Managing time offset and frequency drift in asynchronous DOCSIS remote PHY network environments

• US 9,722,739 B2
• Filed: 04/13/2015
• Issued: 08/01/2017
• Est. Priority Date: 04/14/2014
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Liu, Tong, Jin, Hang, Tang, Yi, Su, Lin, Chapman, John T.
• Primary Examiner(s): Bednash, Joseph
• Assistant Examiner(s): Cunningham, Kevin
• Application Number:
  US14/685,403
• Publication Number:
  US 20150295669A1
• Time in Patent Office: 841 Days
• CPC Class Codes: H04B 3/542 the information being in digital form
• 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: H04J 3/0673 using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 27/2697 in combination with other modulation techniques
• CPC Class Codes: H04L 27/3405 Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
• CPC Class Codes: H04L 27/345 Modifications of the signal space to allow the transmission of additional information
• CPC Class Codes: H04L 47/12 Avoiding congestion; Recovering from congestion
• CPC Class Codes: H04L 47/27 Evaluation or update of window size, e.g. using information derived from acknowledged [ACK] packets
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling

Abstract

An example method for managing time offset and frequency drift in asynchronous Data Over Cable Service Interface Specification (DOCSIS) Remote Physical layer (R-PHY) network environments is provided and includes receiving, at a first hardware device, time synchronization message from a remote second hardware device in the DOCSIS R-PHY network, determining a time difference between a first clock at the first hardware device and a second clock at the second hardware device from the time synchronization message; and re-stamping an event message based on the time difference.

Claims

1. A method comprising:

receiving, at a first hardware device, a time synchronization message from a remote second hardware device in a Data Over Cable Service Interface Specification (DOCSIS) Remote Physical layer (R-PHY) network;

determining a time difference between a first clock at the first hardware device and a second clock at the second hardware device from the time synchronization message;

re-stamping an event message based on the time difference;

receiving, at the first hardware device, a Media Access Protocol (MAP) message from the second hardware device;

identifying a stitch point in the MAP message; and

modifying the MAP message at the stitch point based on the time difference, wherein the modifying comprises adding a MAP timing unit at the stitch point if the clock drift indicates that an under-run threshold is crossed.

2. The method of claim 1, wherein the first hardware device comprises a Converged Cable Access Platform (CCAP) core and the second hardware device comprises a Remote Physical Layer interface (R-PHY) node, wherein the CCAP core and the R-PHY node together comprise a portion of a Cable Modem Transmission System (CMTS).

3. The method of claim 1, wherein re-stamping comprises adjusting a timestamp on the event message to match a remote time of the second clock.

4. The method of claim 1, further comprising:

inserting time at a logical clock at the first hardware device if the first clock is slower than the second clock; and

deleting time at the logical clock if the first clock is faster than the second clock.

5. The method of claim 1, further comprising:

hastening downstream transmissions from the first hardware device if the first clock is slower than the second clock; and

delaying downstream transmissions from the first hardware device if the first clock is faster than the second clock.

6. The method of claim 1, further comprising determining a frequency difference between the first clock and the second clock.

7. The method of claim 1, further comprising:

adding samples in narrowband digital forward transmissions from the first hardware device if the first clock is slower than the second clock; and

puncturing samples in narrowband digital forward transmissions from the first hardware device if the first clock is faster than the second clock.

8. The method of claim 7, wherein rates of puncturing of samples and addition of samples are based on the time difference.

9. The method of claim 1, further comprising:

receiving, at the first hardware device, a plurality of time synchronization messages from a plurality of remote second hardware devices in the network;

determining respective time differences between the first clock at the first hardware device and a plurality of second clocks at each of the plurality of second hardware devices from the plurality of time synchronization messages, the plurality of second clocks comprising separate clock domains; and

re-stamping a plurality of event messages based on the time differences.

10. The method of claim 9, wherein the first hardware device generates separate local clock domain islands corresponding to the separate clock domains, wherein each local clock domain island tracks the respective time difference of the corresponding separate clock domain with the local time at the first clock.

11. The method of claim 10, wherein the separate local clock domain islands hasten downstream transmissions from the first hardware device in the corresponding clock domain if the first clock is slower than the second clock associated with the corresponding clock domain, and wherein the separate local clock domain islands delay downstream transmissions from the first hardware device in the corresponding clock domain if the first clock is faster than the second clock associated with the corresponding clock domain.

12. The method of claim 1, wherein determining the time difference comprises computing network delay and clock drift from a rolling sample table.

13. The method of claim 1, wherein the first hardware device comprises a R-PHY node and the second hardware device comprises a CCAP core, wherein the CCAP core and the R-PHY node together comprise a portion of a CMTS.

14. The method of claim 1, wherein re-stamping comprises adjusting a timestamp on the event message to match a local time of the first clock.

15. The method of claim 1, wherein the modifying the MAP message comprises deleting a MAP timing unit at the stitch point if the clock drift indicates that an overrun threshold is crossed.

16. The method of claim 1, wherein the MAP message comprises a short MAP message including a timing unit that can be deleted.

17. The method of claim 1, wherein the MAP message comprises a regular MAP message including a null entry that can be added to.

18. The method of claim 1, wherein the MAP message includes a plurality of stitch points corresponding to the time difference.

19. Non-transitory tangible computer readable media that includes instructions for execution, which when executed by a processor, performs operations comprising:

receiving, at a first hardware device, a time synchronization message from a remote second hardware device in a DOCSIS R-PHY network;

determining a time difference between a first clock at the first hardware device and a second clock at the second hardware device from the time synchronization message;

re-stamping an event message based on the time difference;

receiving, at the first hardware device, a MAP message from the second hardware device;

identifying a stitch point in the MAP message; and

modifying the MAP message at the stitch point based on the time difference, wherein the modifying comprises adding a MAP timing unit at the stitch point if the clock drift indicates that an under-run threshold is crossed.

20. The media of claim 19, wherein re-stamping comprises adjusting a timestamp on the event message to match a remote time of the second clock.

21. The media of claim 19, wherein the operations further comprise:

hastening downstream transmissions from the first hardware device if the first clock is slower than the second clock; and

delaying downstream transmissions from the first hardware device if the first clock is faster than the second clock.

22. The media of claim 19, wherein the operations further comprise:

adding samples in narrowband digital forward transmissions from the first hardware device if the first clock is slower than the second clock; and

puncturing samples in narrowband digital forward transmissions from the first hardware device if the first clock is faster than the second clock.

23. The media of claim 22, wherein rates of puncturing of samples and addition of samples are based on the time difference.

24. The media of claim 19, wherein the modifying the MAP message comprises deleting a MAP timing unit at the stitch point if the clock drift indicates that an overrun threshold is crossed.

25. The media of claim 19, wherein the MAP message includes a plurality of stitch points corresponding to the time difference.

26. An apparatus, comprising:

a first hardware device including a first clock;

a memory element for storing data; and

a processor, wherein the processor executes instructions associated with the data, wherein the processor and the memory element cooperate, such that the apparatus is configured for;

receiving, at the first hardware device, a time synchronization message from a remote second hardware device in a DOCSIS R-PHY network;

determining a time difference between the first clock at the first hardware device and a second clock at the second hardware device from the time synchronization message;

re-stamping an event message based on the time difference;

receiving, at the first hardware device, a MAP message from the second hardware device;

identifying a stitch point in the MAP message; and

modifying the MAP message at the stitch point based on the time difference, wherein the modifying comprises adding a MAP timing unit at the stitch point if the clock drift indicates that an under-run threshold is crossed.

27. The apparatus of claim 26, wherein re-stamping comprises adjusting a timestamp on the event message to match a remote time of the second clock.

28. The apparatus of claim 26, further configured for:

hastening downstream transmissions from the first hardware device if the first clock is slower than the second clock; and

delaying downstream transmissions from the first hardware device if the first clock is faster than the second clock.

29. The apparatus of claim 26, further configured for:

adding samples in narrowband digital forward transmissions from the first hardware device if the first clock is slower than the second clock; and

puncturing samples in narrowband digital forward transmissions from the first hardware device if the first clock is faster than the second clock.

30. The apparatus of claim 29, wherein rates of puncturing of samples and addition of samples are based on the time difference.

31. The apparatus of claim 26, wherein the modifying the MAP message comprises deleting a MAP timing unit at the stitch point if the clock drift indicates that an overrun threshold is crossed.

32. The apparatus of claim 26, wherein the MAP message includes a plurality of stitch points corresponding to the time difference.