Systems and methods for transporting time-of-day information in a communication system
View Patent ↗Systems and methods for synchronizing a clock at a customer premises equipment (CPE) location with a master clock at a central office (CO) location are described. One embodiment is a method that comprises receiving, by a time-of-day transmission convergence (ToD-TC) module in the CPE, ToD information relating to the master clock. Based on the received information, time stamps are applied to reference data samples. The method further comprises transporting the ToD information by transporting the reference data samples with applied time stamps and utilizing time stamps of the reference data samples to synchronize the CPE clock with the master clock.
1. A method for synchronizing a clock at a customer premises equipment (CPE) location with a master clock at a central office (CO) location, comprising:
receiving, by a time-of-day transmission convergence (ToD-TC) module in the CO, ToD information relating to the master clock;
transporting the ToD information from the CO to the CPE;
based on the received ToD information, applying time stamps to reference data samples;
transporting the reference data samples with the applied time stamps from the CO to the CPE; and
utilizing the time stamps applied to the transported reference data samples and the transported ToD information to synchronize the CPE clock with the master clock.
2. The method of claim 1 , wherein synchronizing comprises:
synchronizing a frequency of the CPE clock with respect to the master clock; and
synchronizing a phase of the CPE clock with respect to the master clock.
3. The method of claim 1 , wherein transporting the ToD information is performed via an embedded operations channel (EOC) between the CO and CPE.
4. The method of claim 1 , wherein the information received by the ToD-TC comprises:
a master clock edge, a master clock value associated with the master clock edge, and a master clock frequency, wherein the master clock edge is synchronous to the master clock frequency.
5. The method of claim 1 , wherein the ToD information is synchronous to the master clock.
6. The method of claim 1 , wherein the master clock in the CO is synchronous to a grandmaster clock.
7. The method of claim 1 , wherein utilizing time stamps of the reference data samples to synchronize the CPE clock with the master clock comprises:
receiving, at the CPE, the reference data samples with time stamps and deriving timing based on the time stamps; and
based on the time stamps, synchronizing the CPE clock with the master clock with respect to frequency and phase.
8. The method of claim 7 , wherein synchronizing with respect to frequency comprises synchronizing the frequency of the CPE clock using a loop timing block at the CPE based on the master clock frequency.
9. The method of claim 8 , wherein using a loop timing block comprises using a phase lock loop (PLL) to synchronize the CPE clock with the master clock based on the reference samples with time stamps.
10. The method of claim 7 , wherein synchronizing with respect to frequency comprises synchronizing based on phase difference values received from the CO over an embedded operations channel (EOC).
11. The method of claim 10 , wherein the phase difference value comprises a compressed size of two bytes and is received from the CO approximately once every discrete multi-tone (DMT) super-frame.
12. The method of claim 10 , wherein the phase difference value comprises fixed bytes in an overhead (OH) frame.
13. The method of claim 7 , wherein synchronizing with respect to time and phase comprises determining an average offset based on time stamps generated by the CO and time stamps generated by the CPE, wherein the phase of the CPE clock is adjusted according to the average offset.
14. The method of claim 1 , wherein applying time stamps to reference data samples is performed based on a first data sample or other reference sample established between the CO and the CPE following a synch symbol in a discrete multi-tone (DMT) sequence transmitted between the CO and CPE.
15. The method of claim 14 , wherein applying time stamps to reference data samples is performed once every DMT super-frame.
16. A method for synchronizing a clock at a customer premises equipment (CPE) location with a master clock at a central office (CO) location, comprising:
receiving, by a time-of-day transmission convergence (ToD-TC) module at the CO, time-of-day (ToD) information relating to the master clock;
transporting the ToD information to the CPE;
based on the received information, applying time stamps to reference data samples once every discrete multi-tone (DMT) super-frame;
transporting the reference data samples with applied time stamps to the CPE; and
utilizing, by a time-of-day transmission convergence (ToD-TC) module at the CPE, time stamps of the reference data samples and the transported ToD information to synchronize the CPE clock with the master clock with respect to frequency and phase.
17. The method of claim 16 , wherein transporting the reference data samples with applied time stamps to the CPE comprises encoding ToD phase difference information in a frequency synchronization command.
18. The method of claim 17 , wherein the frequency synchronization command comprises a downstream time stamp.
19. The method of claim 18 , wherein the frequency synchronization command further comprises a one byte index identifying a specific superframe corresponding to a phase drift value being sent and two bytes specifying the phase drift value.
20. A system for synchronizing a clock at a customer premises equipment (CPE) location with a master clock at a central office (CO) location, comprising:
a first time-of-day transmission convergence (ToD-TC) module at the CO configured to receive time-of-day (ToD) information relating to the master clock, the first ToD-TC module further configured to time stamp reference data samples and transmit the ToD information and the time stamped reference data samples to the CPE;
a second ToD-TC module at the CPE configured to receive the ToD information and the time stamp reference data samples from the first ToD-TC module and synchronize the CPE clock with the master clock based on the received ToD information and the time stamped reference data samples.
21. The system of claim 20 , wherein the first ToD-TC module performs time stamping of reference data samples using a time stamping clock synchronized to an external clock at the CO.
22. The system of claim 20 , wherein the first ToD-TC module is configured to transmit a 2-byte drift value over an embedded operations channel EOC to the second ToD-TC module, wherein based on the 2-byte drift value, the second ToD-TC module synchronizes the CPE clock with the master clock with respect to phase.
23. The system of claim 20 , wherein the second ToD-TC module monitors a time difference between successive reference data samples and adjusts a time difference between successive reference data samples sent to the CO such that the time differences is approximately zero.