Systems and methods to improve holdover performance in R-PHY network architectures
Systems and methods for regaining synchronization between a CMTS core and an RPD, where both the core and the RPD are configured for individual synchronization in a slave configuration to a common grandmaster clock.
1. A system comprising:
a Cable Modem Termination System (CMTS) core having a first slave clock configured to be synchronized with a grandmaster timer;
a Remote Physical Device (RPD) having a second slave clock configured to be synchronized with the grandmaster timer; where
at least one of the core and the RPD is configured to regain phase synchronization with the grandmaster timer, after losing synchronization with the grandmaster timer, by automatically and selectively implementing a gradual change in a frequency difference relative to the grandmaster over a period of time, selection based on timing data exchanged between the core and the RPD.
2. The system of claim 1 where the RPD is configured to regain synchronization with the grandmaster timer, after losing synchronization with the grandmaster timer, based on timing data exchanged between the core and the RPD.
3. The system of claim 1 where the RPD is configured to regain synchronization with the grandmaster timer, after losing synchronization with the grandmaster timer, based on timing data exchanged between the core and the RPD.
4. The system of claim 1 where synchronization is regained with the grandmaster timer by a phase step when the gradual change in a frequency difference relative to the grandmaster timer over a period of time is not selected.
5. The system of claim 4 where selection is based on at least one of: (a) the core's measured offset from the grandmaster; (b) the RPD's measured offset from the grandmaster; (c) a respective state of at least one cable modem connected to the RPD; and (d), a the currently configured MAP advance time from the core to the RPD.
6. The system of claim 1 where the core changes its MAP advance time to the RPD based on a message from the RPD.
7. The system of claim 1 in an R-PHY architecture.
8. A method used in a Remote Physical (R-PHY) architecture to recover synchronization between a Cable Modem Termination System (CMTS) core and a Remote Physical Device (RPD), where both the core and the RPD are configured for individual synchronization in a slave configuration to a common grandmaster clock, the method comprising:
a first one of the core and the RPD renewing synchronization with the grandmaster clock;
exchanging at least one timing parameter between the core and the RPD; and
the first one of the core and the RPD using the at least one timing parameter to regain synchronization with the grandmaster clock by automatically selecting an alternative one of a phase shift and a gradual change in a frequency difference relative to the grandmaster timer over a period of time.
9. The method of claim 8 where the RPD regains synchronization with the grandmaster clock.
10. The method of claim 8 where the core regains synchronization with the grandmaster clock.
11. The method of claim 8 where the at least one timing parameter includes at least one of: (a) the core's measured offset from the grandmaster; (b) the RPD's measured offset from the grandmaster; (c) a respective state of at least one cable modem connected to the RPD; and (d), a the currently configured MAP advance time from the core to the RPD.
12. The method of claim 8 including the steps of: (a) receiving status information of a plurality of cable modems attached to the RPD; (b) comparing a threshold to the status information; and (c) selectively performing a phase step adjustment based on the comparison.
13. The method of claim 8 including the steps of: comparing a phase offset relative to the grandmaster clock to a threshold; and (b) selectively performing a gradual change in a frequency difference relative to the grandmaster timer over a period of time.
14. The method of claim 8 including the steps of: (a) receiving a phase offset value relative to the grandmaster timer; and (b) determining whether the core can change a MAP advance time based on the phase offset.
15. The method of claim 14 including the steps of: changing the MAP advance time; and selectively performing a gradual change in a frequency difference relative to the grandmaster timer over a period of time.