with the OLT; and instructing, by the ONU, a slave clock (SC) to perform a time synchronization with the ONU.