SYNCHRONIZATION TRANSPORT OVER PASSIVE OPTICAL NETWORKS

• US 20100098433A1
• Filed: 10/06/2009
• Published: 04/22/2010
• Est. Priority Date: 10/21/2008
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Teknovus Inc. (Broadcom, Inc.)
• Inventors: Shibuya, Hidehiko, Boyd, Edward W.
• Granted Patent: US 8,942,561 B2
• Time in Patent Office: Days
• US Class Current: 398/155
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04Q 11/0067 Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
• CPC Class Codes: H04Q 2011/0079 Operation or maintenance aspects

Abstract

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.

Claims

1. An Ethernet Passive Optical Network (EPON) system for clock transport, comprising:

a reference clock configured to generate a frequency-reference signal;

an optical line terminal (OLT) coupled to the reference clock, wherein the OLT comprises a clock generator configured to generate an OLT clock based on at least the frequency-reference signal; and

an optical network unit (ONU), the ONU comprising;

an optical transceiver configured to transmit optical signals to and receive optical signals from the OLT;

a clock-recovery module configured to recover the frequency-reference signal from the received optical signals; and

a clock output mechanism configured to output the recovered frequency-reference signal, thus facilitating transport of the frequency-reference signal over the EPON.

2. The system of claim 1, wherein the optical transceiver comprises the clock-recovery module.

3. The system of claim 1, wherein the reference clock is further configured to generate a phase-reference signal, which can be used to obtain phase synchronization between the recovered frequency-reference signal and the original frequency-reference signal.

4. The system of claim 3, wherein the OLT is configured to receive the phase-reference signal and communicate phase information associated with the phase-reference signal to the ONU, and wherein the ONU is configured to synchronize the phase of the recovered frequency-reference signal to the phase of the phase-reference signal.

5. The system of claim 4, wherein while communicating the phase information, the OLT is configured to broadcast the phase information in an Operation Administration Management (OAM) message, and wherein the OAM message comprises a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal.

6. The system of claim 5, 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.

7. The system of claim 6, wherein the ONU further comprises a 1 PPS pulse generator configured to generate 1 PPS pulses, and wherein an edge of the ONU-generated 1 PPS pulses is aligned to the MPCP time plus a predetermined adjustment amount.

8. The system of claim 3, wherein the ONU is configured to adjust the received phase-reference signal by compensating for at least one of:

propagation delay between the OLT and the ONU;

delay incurred to the phase-reference signal on the OLT; and

delay incurred to the phase-reference signal on the ONU.

9. The system of claim 1, wherein the OLT is configured to communicate a time-of-day (TOD) value to the ONU via an OAM message.

10. An optical line terminal (OLT) for clock transport in an Ethernet Passive Optical Network (EPON), comprising:

a clock generator coupled to a reference clock and configured to generate an OLT clock based at least on a frequency-reference signal corresponding to the reference clock; and

an optical transceiver coupled to the clock generator and configured to transmit the OLT clock signal to a downstream optical network terminal (ONU).

11. The OLT of claim 10, further comprising a phase-synchronization mechanism coupled to the reference clock and configured to receive a phase-reference signal associated with the frequency-reference signal.

12. The OLT of claim 11, wherein the phase-synchronization mechanism is configured to communicate phase information associated with the phase-reference signal to the ONU.

13. The OLT of claim 12, wherein while communicate the phase information, the phase-synchronization mechanism is configured to broadcast the phase information in an Operation Administration Management (OAM) message, and wherein the OAM message comprises a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal.

14. The OLT of claim 13, 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.

15. The OLT of claim 10, wherein the optical transceiver is configured to communicate a time-of-day (TOD) value to the ONU via an OAM message.

16. An optical network unit (ONU) for clock transport in an Ethernet Passive Optical Network (EPON), comprising:

an optical transceiver configured to transmit optical signals to and receive optical signals from an upstream optical line terminal (OLT);

a clock-recovery module coupled to the optical transceiver and configured to;

recover a frequency-reference signal from the received optical signals, and coupled to the OLT; and

receive phase information associated with a phase-reference signal from an Operation Administration Management (OAM) message broadcast by the OLT; and

a clock output mechanism configured to output the recovered frequency-reference signal, thus facilitating transport of the frequency-reference signal over the EPON.

17. The ONU of claim 16, further comprising a phase reference mechanism configured to output a phase-reference signal based at least on the recovered phase information.

18. The ONU of claim 17, wherein the OAM message comprises a count number indicating a Multipoint Control Protocol (MPCP) time corresponding to the phase-reference signal.

19. The ONU of claim 18, 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.

20. The ONU of claim 19, wherein the phase comprising a 1 PPS pulse generator configured to generate 1 PPS pulses, wherein an edge of the ONU-generated 1 PPS pulses is aligned to the MPCP time plus a predetermined adjustment amount based at least on the recovered phase information.

21. The ONU of claim 17, wherein the phase reference mechanism is configured to adjust the phase-reference signal by compensating for at least one of:

propagation delay between the OLT and the ONU;

delay incurred to a corresponding phase-reference signal on the OLT; and

delay incurred to a corresponding phase-reference signal on the ONU.

22. The ONU of claim 16, wherein the optical transceiver is configured to receive a time-of-day (TOD) value from the OLT via an OAM message.

23. A method for transmitting a clock in an Ethernet Passive Optical Network (EPON), comprising:

providing a frequency-reference signal to an optical line terminal (OLT);

generating an OLT clock based at least on the frequency-reference signal; and

transmitting the OLT clock to a downstream optical network unit (ONU).

24. A method for receiving a clock in an Ethernet Passive Optical Network (EPON), comprising:

receiving optical signals from an optical line terminal (OLT);

recovering a frequency-reference signal from the received optical signals;

receiving phase information associated with a phase-reference signal from an Operation Administration Management (OAM) messagebroadcast by the OLT; and

generating an output based at least on the recovered frequency-reference signal.