Time Synchronization Asymmetry Calculation in OTN Networks
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Solution Overview
Problem
Current methods for time synchronization in communications networks, such as those using the Precision Time Protocol (PTP) over Optical Transport Networks (OTN), assume equal path delays, which leads to reduced accuracy when asymmetry occurs, and require processing PTP data at each node, complicating multi-operator network scenarios.
Innovation Solution
A method that calculates path delay asymmetry by determining forward and reverse mapping delays, FEC delays, and fibre delays, providing these values to a path delay asymmetry calculation element rather than processing PTP data at each node, allowing for simultaneous synchronization between master and slave clocks across different client networks operated by different operators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PTP data is processed at each node across the OTN network, then time synchronization can be achieved, but the complexity of the system increases and multiple operators sharing the network face difficulties
Solution Approach 1:
The patent extracts the PTP processing function from individual network nodes and consolidates it into dedicated boundary clock devices. This removes the complexity of configuring every node while maintaining synchronization accuracy, as only the boundary clocks need to handle PTP protocols.
Solution Approach 2:
The boundary clock devices serve multiple functions: they process PTP packets, manage time synchronization, and interface between OTN and client networks. This multi-functionality reduces the need for specialized configuration at each node while maintaining reliability.
2Measurement precision
If path delay asymmetry is not accounted for, then the synchronization system is simpler, but time synchronization accuracy is significantly reduced
Solution Approach 1:
The system performs preliminary measurement of forward and reverse path delays between boundary clocks before time synchronization. These pre-measured delay values are stored and used to compensate for asymmetry during synchronization, improving accuracy without adding real-time complexity.
Solution Approach 2:
The patent implements a feedback mechanism where path delay measurements are continuously monitored and used to adjust time synchronization calculations. The measured asymmetry values feed back into the synchronization algorithm to maintain precision despite network variations.
3Reliability
If each node supports IEEE 1588, then time synchronization is more accurate, but the cost and complexity of the network increases
Solution Approach 1:
The patent extracts the IEEE 1588 PTP processing requirement from all network nodes and concentrates it in boundary clock devices only. This allows standard OTN nodes to operate without complex PTP support while maintaining synchronization accuracy through the boundary clocks.
Solution Approach 2:
Boundary clocks act as intermediaries between the OTN network and client networks, handling all PTP protocol processing. This intermediary approach allows the OTN infrastructure to remain simple while achieving accurate time synchronization through the specialized boundary clock devices.
Data Source
AI summary
A method of providing a path delay asymmetry for time synchronization between a master clock at a first client node and a slave clock at a second client node. The method comprises: mapping a first time protocol signal (TPS) carrying master clock time protocol data (TPD) onto a first signal; determining a forward mapping delay (dmf); mapping a second TPS carrying slave clock TPD onto a second signal; determining a reverse mapping delay (dmr); applying FEC to the first signal, determining a forward FEC delay (dfecf); applying FEC to the second signal; determining a reverse FEC delay (dfecr); providing dmf, dmr, dfecf and dfecr to a calculation element; calculating a path delay asymmetry in dependence on dmf, dmr, dfecf and dfecr; and providing it to a time protocol client at the second client node.