Measuring fiber asymmetry

Patent metadata

Field	Value
Publication number	US-10986426-B1
Application number	US-202016732836-A
Country	US
Kind code	B1
Filing date	Jan 2, 2020
Priority date	Jan 2, 2020
Publication date	Apr 20, 2021
Grant date	Apr 20, 2021

Abstract

A method of obtaining a measure of asymmetry between optical fibers of a forward and reverse paths is provided in order to synchronize clocks of optical nodes connected by asymmetrical optical fiber paths. The method includes receiving, at first and second arrival times, from a first optical network device, a first optical signal transmitted on a first optical fiber and a second optical signal transmitted on a second optical fiber, calculating a first time difference between the second arrival time and the first arrival time. The method includes determining a measure of asymmetry between the first optical fiber and the second optical fiber based on the first time difference and a second time difference between a first time of transmission by the first optical network device of the first optical signal and a second time of transmission by the first optical network device of the second optical signal.

First claim

What is claimed is:

1. A method comprising:
receiving, at a first arrival time, from a first optical network device by a second optical network device, a first optical signal transmitted on a first optical fiber;
receiving, at a second arrival time, from the first optical network device by the second optical network device, a second optical signal transmitted on a second optical fiber, wherein the second optical fiber is a reverse path optical fiber configured to transmit optical signals from the second optical network device to the first optical network device;
calculating, by the second optical network device, a first time difference between the second arrival time of the second optical signal and the first arrival time of the first optical signal; and
determining, by the second optical network device, a measure of asymmetry between the first optical fiber and the second optical fiber based on the first time difference and a second time difference between a first time of transmission by the first optical network device of the first optical signal and a second time of transmission by the first optical network device of the second optical signal.

2. The method of claim 1 , further comprising:
receiving, by the second optical network device from the first optical network device, the second time difference computed by the first optical network device.

3. The method of claim 2 , wherein determining the measure of asymmetry between the first optical fiber and the second optical fiber includes:
calculating, by the second optical network device, a path difference based on a difference between the first time difference and the second time difference, wherein the path difference represents the measure of asymmetry.

4. The method of claim 1 , wherein receiving the second optical signal includes:
switching, by the second optical network device, from transmitting to the first optical network device, on the second optical fiber, to receiving, via the second optical fiber, the second optical signal from the first optical network device.

5. The method of claim 1 , further comprising:
frequency synchronizing a first clock of the first optical network device with a second clock of the second optical network device prior to the first optical network device transmitting the first optical signal and the second optical signal.

6. The method of claim 1 , further comprising:
converting, by the second optical network device, the measure of asymmetry into a time offset value; and
adjusting, by the second optical network device, a time reference of the second optical network device based on the time offset value.

7. The method of claim 6 , wherein adjusting the time reference includes:
adjusting an offset value based on the measure of asymmetry when computing a round trip delay based on a timing protocol between the first optical fiber and the second optical fiber.

8. The method of claim 7 , further comprising:
synchronizing a second clock of the second optical network device with a first clock of the first optical network device using the timing protocol and the offset value.

9. The method of claim 1 , wherein:
receiving the first optical signal includes receiving, by the second optical network device, the first optical signal, transmitted via an optical service channel on the first optical fiber; and
receiving the second optical signal includes receiving, by the second optical network device, the second optical signal, transmitted via the optical service channel on the second optical fiber.

10. The method of claim 1 , wherein:
receiving the first optical signal includes receiving, by the second optical network device, the first optical signal, transmitted at a first wavelength that transmits traffic data; and
receiving the second optical signal includes receiving, by the second optical network device, the second optical signal, transmitted at the first wavelength that transmits the traffic data from the second optical network device to the first optical network device.

11. The method of claim 1 , wherein:
receiving the first optical signal includes receiving, by the second optical network device, the first optical signal, transmitted over a data channel that transmits data traffic from the first optical network device to the second optical network device; and
receiving the second optical signal includes receiving, by the second optical network device, the second optical signal, transmitted over the data channel that transmits the data traffic from the second optical network device to the first optical network device.

12. The method of claim 1 , wherein the first optical signal includes a first message that contains the first time of transmission and the second optical signal includes a second message that contains the second time of transmission.

13. An apparatus comprising:
a communication interface;
a memory configured to store executable instructions; and
a processor coupled to the communication interface and the memory and configured to perform operations including:
receiving, via the communication interface, at a first arrival time, from a first optical network device, a first optical signal transmitted on a first optical fiber;
receiving, via the communication interface, at a second arrival time, from the first optical network device, a second optical signal transmitted on a second optical fiber, wherein the second optical fiber is a reverse path optical fiber configured to transmit optical signals to the first optical network device;
calculating a first time difference between the second arrival time of the second optical signal and the first arrival time of the first optical signal; and
determining a measure of asymmetry between the first optical fiber and the second optical fiber based on the first time difference and a second time difference between a first time of transmission by the first optical network device of the first optical signal and a second time of transmission by the first optical network device of the second optical signal.

14. The apparatus of claim 13 , wherein the processor is further configured to perform the operations including:
receiving, via the communication interface from the first optical network device, the second time difference computed by the first optical network device.

15. The apparatus of claim 14 , wherein the processor is configured to perform the operation of determining the measure of asymmetry between the first optical fiber and the second optical fiber by:
calculating a path difference based on a difference between the first time difference and the second time difference, wherein the path difference represents the measure of asymmetry.

16. The apparatus of claim 13 , further comprising:
a switch that switches from transmitting to the first optical network device, on the second optical fiber, to receiving, via the second optical fiber, the second optical signal from the first optical network device.

17. The apparatus of claim 13 , wherein the processor is further configured to perform the operations including:
frequency synchronizing a first clock of the first optical network device with a second clock of the apparatus prior to the first optical network device transmitting the first optical signal and the second optical signal.

18. One or more non-transitory computer readable storage media encoded with instructions that, when executed by a processor, cause the processor to perform operations including:
receiving, at a first arrival time, from a first optical network device, a first opti

Assignees

• Cisco Tech Inc

Inventors

• Loprieno Gilberto
• Chiesa Luca Della
• Binetti Stefano
• Piciaccia Stefano
• Osnago Giovanni

Classifications

• H04B10/0771

  Fault location on the transmission path · CPC title

• H04J3/0667 Primary

  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 title

• H04L7/00

  Arrangements for synchronising receiver with transmitter {(synchronisation of generators of electric oscillations or pulses H03L7/00)} · CPC title

• H04Q11/0066 Primary

  Provisions for optical burst or packet networks · CPC title

• H04B10/071

  using a reflected signal, e.g. using optical time domain reflectometers [OTDR] · CPC title