Transparent Clock Skew Estimation Using PTP Timestamps
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Solution Overview
Problem
Current methods for estimating clock skew in end-to-end transparent clocks, such as those used in IEEE 1588 PTP networks, are inaccurate due to simplistic syntonization techniques and require physical synchronization or hardware timestamping, which are not applicable to all network deployments.
Innovation Solution
A method and system for estimating clock skew in end-to-end transparent clocks using timing messages exchanged between a master and slave device, allowing for accurate syntonization without physical synchronization, by extracting and processing timestamps to calculate the skew of a local clock relative to a master clock, using techniques like linear approximation or Kalman filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Synchronous Ethernet (SyncE) is used to syntonize TC clocks to the GrandMaster, then clock skew is reduced and residence time measurements are improved, but the network requires all SyncE infrastructure which increases device complexity and deployment difficulty
Solution Approach 1:
The patent uses PTP timing messages as an intermediary carrier to transmit skew estimation information between the GrandMaster and Transparent Clocks. Instead of requiring direct physical synchronization infrastructure like SyncE, the system embeds timestamp data in PTP messages that pass through the network, allowing skew estimation without dedicated timing infrastructure.
Solution Approach 2:
The patent replaces the mechanical/physical synchronization system (SyncE hardware infrastructure) with a software-based processing approach. By using processor-based timestamp extraction and skew estimation algorithms, the system achieves syntonization functionality without requiring physical layer timing infrastructure.
2Measurement precision
If physical syntonization is implemented to achieve accurate clock synchronization, then clock skew is minimized, but hardware timestamping and physical synchronization infrastructure are required which limits applicability
Solution Approach 1:
The patent substitutes physical hardware timestamping mechanisms with software-based timestamp extraction from PTP message headers. This allows skew estimation to be implemented in standard network equipment without specialized hardware, greatly improving adaptability to existing network deployments.
Solution Approach 2:
The patent makes the Transparent Clock functionality universal by using standard PTP messages that can be processed by any equipment supporting IEEE 1588. The same mechanism works whether or not SyncE is present, making the solution applicable to diverse network configurations without requiring specialized hardware.
3Ease of manufacture
If simple linear estimation is used to generate syntonization signals from Sync messages, then implementation is straightforward, but syntonization accuracy is insufficient for precise residence time measurements
Solution Approach 1:
The patent implements a feedback mechanism where the Transparent Clock continuously monitors the relationship between its local clock and the GrandMaster clock using timestamps from bidirectional PTP messages. This feedback loop enables dynamic skew estimation and compensation, improving accuracy over static linear estimation methods.
Solution Approach 2:
The patent transitions from static linear estimation to dynamic skew estimation by continuously updating the skew calculation based on recent timestamp measurements. The system adapts to changing network conditions and clock drift by processing ongoing message exchanges, improving syntonization accuracy while maintaining practical implementation complexity.
Data Source
AI summary
This invention relates to end-to-end transparent clocks and methods of estimating skew in end-to-end transparent clocks. Embodiments of the invention relate to techniques for estimating clock skew between a free-running clock in a transparent clock and a master clock, in particular by using the timing information embedded in timing messages passing through the transparent clock. Further embodiments of the invention set out uses of these estimates to modify the residence times computed by the transparent clock and a synchronization network including such transparent clocks.