Asymmetry Correction for Precise Clock Synchronization Over Optical Fiber
AssigneeSymmetricom, Inc.
InventorSanjay Mani
Life of this patent
Estimating the term…
Abstract
A clock at a first network element that is connected to a second network element over an optical fiber link is aligned in time/phase using packet protocols such as PTP. The invention discloses how to correct the asymmetry error inherent in traditional packet-based time-transfer methods.
Claims20
In an optical network including a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other, a method for estimating an asymmetry of transit delay in the first and second optical links, the method comprising:
- aligning a first clock at the first network element and a second clock at the second network element to a nominal frequency;
- measuring a first phase shift at the second clock when the first clock is operated at a frequency greater than the nominal frequency;
- measuring a second phase shift at the second clock when the first clock is operated at a frequency less than the nominal frequency;
- and
- estimating the asymmetry of transit delay in the first and second optical links based on the first and second phase shifts.
In an optical network including a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other, a method for estimating a path length of the first optical link, the method comprising:
- aligning a first clock at the first network element and a second clock at the second network element to a nominal frequency;
- measuring a first phase shift at the second clock when the first clock is operated at a frequency greater than the nominal frequency;
- measuring a second phase shift at the second clock when the first clock is operated at a frequency less than the nominal frequency;
- and
- estimating the path length of the first optical link based on the first and second phase shifts.
In an optical network including a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other, a method for estimating an asymmetry of transit delay in the first and second optical links, the method comprising:
- aligning a first clock at the first network element and a second clock at the second network element to a nominal frequency;
- measuring a first phase difference between a transmitted and a received wave at the first network element, wherein the first phase difference is measured with reference to a local time at the first network element;
- measuring a second phase difference between a transmitted and a received wave at the second network element, wherein the second phase difference is measured with reference to a local time at the second network element;
- and
- estimating the asymmetry of transit delay in the first and second optical links based on the first and second phase differences.
In an optical network including a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other, a method for estimating a path length of the first optical link, the method comprising:
- aligning a first clock at the first network element and a second clock at the second network element to a nominal frequency;
- measuring a first phase difference between a transmitted and a received wave at the first network element, wherein the first phase difference is measured with reference to a local time at the first network element;
- measuring a second phase difference between a transmitted and a received wave at the second network element, wherein the second phase difference is measured with reference to a local time at the second network element;
- and
- estimating the path length of the first optical link based on the first and second phase differences.
Dependencies are inferred from the claim text.