PTP Clock Synchronization via RTT Delta Congestion Filtering
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Solution Overview
Problem
Existing techniques lack a deterministic mechanism to detect packet delay variations (PDVs) caused by network congestion, which hinders accurate determination of Round Trip Time (RTT) and subsequent clock synchronization in Precision Time Protocol (PTP) systems, especially in scenarios with network disruptions and clock deviations at slave devices.
Innovation Solution
The method involves determining RTT for high and low priority packet transactions between a master and slave device within a pre-defined time window, calculating average RTTs, computing an average delta RTT, and using this to determine an instantaneous network congestion level, thereby filtering out PDVs and adjusting the clock accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RTT is determined for clock synchronization in PTP protocol, then clock synchronization between master and slave devices is achieved, but network congestion causes packet delay variations that reduce the accuracy of RTT determination
Solution Approach 1:
The patent segments the RTT measurement process by separating high-priority PTP packets (_SYNC_, _DELAYREQUEST_, _DELAYRESPONSE_) from low-priority packets. By calculating RTT only for high-priority packets that are less affected by network congestion, the system achieves more accurate RTT determination despite network conditions, directly resolving the contradiction between measurement precision and reliability
Solution Approach 2:
The patent changes the parameter used for RTT calculation from general packet delay to specifically high-priority packet delay. This parameter change filters out the effects of network congestion on low-priority packets, thereby improving RTT determination accuracy while maintaining reliable clock synchronization
2Measurement precision
If network congestion detection mechanism is added to filter PDVs from RTT, then clock synchronization accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a dynamic mechanism where the system automatically adjusts its behavior based on network conditions. By dynamically identifying and filtering out PDVs caused by congestion through packet priority analysis, the system improves clock synchronization accuracy without requiring complex manual intervention or configuration, balancing accuracy improvement with acceptable device complexity
3Quantity of substance
If RTT determination includes all packet transactions, then more data is available for time adjustment, but packet delay variations due to congestion reduce the accuracy of time synchronization
Solution Approach 1:
The patent applies local quality by treating different packet priorities differently in the RTT calculation process. High-priority PTP packets are selected for RTT determination because they exhibit more consistent delay characteristics, while low-priority packets are excluded. This selective approach ensures that the data used for time adjustment has higher precision, resolving the contradiction between data quantity and precision
Data Source
AI summary
The disclosure relates to method and system for determining network congestion level. The method includes determining a round trip time (RTT) for each high priority and for each low priority packet transaction in the precision time protocol (PTP) protocol. The high priority and the low priority packet transactions are conducted between a master device and a slave device within a pre-defined time window. The method further includes determining an average high priority RTT and an average low priority RTT based on the RTT for each high priority packet transaction and for each low priority packet transaction respectively, computing an average delta RTT based on a difference between the average high priority RTT and the average low priority RTT, and determining an instantaneous network congestion level based on the average delta RTT and a reference delta RTT for a number of pre-defined time windows since a start of the slave device.