PON Time Synchronization via Asymmetric Delay Compensation
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Solution Overview
Problem
In passive optical networks (PONs), existing time synchronization methods using Precision Time Protocol (PTP) assume equal delays from the master clock (MC) to the slave clock (SC) and back, leading to inaccurate synchronization due to potential differences in these delays, resulting in asynchronous clocks.
Innovation Solution
A method and device that involve sending a synchronization packet from the optical line terminal (OLT) with a timestamp after achieving time synchronization with the MC, allowing the optical network units (ONUs) to adjust their local clocks and instruct the SC to perform synchronization, thereby accounting for different delays and ensuring accurate time synchronization between MC and SC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the PTP protocol assumes equal delays for forward and reverse paths, then the synchronization process is simplified, but the time synchronization accuracy deteriorates due to actual delay differences
Solution Approach 1:
The patent implements a feedback mechanism where the slave clock measures the actual forward delay (T1 to T2) and communicates this information back to the master clock. The master clock then uses this feedback to calculate and compensate for the delay difference, adjusting its timestamp to account for the asymmetric delay. This feedback loop enables accurate time synchronization without requiring the simplifying assumption of equal forward and reverse delays.
2Ease of operation
If the delay difference between MC to SC and SC to MC is not compensated, then the synchronization method remains simple, but the time synchronization reliability deteriorates resulting in asynchronous clocks
Solution Approach 1:
The patent changes the parameter being synchronized from assuming equal delays to actually measuring and compensating for delay differences. Specifically, it measures the forward delay parameter (T1 to T2) and uses this measured value to adjust the synchronization calculation, rather than relying on the theoretical assumption of equal delays. This parameter change from assumption to measurement-based compensation improves reliability while maintaining operational simplicity.
Data Source
AI summary
A time synchronization method and a time synchronization device in a passive optical network (PON), and a PON are provided. The method includes receiving a synchronization packet sent after time synchronization of an optical line terminal (OLT) with a master clock (MC) is achieved, wherein the synchronization packet carries a timestamp TMt1i determined after the time synchronization of the OLT is achieved, adjusting a local clock according to the timestamp to achieve time synchronization of an optical network unit/optical network terminal (ONU/ONT) with the OLT, and after the time synchronization of the OLT is achieved, instructing an slave clock (SC) to perform time synchronization. A time synchronization device and a time synchronization system for implementing the method in a PON are further provided.