Clock Synchronization Status Message Segmentation for Loop Prevention
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Solution Overview
Problem
Packet transport networks face challenges in clock synchronization, particularly in complex scenarios where the quality grade of line clocks is not optimal, and clock loops can form due to inadequate protection methods defined in ITU-T Recommendations G.707 and G.8261/Y.1361.
Innovation Solution
The method extends Clock Synchronization Status Messages (SSMs) to include clock identification, quality grade, number of network elements passed, alarm indication, and forbidden-use indication, allowing network elements to automatically select the optimal routing clock, prevent non-optimal clocks from participating, and avoid clock loops by processing these messages as OAM messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the simple SSM definition from G.707 is used, then the implementation is straightforward, but the clock quality grade extraction is not optimal and clock loops may form in complex networking scenarios
Solution Approach 1:
The SSM is segmented into multiple distinct fields: clock identification field, clock quality grade field, number of network elements field, clock alarm indication field, and forbidden-use indication field. This segmentation allows each field to carry specific information needed for reliable clock selection and loop prevention while maintaining clear processing logic at each network element.
Solution Approach 2:
The invention adds new dimensions to the SSM by introducing the number of network elements field and forbidden-use indication field. These additional dimensions provide network elements with the capability to calculate clock path length and prevent clock loops, transforming the simple quality-grade-based selection into a multi-dimensional optimization process that considers both quality and path characteristics.
2Device complexity
If network elements select clock sources based only on quality grade, then the selection process is simple, but non-optimal routing clocks may be selected and clock loops may occur
Solution Approach 1:
The number of network elements field provides feedback information about the clock path length to each network element. Network elements use this feedback to calculate the total path length and select clock sources that minimize the number of hops, ensuring optimal routing while preventing clock loops through the forbidden-use indication field that marks clocks already used in the current path.
Solution Approach 2:
The forbidden-use indication field is set in advance by network elements to mark clock sources that have already been used in the current clock path. This preliminary action prevents other network elements from selecting the same clock source, thereby preventing clock loops before they can form, while maintaining a relatively simple selection process based on quality grade and path length.
Data Source
AI summary
A method for clock link automatic protection in packet transport networks is disclosed. The method includes that: extending the clock synchronization status message to allow said clock synchronization status message to include: a clock identification (ID), a quality grade of clock, the number of network elements that the clock has passed, a clock alarm indication, and a forbidden-use indication; each network element in the clock link processes the clock synchronization status message; and said each network element selected a clock source according to the clock synchronization status message. The method in the present invention allows the network elements to be able to automatically select the optimal routing clock, forbid non-optimal routing clocks to participate in the selection, and effectively prevent the clocks from looping.