Hitless Protection in High-Speed OTN Framers via Parallel FAS Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-speed optical transport networks, achieving hitless protection by switching from a primary to a backup line card without causing signal loss or synchronization issues is challenging due to the difficulty in aligning bit and phase signals, especially at high data rates like 100 Gb/s with QPSK modulation and polarization mode multiplexing, where bit periods are very short.
Innovation Solution
The method employs multiple Frame Alignment Signal (FAS) detecting modules that work in parallel, allowing the receiver to switch to a pseudo-sync state when the primary module loses synchronization, using an alternative module's detected FAS to decode frames and adjust the starting point, and only requiring phase alignment, thus eliminating the need for exact bit alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single FAS detecting module is used, then the system is simple, but the receiver loses synchronization during switching causing long recovery time
Solution Approach 1:
The single FAS detecting module is segmented into multiple parallel modules (first FAS detecting module and second FAS detecting module). Each module independently detects frame alignment signals, allowing the system to switch between them during line card transitions without losing synchronization, thus resolving the contradiction between reliability and complexity.
Solution Approach 2:
The second FAS detecting module is activated in advance and works in parallel with the first module before switching is needed. This preliminary preparation ensures that when a line card switch occurs, the standby module is already ready to detect FAS signals, eliminating synchronization loss and reducing recovery time.
2Reliability
If bit-level alignment is implemented between primary and backup interfaces, then hitless protection is achieved, but the alignment process becomes extremely difficult and time-consuming at high speeds
Solution Approach 1:
The patent extracts the bit-level alignment requirement from the system design. Instead of requiring precise bit-level alignment between primary and backup line cards, the system uses multiple parallel FAS detecting modules that can independently acquire frame synchronization. This removes the difficult alignment step while maintaining hitless protection capability.
Solution Approach 2:
The patent changes the synchronization acquisition parameter from bit-level alignment to frame-level detection. By using FAS detecting modules that search for frame alignment signals rather than requiring precise bit timing, the system achieves hitless protection without the extremely difficult and time-consuming alignment process required at high speeds like 100 Gb/s.
3Speed
If optical switching is used to switch from primary to backup line card, then switching speed is fast, but signal loss occurs during transition causing receiver desynchronization
Solution Approach 1:
The patent implements beforehand cushioning by having the second FAS detecting module ready in advance to detect frame alignment signals. When optical switching causes signal loss, the pre-positioned module can immediately acquire FAS and restore synchronization, cushioning against the desynchronization that would otherwise occur during the fast optical switching transition.
Data Source
AI summary
In an optical communication system containing a primary line and backup line card, a method includes providing interfaces for the primary and backup line card, each line card including a transmitter and receiver; and selecting output from the transmitter from either the primary or back up line card including selecting the backup line card when the primary line card encounters a failure.