Compensating Path Asymmetry in IEEE 1588 PTP Synchronization
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Solution Overview
Problem
Existing methods for clock synchronization in packet networks, such as those using IEEE 1588 PTP, face challenges in compensating for path asymmetry due to unequal queuing delays and physical link differences, leading to significant time errors that can accumulate and exceed tolerance limits, especially in mobile networks.
Innovation Solution
A method and system that estimate asymmetric delays by calculating forward and reverse displacement factors from timestamps of timing messages exchanged between master and slave devices, allowing for compensation of queue-induced asymmetries without relying on network timing support mechanisms like boundary clocks or transparent clocks, and enabling transparency across different network types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If end-to-end timing transfer is used without network timing support mechanisms, then device complexity is reduced and transparency across network types is achieved, but time synchronization precision deteriorates due to uncorrected queuing delays and path asymmetry
Solution Approach 1:
The system performs self-calibration by automatically measuring and compensating for path asymmetry using timestamped message exchanges between master and slave devices. The slave device calculates forward and reverse path delays, determines the asymmetry, and applies compensation to achieve accurate time synchronization without requiring external calibration or complex network infrastructure
Solution Approach 2:
The system uses bidirectional timestamped message exchanges to measure path delays in both directions. The slave device receives timestamps from the master, sends response messages with its own timestamps, and uses the round-trip timing information to calculate and compensate for path asymmetry, creating a closed-loop feedback mechanism for continuous synchronization refinement
2Measurement precision
If boundary clocks and transparent clocks are deployed to eliminate delay asymmetry, then time synchronization accuracy is improved, but device complexity increases and network transparency is reduced due to node-by-node implementation requirements
Solution Approach 1:
The invention extracts the path asymmetry measurement and compensation functions from intermediate network nodes (boundary clocks and transparent clocks) and relocates them to the end devices (master and slave). This eliminates the need for complex node-by-node timing support mechanisms while achieving the same asymmetry compensation goal through end-to-end measurement and correction
3Measurement precision
If manual calibration of fiber links and internal timing paths is performed, then time synchronization precision is improved by correcting physical link asymmetry, but ease of operation deteriorates due to manual intervention requirements
Solution Approach 1:
The system performs automatic self-calibration by measuring path asymmetry through timestamped message exchanges and applying compensation algorithms without requiring manual intervention. The slave device automatically calculates forward and reverse path delays, determines asymmetry, and adjusts its time synchronization accordingly, eliminating the need for manual fiber link calibration while maintaining high precision
Data Source
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AI summary
This invention relates to methods and devices for compensating for path asymmetry, particularly with reference to time and frequency synchronization. The invention has particular application where time and frequency synchronization over packet networks using, for example, the IEEE 1588 Precision Time Protocol (PTP) is being carried out. Typically communication path delays between a time server (master) and a client (slave) are estimated using the assumption that the forward delay on the path is the same as the reverse delay. As a result, differences between these delays (delay asymmetries) can cause errors in the estimation of the offset of the slave clock from that of the master. Embodiments of the invention provide techniques and devices for compensating for path delay asymmetries that arise when timing protocol messages experience dissimilar queuing delays in the forward and reverse paths.