Peer-to-Peer Transparent Clocks for PTP Synchronization
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Solution Overview
Problem
IEEE 1588 PTP-based time synchronization in networks faces challenges due to timing impairments like packet delay variation (PDV) and delay asymmetry, which affect the accuracy of clock synchronization in slave devices, as these issues cannot be fully mitigated by existing Boundary Clocks (BCs) and Transparent Clocks (TCs).
Innovation Solution
The method involves using peer-to-peer transparent clocks to estimate and communicate residence times and propagation delays, allowing slave devices to accurately adjust their clocks and compensate for delay variations by incorporating these measurements into the correction field of timing messages, 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 time distribution accuracy is improved, but packet delay variation and delay asymmetry still affect synchronization precision
Solution Approach 1:
The patent segments the timing measurement process by having each Transparent Clock independently measure and record its own residence time for passing PTP messages. Instead of relying on a single end-to-end measurement, the total delay is segmented into multiple per-hop measurements that are summed along the path, allowing more precise tracking of timing impairments at each network element.
Solution Approach 2:
The patent implements feedback by having Transparent Clocks communicate their measured residence times back to the slave device through the correction field of PTP messages. This feedback mechanism allows the slave to compensate for measured delays and variations, improving synchronization precision by using actual observed timing data from each network element.
2Measurement precision
If peer-to-peer transparent clocks estimate and communicate residence times and propagation delays, then synchronization accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes Transparent Clocks multi-functional by combining their existing residence time measurement capability with peer delay estimation functionality. The same hardware and software infrastructure used for timestamping and residence time measurement is leveraged to also estimate propagation delays, eliminating the need for separate dedicated measurement devices and reducing overall system complexity.
Solution Approach 2:
The Transparent Clocks perform self-measurement of their residence times and self-estimation of propagation delays using their own internal clocks and timing mechanisms. Each device independently generates and processes the measurement data without requiring external measurement equipment, reducing system complexity while maintaining high measurement precision.
Data Source
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.