Compensating Path Asymmetry in IEEE 1588 PTP Synchronization
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Solution Overview
Problem
Existing methods for clock synchronization using IEEE 1588 PTP struggle with compensating for path asymmetry due to unequal queuing delays and physical link differences, leading to significant time errors, especially in packet networks where network timing support mechanisms like boundary clocks and transparent clocks are insufficient.
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, and enabling accurate synchronization across different network types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If end-to-end timing transfer without network timing support mechanisms is used, then device complexity is reduced and transparency across network types is achieved, but time synchronization precision deteriorates due to uncorrected queuing delays
Solution Approach 1:
The patent implements feedback by measuring the actual queuing delay experienced by timing messages using displacement factors, then using this measured information to compensate for the delay asymmetry. The slave device calculates forward displacement factors from multiple timing messages and feeds this delay information back to correct the time synchronization, achieving both simplicity and precision.
2Measurement precision
If boundary clocks and transparent clocks are deployed to eliminate queuing delay asymmetry, then time synchronization precision is improved, but device complexity and network infrastructure requirements increase
Solution Approach 1:
The patent applies self-service by enabling the end devices (master and slave) to independently measure and compensate for their own queuing delays without requiring special network infrastructure. The slave device autonomously calculates forward and reverse displacement factors from exchanged timing messages and performs self-correction, eliminating the need for boundary clocks or transparent clocks.
3Measurement precision
If manual calibration of physical links is performed to correct fiber length asymmetry, then time synchronization precision is improved, but ease of operation deteriorates due to manual intervention requirements
Solution Approach 1:
The patent changes the approach from static physical calibration to dynamic parameter measurement and adjustment. Instead of manually fixing physical link asymmetries, the system dynamically measures the actual timing displacement caused by various asymmetries (queuing, physical links, internal processing) and adjusts the time synchronization parameters accordingly, achieving automatic compensation that adapts to changing network conditions.
Data Source
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.