Synchronization transport over passive optical networks
View Patent ↗One embodiment provides an Ethernet Passive Optical Network (EPON) system for clock transport. The system includes a reference clock configured to generate a frequency-reference signal, an optical line terminal (OLT) coupled to the reference clock, and an optical network unit (ONU). The OLT includes a clock generator configured to generate an OLT clock based on at least the frequency-reference signal. The ONU includes an optical transceiver, a clock recovery module, and a clock output mechanism. The optical transceiver is configured to transmit optical signals to and receive optical signals from the OLT. The clock-recovery module is configured to recover the frequency-reference signal from the received optical signals. The clock output mechanism is configured to output the recovered frequency-reference signal, thus facilitating transport of the frequency-reference signal over the EPON.
1. An Ethernet Passive Optical Network (EPON) system for clock transport, comprising:
a reference clock configured to generate a frequency-reference signal and a phase-reference signal;
an optical line terminal (OLT) configured:
to generate an OLT clock based on and different from the frequency-reference signal, and
to transmit phase information relating to the frequency-reference signal in Operation Administration Management (OAM) message having a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal; and
an optical network unit (ONU) configured:
to recover the frequency-reference signal from the phase information,
to synchronize a phase of, the recovered frequency-reference signal to a phase of the phase-reference signal, and
to output the recovered frequency-reference signal to facilitate transport of the frequency-reference signal over the EPON system.
2. The system of claim 1 , wherein the phase-reference signal is a clock signal of 1 pulse-per-second (1 PPS), and
wherein the MPCP time corresponds to an edge of the 1 PPS clock signal.
3. The system of claim 2 , wherein the ONU further comprises:
a 1 PPS pulse generator configured to generate a 1 PPS pulse, and
wherein an edge of the generated 1 PPS pulse is aligned to the MPCP time plus a predetermined adjustment amount.
4. The system of claim 1 , wherein the ONU is further configured to adjust the phase-reference signal to compensate for at least one of:
propagation delay between the OLT and the ONU;
delay incurred to the phase-reference signal on the OLT; or
delay incurred to the phase-reference signal on the ONU.
5. The system of claim 1 , wherein the OLT is further configured to communicate a time-of-day (TOD) value to the ONU via the OAM message.
6. An optical line terminal (OLT) for clock transport in an Ethernet Passive Optical Network (EPON), comprising:
a clock generator, coupled to a reference clock, configured to generate an OLT clock based on a frequency-reference signal corresponding to the reference clock;
an optical transceiver, coupled to the clock generator, configured to transmit the OLT clock to a downstream optical network unit (ONU); and
a phase-synchronization mechanism, coupled to the reference clock, configured to receive a phase-reference signal associated with the frequency-reference signal and to broadcast the phase information in an Operation Administration Management (OAM) message having a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal.
7. The OLT of claim 6 , wherein the phase-reference signal is a clock signal of 1 pulse-per-second (1 PPS), and
wherein the MPCP time corresponds to an edge of the 1 PPS clock signal.
8. The OLT of claim 6 , wherein the optical transceiver is further configured to communicate a time-of-day (TOD) value to the ONU via the OAM message.
9. An optical network unit (ONU) for clock transport in an Ethernet Passive Optical Network (EPON), comprising:
an optical transceiver configured to receive an optical signal from an upstream optical line terminal (OLT);
a clock-recovery module, coupled to the optical transceiver, configured to:
recover a frequency-reference signal from the received optical signal, and
receive phase information associated with a phase-reference signal from an Operation Administration Management (OAM) message broadcast by the upstream OLT, the OAM message including a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal;
a phase reference mechanism configured to synchronize a phase of the recovered frequency-reference signal to a phase of the phase-reference signal based on the received phase information; and
a clock output mechanism configured to output the recovered frequency-reference signal to facilitate transport of the frequency-reference signal over the EPON.
10. The ONU of claim 9 , wherein the phase-reference signal is a clock signal of 1 pulse-per-second (1 PPS), and
wherein the MPCP time corresponds to an edge of the 1 PPS clock signal.
11. The ONU of claim 10 , wherein the ONU further comprises:
a 1 PPS pulse generator configured to generate a 1 PPS pulse,
wherein an edge of the generated 1 PPS pulse is aligned to the MPCP time plus a predetermined adjustment amount based on the recovered phase information.
12. The ONU of claim 9 , wherein the phase reference mechanism is further configured to adjust the phase-reference signal to compensate for at least one of:
propagation delay between the upstream OLT and the ONU;
delay incurred to a corresponding phase-reference signal on the upstream OLT; or
delay incurred to a corresponding phase-reference signal on the ONU.
13. The ONU of claim 9 , wherein the optical transceiver is further configured to receive a time-of-day (TOD) value from the upstream OLT via the OAM message.
14. A method for receiving a clock in an Ethernet Passive Optical Network (EPON), comprising:
receiving an optical signal from an optical line terminal (OLT);
recovering a frequency-reference signal from the received optical signal;
receiving phase information associated with a phase-reference signal from an Operation Administration Management (OAM) message broadcast by the OLT, the OAM message including a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal;
synchronizing a phase of the recovered frequency-reference signal to a phase of the phase-reference signal based on the received phase information; and
generating an output based on the recovered frequency-reference signal.
15. The system of claim 1 , wherein the phase information is a 1 pulse-per-second (1 PPS) signal and is transported from the OLT to the ONU via the OAM message.
16. The system of claim 1 , wherein the ONU is further configured to adjust a next pulse time to compensate for fiber propagation latency, OLT-side latency, and ONU side latency based on the received OAM message.
17. The system of claim 16 , wherein the ONU comprises:
a pulse generator configured to align a rising edge of a next pulse with a programmed pulse time stored in a register.