PON Time Transfer Using PPnS Timestamps and Ranging
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Solution Overview
Problem
The Precision Time Protocol (PTP) experiences complicated processing and excessive network bandwidth occupancy in passive optical networks (PON) due to asymmetric delay characteristics, leading to inefficiencies in time synchronization.
Innovation Solution
A method and system for time transfer in PON that involves an optical line terminal (OLT) generating periodic pulse per n second (PPnS) timestamps and time of day (TOD) based on a local reference counter, with OLTs ranging optical network units (ONUs) and transmitting this information, allowing ONUs to predict the next second's PPnS and maintain accurate time synchronization with low bandwidth usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PTP protocol is used in PON for time synchronization, then time transfer capability is achieved, but processing complexity and network bandwidth occupancy increase excessively
Solution Approach 1:
The patent extracts the time synchronization function from the complex PTP protocol stack and implements it directly at the physical layer through dedicated timestamp fields in PON frames. This separates the time transfer function from the data plane processing, eliminating the need for complex PTP protocol handling while maintaining synchronization accuracy.
Solution Approach 2:
The patent integrates time synchronization functionality into the existing PON infrastructure by utilizing standard PON frame structures and existing OLT-ONU communication mechanisms. The same PON infrastructure that handles data traffic also carries precise timing information through embedded timestamps, making the system multi-functional without adding separate complex protocol layers.
2Reliability
If PTP protocol is used in PON for time synchronization, then time transfer capability is achieved, but network bandwidth occupancy increases excessively
Solution Approach 1:
The patent merges the time synchronization function with the existing PON data traffic by embedding timestamps within standard PON frame structures. Instead of using separate dedicated bandwidth for timing protocols, the timing information is combined with data planes, utilizing existing bandwidth efficiently without requiring additional network resources.
3Reliability
If PTP protocol is used in asymmetric PON network, then time transfer is possible, but excessive protocol workload occurs
Solution Approach 1:
The patent replaces the complex software-based PTP protocol processing with simplified hardware-level timestamp insertion and extraction mechanisms. The OLT and ONU use dedicated hardware counters and timestamp fields that automatically capture and transfer timing information without requiring software protocol interpretation, dramatically reducing processing workload.
Data Source
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AI summary
The present invention discloses a method and system for accurate time transfer in PON, used to solve the technical problems of the processing procedure being complicated, the protocol workload being huge and excessive network bandwidth being occupied when using the Precision Time Protocol in network to transfer time in PON. In the present invention, an Optical Line Terminal (OLT) ranges Optical Network Units (ONUs) and obtains ranging information, then, triggered by the periodic Pulse per n Second (PPnS), generates a PPnS timestamp based on the local reference counter and the Time of Day (TOD) above second; OLT transmits the ranging information, the periodic PPnS timestamp and TOD to ONUs; ONUs predicts the time of the next second according to said periodic PPnS timestamp, TOD and ranging information, and outputs the corresponding PPnS. The invention is characterized by the combination of the features of PON point to multi-point and PON ranging into its time transfer method, the high accuracy of time transfer, and the low hardware costs for OLT and ONU, as well as the extremely small bandwidth occupancy due to the usage of a single copy of PON itself to broadcast the time information.