PTP Clock Skew Correction via Uplink Downlink Delay Comparison
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Solution Overview
Problem
Existing techniques for clock synchronization in communication networks, particularly using Precision Time Protocol (PTP), fail to accurately detect and correct instantaneous clock skew due to network variations, leading to inaccuracies in time adjustments at slave devices.
Innovation Solution
A method and system that determine uplink and downlink delays based on multiple packet transactions within a defined time window, calculate changes in these delays relative to reference values, and correct clock skew only when changes in both delays are of similar magnitude and opposite direction, thereby isolating network variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PTP synchronization is used to correct clock skew at slave device, then time synchronization accuracy is improved, but network variations cause packet delay variations that corrupt RTT/PD measurement
Solution Approach 1:
The patent extracts and isolates the clock deviation component from the total RTT/PD measurement by comparing uplink and downlink path delays. By taking the difference between these two measurements, the method separates clock skew from network-induced delays, allowing accurate clock correction even in varying network conditions.
Solution Approach 2:
The patent introduces an intermediary mechanism that uses multiple RTT/PD measurements (uplink and downlink) as mediators to indirectly determine clock skew. Instead of directly measuring clock deviation, the method uses path delay comparisons as an intermediary to infer the clock skew value.
2Ease of operation
If instantaneous clock deviation detection is performed using RTT/PD variations, then clock skew correction is achieved, but network congestion and disruptions cause false corrections
Solution Approach 1:
The patent implements a feedback mechanism where the slave device continuously monitors both uplink and downlink path delays, compares their variations, and adjusts clock correction decisions based on this feedback. When uplink and downlink delay variations are consistent, clock correction is applied; when they differ significantly (indicating network issues), correction is withheld.
Solution Approach 2:
The patent converts the potentially harmful effect of network variations into a beneficial diagnostic tool. By monitoring how uplink and downlink delays respond to network conditions, the method uses these variations to identify when network issues are present, thereby preventing false clock corrections while still allowing corrections when appropriate.
3Device complexity
If existing techniques detect clock skew using single-path delay variations, then detection simplicity is maintained, but detection accuracy deteriorates due to network variations
Solution Approach 1:
The patent merges multiple measurement approaches (uplink path delay and downlink path delay) into a unified clock skew detection mechanism. By combining these two complementary measurements and comparing their variations, the method achieves more accurate and reliable clock skew detection than single-path approaches while maintaining reasonable system complexity.
Data Source
AI summary
The disclosure relates to method and system for correcting a clock skew in a slave device using a precision time protocol (PTP). The method includes determining an uplink delay and a downlink delay, based on at least two packet transactions in the PTP protocol and conducted between the slave device and a master device within a pre-defined accumulator time window. The method further includes determining a change in the uplink/downlink delay with respect to a reference uplink/downlink delay. The reference uplink/downlink delay correspond to a first pre-defined accumulator time window at a start of the slave device, or to a last pre-defined accumulator time window during a previous correction of the clock skew. The method further includes correcting the clock skew upon determining the change in the uplink delay to be about same in magnitude as and to be in opposite direction to the change in the downlink delay.