DOCSIS R-PHY without PTP
Synchronizing clocks across a Remote PHY network without use of the Precision Time Protocol (PTP). The clock used by the CCAP core may be referred to herein as a slave clock, while the clock used by each RPD may be referred to as a master clock. Time differences between each master clock and a slave clock in the Remote PHY network are tracked. Slave clocks at the core may, but need not, lock to a single RPD master clock. A CCAP core tracks differences in clock values between a singular CCAP core clock and one or more RPD clocks using clock values identified by received DEPI Latency Measurement (DLM) packets and not using Precision Time Protocol (PTP) protocol. The CCAP core determines a particular RPD clock value to use in sending a map message to a particular RPD. The CCAP core then sends a map message to the particular RPD over the network based on the determined particular RPD clock value.
1 . A non-transitory computer-readable storage medium storing one or more sequences of instructions for tracking time differences between a master clock and a slave clock, which when executed, cause:
at a Converged Cable Access Platform (CCAP) core, tracking differences in clock values between a singular CCAP core clock and one or more remote-PHY device (RPD) clocks using clock values identified by received Downstream External PHY Interface (DEPI) Latency Measurement (DLM) packets and not using Precision Time Protocol (PTP) protocol;
determining a particular RPD clock value to use in sending a map message to a particular RPD; and
sending the map message from the CCAP core to the particular RPD over a network based on said determined particular RPD clock value.
2 . The non-transitory computer-readable storage medium of claim 1 , wherein said determining said particular RPD clock value is performed using an estimate of network latency between said CCAP core and the particular RPD obtained using data obtained using DLM packets.
3 . The non-transitory computer-readable storage medium of claim 1 , wherein each of said one or more RPD clocks do not synchronize their clock values to clock values of any other clock.
4 . The non-transitory computer-readable storage medium of claim 1 , wherein determining a particular RPD clock value is performed using a measurement of network latency between said CCAP core and said particular RPD.
5 . The non-transitory computer-readable storage medium of claim 1 , wherein all of said one or more RPD clocks operate in a different clock domain than said singular CCAP core clock.
6 . The non-transitory computer-readable storage medium of claim 1 , wherein determining the particular RPD clock value comprises determining an estimate of network latency using two DLM Response packets sent by the particular RPD in response to two consecutive DLM Request packets.
7 . The non-transitory computer-readable storage medium of claim 1 , wherein determining the particular RPD clock value to use in sending the map message the particular RPD is performed using samples of a single offset value that represent (i) a measure of network latency and (ii) a clock phase offset between (a) said particular RPD clock and said singular CCAP core clock or (b) a clock used by software executing at said CCAP core and said particular RPD clock.
8 . The non-transitory computer-readable storage medium of claim 1 , wherein said determining said particular RPD clock value is performed using an estimate of network latency that is measured only in a downstream direction.
9 . An apparatus for tracking time differences between a master clock and a slave clock, comprising:
one or more processors; and
one or more non-transitory computer readable storage mediums storing one or more sequences of instructions, which when executed, cause:
at a Converged Cable Access Platform (CCAP) core, tracking differences in clock values between a singular CCAP core clock and one or more remote-PHY device (RPD) clocks using clock values identified by received Downstream External PHY Interface (DEPI) Latency Measurement (DLM) packets and not using Precision Time Protocol (PTP) protocol;
determining a particular RPD clock value to use in sending a map message to a particular RPD; and
sending the map message from the CCAP core to the particular RPD over a network based on said determined particular RPD clock value.
10 . The apparatus of claim 9 , wherein said determining said particular RPD clock value is performed using an estimate of network latency between said CCAP core and the particular RPD obtained using data obtained using DLM packets.
11 . The apparatus of claim 9 , wherein each of said one or more RPD clocks do not synchronize their clock values to clock values of any other clock.
12 . The apparatus of claim 9 , wherein determining a particular RPD clock value is performed using a measurement of network latency between said CCAP core and said particular RPD.
13 . The apparatus of claim 9 , wherein all of said one or more RPD clocks operate in a different clock domain than said singular CCAP core clock.
14 . The apparatus of claim 9 , wherein determining the particular RPD clock value comprises determining an estimate of network latency using two DLM Response packets sent by the particular RPD in response to two consecutive DLM Request packets.
15 . The apparatus of claim 9 , wherein determining the particular RPD clock value to use in sending the map message the particular RPD is performed using a single offset value to that represents clock phase offset between said particular RPD clock and said singular CCAP core clock and an estimate of network latency between said CCAP core and the particular RPD as measured in only a downstream direction.
16 . The apparatus of claim 9 , wherein said determining said particular RPD clock value is performed using an estimate of network latency that is measured only in a downstream direction.
17 . A method for tracking time differences between a master clock and a slave clock, comprising:
at a Converged Cable Access Platform (CCAP) core, tracking differences in clock values between a singular CCAP core clock and one or more remote-PHY device (RPD) clocks using clock values identified by received Downstream External PHY Interface (DEPI) Latency Measurement (DLM) packets and not using Precision Time Protocol (PTP) protocol;
the CCAP core determining a particular RPD clock value to use in sending a map message to a particular RPD; and
the CCAP core sending the map message to the particular RPD over a network based on said determined particular RPD clock value.
18 . The method of claim 17 , wherein the CCAP core determining said particular RPD clock value is performed using an estimate of network latency between said CCAP core and the particular RPD obtained using data obtained using DLM packets.
19 . The method of claim 17 , wherein each of said one or more RPD clocks do not synchronize their clock values to clock values of any other clock.
20 . The method of claim 17 , wherein determining a particular RPD clock value is performed using a measurement of network latency between said CCAP core and said particular RPD.
21 . The method of claim 17 , wherein all of said one or more RPD clocks operate in a different clock domain than said singular CCAP core clock.
22 . The method of claim 17 , wherein the CCAP core determining the particular RPD clock value comprises determining an estimate of network latency using two DLM Response packets sent by the particular RPD in response to two consecutive DLM Request packets.
23 . The method of claim 17 , wherein the CCAP core determining the particular RPD clock value to use in sending the map message the particular RPD is performed using a single offset value to that represents clock phase offset between said particular RPD clock and said singular CCAP core clock and an estimate of network latency between said CCAP core and the particular RPD as measured in only a downstream direction.
24 . The method of claim 17 , wherein said determining said particular RPD clock value is performed using an estimate of network latency that is measured only in a downstream direction.