Time synchronization method and device in passive optical network and passive optical network

1. 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.

2. The method according to claim 1 , wherein the ONU adjusts the 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 comprises:

recording, by the ONU, a corresponding relation between the frame sequence number of the first downlink frame and an ONU time when the ONU receives the first downlink frame;

finding, by the ONU, the corresponding relation to obtain the ONU time when the ONU receives the first downlink frame according to the frame sequence number of the first downlink frame in the synchronization packet; and

adjusting, by the ONU, the local clock according to the timestamp TMt 1 i and the ONU time.

3. The method according to claim 1 , wherein the synchronization packet is based on the a Physical Layer Operation, Administration, and Management (PLOAM) protocol, or an ONU Management and Control Interface (OMCI) protocol, or an EPON Multi-Point Control Protocol (MPCP).

4. The method according to claim 1 , wherein the first downlink frame comprises a header portion and a data payload portion, the synchronization packet is configured at the header portion of the first downlink frame, and the header portion of the first downlink frame comprises a GPON Encapsulation Method (GEM) header or an EPON preamble.

5. A time synchronization device in a passive optical network (PON), comprising:

a receiving unit, configured to receive a synchronization packet sent by an 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 an optical network unit (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);

an adjusting unit, configured to adjust 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

an instructing unit, configured to instruct a slave clock (SC) to perform a time synchronization with the ONU.

6. The device according to claim 5 , wherein the device further comprising:

a time obtaining unit, configured to record a corresponding relationship between the frame sequence number of the first downlink frame and an ONU time when the ONU receives the first downlink frame, find the corresponding relationship to obtain the ONU time when the ONU receives the first downlink frame according to the frame sequence number of the first downlink frame carried in the synchronization packet;

wherein the adjusting unit is further configured to adjust the local clock according to the timestamp TMt 1 i and the ONU time.

7. The device according to claim 5 , wherein the synchronization packet is based on the a Physical Layer Operation, Administration, and Management (PLOAM) protocol, or an ONU Management and Control Interface (OMCI) protocol, or an EPON Multi-Point Control Protocol (MPCP).

8. The device according to claim 5 , wherein the first downlink frame comprises a header portion and a data payload portion, the synchronization packet is configured at the header portion of the first downlink frame, and the header portion of the first downlink frame comprises a GPON Encapsulation Method (GEM) header or an EPON preamble.

9. An optical line terminal (OLT), comprising:

a synchronizing unit, configured to achieve a time synchronization with a master clock (MC); a time obtaining module, configured to determine a timestamp TMt 1 i after the time synchronization is achieved, wherein the timestamp TMt 1 i is equal to TMt 1 +Tdi when a 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 an optical network unit ONU;

a counter, configured to obtain a value from a superframe count of a Gigabit PON (GPON) or a timestamp count of an Ethernet passive optical network (EPON);

a packet generating module, configured to generate the synchronization packet and send the synchronization packet to a downlink sending module, wherein the synchronization packet comprises the timestamp TMt 1 i and a frame sequence number of a first downlink frame, wherein the frame sequence number of the first downlink frame is a value obtained from the counter; and

the downlink sending module, configured to send the synchronization packet generated by the packet generating module to the ONU, for the ONU to adjust a local clock according to the timestamp TMt 1 i and the frame sequence number of the first downlink frame.

10. The OLT according to claim 9 , wherein the synchronization packet is based on the a Physical Layer Operation, Administration, and Management (PLOAM) protocol, or an ONU Management and Control Interface (OMCI) protocol, or an EPON Multi-Point Control Protocol (MPCP).

11. The OLT according to claim 9 , wherein the first downlink frame comprises a header portion and a data payload portion, the synchronization packet is configured at the header portion of the downlink frame, and the header portion of the downlink frame comprises a GPON Encapsulation Method (GEM) header or an EPON preamble.

12. A passive optical network (PON), comprising: an optical line terminal (OLT) and a plurality of optical network units (ONUs), wherein:

the OLT is configured to achieve a time synchronization with a master clock (MC), and send a synchronization packet to an ONU, wherein the synchronization packet carries a timestamp TMt 1 i and a frame sequence number of a first downlink frame, wherein the timestamp TMt 1 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); and

the ONU is configured to receive the synchronization packet, adjust 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 instruct a slave clock (SC) to perform time synchronization with the ONU.

13. The PON according to claim 12 , wherein the ONU is configured to record a corresponding relation between the frame sequence number of the first downlink frame and an ONU time when the ONU receives the first downlink frame; find the corresponding relation to obtain the ONU time when the ONU receives the first downlink frame according to the frame sequence number of the first downlink frame in the synchronization packet; and adjust the local clock according to the timestamp TMt 1 i and the ONU time.

14. The PON according to claim 12 , wherein the synchronization packet is based on the a Physical Layer Operation, Administration, and Management (PLOAM) protocol, or an ONU Management and Control Interface (OMCI) protocol, or an EPON Multi-Point Control Protocol (MPCP).

15. The PON according to claim 12 , wherein the first downlink frame comprises a header portion and a data payload portion, the synchronization packet is configured at the header portion of the first downlink frame, and the header portion of the first downlink frame comprises a GPON Encapsulation Method (GEM) header or an EPON preamble.