Optical Ethernet Clock Synchronization for Low-Jitter TDM Transport
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Solution Overview
Problem
Conventional Ethernet networks lack a mechanism for providing clock synchronization and distribution, making it difficult to support TDM traffic streams and resulting in high jitter and wander, which do not meet common carrier telecommunication standards, especially when transferring legacy TDM traffic over asynchronous networks.
Innovation Solution
A clock synchronization mechanism that extracts and adapts disparate clock rates from optical Ethernet signals to a common rate, selects a primary clock, and generates synchronized Ethernet output clocks, effectively turning an asynchronous Ethernet network into a synchronous one, suitable for distributing synchronous TDM data streams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional asynchronous Ethernet networks are used to transfer TDM traffic, then network scalability and cost are improved, but clock synchronization quality deteriorates resulting in high jitter and wander
Solution Approach 1:
The patent introduces a clock synchronization intermediary device that extracts clocks from received Ethernet packets, adapts them to a common rate, selects the best clock source, and regenerates synchronized clock signals. This intermediary mechanism enables asynchronous Ethernet networks to carry synchronous TDM traffic by mediating between the asynchronous network transport and the synchronous TDM requirements, thereby resolving the contradiction between network scalability and clock synchronization quality.
2Reliability
If SONET/SDH synchronous networks are used for clock distribution, then clock synchronization quality is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the complex SONET/SDH mechanical synchronous network infrastructure with an Ethernet-based system that uses packetized clock transport and software-controlled clock adaptation. Instead of requiring dedicated synchronous physical layers and complex SONET equipment, the invention uses standard Ethernet packets carrying clock information, processed by programmable clock adaptation logic, thereby achieving comparable synchronization quality with significantly reduced device complexity.
3Adaptability or versatility
If multiple disparate clock rates are extracted from optical Ethernet signals, then adaptability to different Ethernet speeds is improved, but clock rate variation increases making synchronization difficult
Solution Approach 1:
The patent employs parameter change by extracting clock rates from Ethernet signals at different speeds (100Mbps, 1Gbps, 10Gbps) and systematically adapting them to a unified common clock rate through programmable division and synchronization. The system dynamically adjusts the clock adaptation parameters based on the input Ethernet speed, converting variable clock rates into consistent synchronized output clocks, thereby resolving the contradiction between Ethernet speed adaptability and clock rate consistency.
Data Source
AI summary
A novel clock synchronization mechanism for recovering and distributing a centralized clock source synchronously over asynchronous networks such as optical Ethernet. A clock conversion scheme is provided whereby multiple clocks having diverse rates are converted to clock signals all having a common rate. One of the converted clocks is chosen and all downstream clock signals is derived from this clock. A high quality clock source located anywhere on the network is distributed throughout the network thus turning an asynchronous Ethernet network into a synchronous one. Synchronous TDM data streams can then be easily transported over the Ethernet network.