Peer-to-Peer Transparent Clocks for PTP Synchronization
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Solution Overview
Problem
IEEE 1588 PTP-based time synchronization systems face challenges in achieving accurate clock synchronization due to packet delay variation (PDV) and delay asymmetry in network paths, which are not effectively mitigated by existing Boundary Clocks (BCs) and Transparent Clocks (TCs, especially static asymmetries and variable delays.
Innovation Solution
The method involves using peer-to-peer transparent clocks to estimate and communicate residence times and propagation delays, allowing slave devices to compensate for these variations through the correction field in PTP messages, and employing filters like exponentially weighted moving average or Kalman filters to accurately estimate skew and offset, thereby improving synchronization accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Boundary Clocks and Transparent Clocks are used to mitigate timing impairments, then packet delay variation is reduced, but static delay asymmetry and variable delays cannot be effectively compensated
Solution Approach 1:
The patent introduces peer delay measurement messages as an intermediary mechanism between master and slave clocks. These messages enable direct measurement of propagation delay through the network path, allowing the system to identify and compensate for static asymmetry and variable delays that traditional BC/TC mechanisms cannot handle. The peer delay information acts as a mediator that bridges the gap between timestamp data and actual delay characteristics.
Solution Approach 2:
The patent implements a feedback mechanism where peer delay measurements are continuously obtained and used to adjust skew and offset estimates. The system feeds back the measured peer delay information to the clock synchronization algorithm, which then refines its compensation calculations. This closed-loop feedback enables dynamic adaptation to changing network conditions and effective compensation of delay asymmetry.
2Ease of operation
If traditional timestamp-based synchronization is used, then clock synchronization is achieved, but network-induced delay variations cause synchronization errors
Solution Approach 1:
The patent changes the parameters used for synchronization by incorporating peer delay measurements alongside traditional timestamps. Instead of relying solely on timestamp differences, the system uses peer delay information to derive additional parameters (skew and offset) that explicitly account for network delay characteristics. This parameter enrichment transforms the synchronization approach to be resilient against delay variations.
Solution Approach 2:
The patent segments the delay compensation process into distinct components: timestamp-based delay measurement, peer delay measurement, skew estimation, and offset estimation. By separating these functions, the system can independently optimize each component and combine their results to achieve high accuracy. The segmentation allows targeted handling of different delay sources (propagation delay, queuing delay, processing delay).
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AI summary
This invention relates to methods and devices for time synchronization. The invention has particular application in the alignment of slave clocks to a master clock and in dealing with packet delay variation and dynamic asymmetries in the network links between them. In embodiments of the invention, the slave clock uses the peer link delay and residence times measured by peer-to-peer transparent clocks to compensate for clock synchronization errors that arise due to variability in message transfer delays. Embodiments provide a simple linear approximation technique and a Kalman filter-based technique for estimating offset and skew of the slave clock.