Wavelength Retuning Minimization in Colorless Directionless Optical Networks
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Solution Overview
Problem
In Colorless and Directionless (CD) architecture networks with a control plane, wavelength retuning during service redials is inefficient, leading to 'retune domino effects' and non-converging loops, which increases downtime and disrupts other services.
Innovation Solution
A method that detects link failures and sends release messages with protect paths and wavelengths to minimize wavelength retuning, using existing wavelengths first and caching protect paths, with new wavelengths determined by cyclic or recursive tree algorithms to avoid contention and loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wavelength retune is performed during service redial, then the service can be restored with a new wavelength, but additional time (30 s or more) is consumed and other services may be affected by retune domino effect
Solution Approach 1:
The system pre-calculates and caches protect paths with their associated wavelengths before failures occur. When a link failure is detected, the pre-computed protect path and wavelength are immediately activated without requiring real-time retune calculations, thus eliminating the 30+ second retune delay and preventing domino effects on other services.
Solution Approach 2:
The system maintains a cache of pre-computed protect paths and wavelengths that serve as a buffer against future failures. This cushioning mechanism ensures that when failures occur, restoration can proceed immediately using pre-prepared wavelength assignments, avoiding the need for time-consuming real-time wavelength searches and retunes.
2Reliability
If wavelength retune is performed during service redial, then the service can be restored, but retune domino effect occurs affecting all services in the set
Solution Approach 1:
Protect paths and wavelengths are pre-calculated and cached before failures occur. This preliminary action ensures that wavelength assignments are determined in advance, eliminating the need for sequential retune operations that cause domino effects. The pre-computed paths are stored and immediately applied when failures occur, preventing cascading retune operations.
Solution Approach 2:
The system segments the wavelength allocation process into independent pre-computed protect paths for each service. Each service has its own dedicated protect path with a pre-assigned wavelength, preventing the retune operation of one service from triggering retunes in other services. This segmentation breaks the domino effect chain by making wavelength assignments independent and non-cascading.
3Reliability
If wavelength retune is performed in distributed control plane, then services can be restored, but services may enter non-converging retune loops due to wavelength contention
Solution Approach 1:
Protect paths and wavelengths are pre-calculated and cached before failures occur. This preliminary computation ensures that wavelength assignments are determined in advance with full knowledge of network state, eliminating the need for iterative retune operations that can create loops. The pre-computed paths are stored and immediately applied when failures occur, ensuring convergence without loops.
Solution Approach 2:
The system introduces a centralized path computation element that acts as an intermediary to pre-compute and cache protect paths. This intermediary coordinates wavelength assignments across the distributed control plane before failures occur, ensuring that protect paths are loop-free and converge properly. The cached protect paths serve as a mediator that prevents retune loops during actual restoration operations.
4Loss of time
If protect paths are determined with existing wavelengths first, then wavelength retuning is minimized, but additional processing is required to find alternative wavelengths for connections that cannot use existing wavelengths
Solution Approach 1:
The system performs preliminary computation of protect paths using existing wavelengths before failures occur and caches these results. This preliminary action minimizes the need for wavelength retunes during actual restoration. The pre-computation phase handles the complexity of finding optimal paths, while the restoration phase simply applies the cached results, effectively separating the complex computation from the time-critical restoration operation.
Data Source
AI summary
A method, in a node operating in a network with a control plane, to optimize wavelength retuning on service redials, includes detecting a failure on a link associated with the node; and, for each affected connections on the link, sending a respective release message to an associated originating node via the control plane, the release message including a protect path and a wavelength, wherein the release message is utilized by the associated originating node to redial the affected connections with the protect path and the wavelength determined by the node, to minimize wavelength retuning on the affected connections.