Precision time protocol using a coherent optical DSP frame

1. A coherent optical modem in a first node, the coherent optical modem comprising:

an optical interface; and

circuitry connected to the optical interface and configured to

detect a first timing reference point in a transmit Digital Signal Processor (DSP) frame in a transmit direction from the first node to a second node, and

detect a second timing reference point in a receive DSP frame in a receive direction from the second node to the first node,

wherein the second timing reference point is determined based on a pattern in the received DSP frame that includes multiple bits that are processed prior to Forward Error Correction (FEC), in any DSP frame field including i) a padding area, ii) a reserved area, and iii) a DSP Multi-Frame Alignment Signal (MFAS) area.

2. The coherent optical modem of claim 1 , wherein a time difference between the first node and the second node is determined based in part on the first timing reference point and the second timing reference point and corresponding timing reference points from the second node.

3. The coherent optical modem of claim 1 , wherein the pattern is input in select DSP frames for a time period between timing reference points that is greater than a time period for each DSP frame.

4. The coherent optical modem of claim 1 , wherein the pattern includes a fixed value.

5. The coherent optical modem of claim 1 , wherein the pattern includes a Pseudorandom Binary Sequence (PRBS).

6. The coherent optical modem of claim 1 , wherein timing information from the second node is provided to the first node via a synchronization messaging channel.

7. The coherent optical modem of claim 1 , wherein the coherent optical modem utilizes a Flexible Optical Transport Network (FlexO) or an Open Reconfigurable Optical Add/Drop Multiplexer (OpenROADM) interface.

8. The coherent optical modem of claim 1 , wherein the coherent optical modem utilizes a ZR, as defined in the Optical Internetworking Forum (OIF) Implementation Agreement 400ZR, OIF-400ZR-01.0, Mar. 10, 2020, or an OpenZR+ interface, as defined in OpenZR+ Specification, version 1.0, Sep. 4, 2020.

9. The coherent optical modem of claim 1 , wherein the DSP frame is compliant to G.709.3 Amendment 1 or Optical Internetworking Forum (OIF) Implementation Agreement 400ZR.

10. A method implemented in a first node including a coherent optical modem in communication with a corresponding coherent optical modem in a second node, the method comprising:

receiving a departure time, T D-A , from the second node, wherein the departure time, T D-A , is determined by the second node based on detecting a timing reference point in a Digital Signal Processor (DSP) frame;

determining an arrival time, T A-B , based on detecting the timing reference point in the DSP frame that includes a pattern of multiple bits in any DSP frame field processed prior to Forward Error Correction (FEC); and

determining a time difference between the first node and the second node based in part on the departure time, T D-A , and the arrival time, T A-B .

11. The method of claim 10 , wherein the any DSP frame field includes any of i) a padding area, ii) a reserved area, and iii) a DSP Multi-Frame Alignment Signal (MFAS) area.

12. The method of claim 11 , wherein the pattern is input in select DSP frames for a time period between timing reference points that is greater than a time period for each DSP frame.

13. The method of claim 11 , wherein the pattern includes a fixed value.

14. The method of claim 11 , wherein the pattern includes a Pseudorandom Binary Sequence (PRBS).

15. The method of claim 10 , wherein timing information from the second node is provided to the first node via a synchronization messaging channel.

16. The method of claim 10 , wherein the coherent optical modem utilizes a Flexible Optical Transport Network (FlexO) or an Open Reconfigurable Optical Add/Drop Multiplexer (OpenROADM) interface.

17. The method of claim 10 , wherein the coherent optical modem utilizes a ZR, as defined in the Optical Internetworking Forum (OIF) Implementation Agreement 400ZR, OIF-400ZR-01.0, Mar. 10, 2020, or an OpenZR+ interface, as defined in OpenZR+ Specification, version 1.0, Sep. 4, 2020.

18. The method of claim 10 , wherein the DSP frame is compliant to G.709.3 Amendment 1 or Optical Internetworking Forum (OIF) Implementation Agreement 400ZR.