Layer 1 Layer 2 Protection Switching Coordination
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Solution Overview
Problem
Conventional approaches to avoid sympathetic switches at Layer 2 during Layer 1 protection or maintenance activities in optical networks delay fault propagation, leading to inefficient Layer 2 protection mechanisms that are not always guaranteed and assume constant Layer 1 protection availability.
Innovation Solution
A method for coordinating Layer 1 and Layer 2 protection switching by communicating defects and recovery actions between Layer 1 and Layer 2 networks using Connectivity Fault Management (CFM) frames with added information, allowing for dynamic Layer 2 protection coordination based on Layer 1 recovery actions, such as preventing, timing, or immediate switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hold-off timer is used to delay Layer 1 defect propagation to Layer 2, then sympathetic switches at Layer 2 are avoided, but Layer 2 protection response time is increased
Solution Approach 1:
The patent applies preliminary action by notifying Layer 2 of Layer 1 defects immediately through CFM messages, but Layer 2 protection switching is conditionally delayed based on the hold-off timer status and recovery action information. This allows Layer 2 to be aware of the defect upfront while controlling the actual switching timing to avoid sympathetic switches.
Solution Approach 2:
The patent implements feedback by including recovery action information in CFM messages sent from Layer 1 to Layer 2. This feedback mechanism allows Layer 2 to understand whether Layer 1 is attempting recovery, enabling intelligent decision-making about whether to trigger protection switching at Layer 2.
2Reliability
If CCM timeout is set greater than mesh restoration time, then Layer 2 protection operates after Layer 1 recovery, but failure detection for Ethernet segments is significantly delayed
Solution Approach 1:
The patent applies preliminary action by sending CFM defect notification messages immediately when Layer 1 defects are detected, without waiting for CCM timeout. This allows Layer 2 to detect failures immediately and prepare for potential protection switching, rather than waiting for the extended CCM timeout period.
Solution Approach 2:
The patent introduces CFM messages as an intermediary mechanism between Layer 1 and Layer 2 for defect notification. This intermediary allows defect information to be transmitted immediately through a dedicated channel, bypassing the slow CCM timeout mechanism while still maintaining coordination with Layer 1 recovery actions.
3Speed
If Layer 2 protection operates independently without Layer 1 coordination, then Layer 2 protection speed is improved, but sympathetic switches cannot be avoided
Solution Approach 1:
The patent implements feedback by sending recovery action information from Layer 1 to Layer 2 through CFM messages. This allows Layer 2 to make informed decisions about protection switching based on Layer 1's recovery status, avoiding sympathetic switches while maintaining fast response through independent operation.
Solution Approach 2:
The patent applies dynamics by making Layer 2 protection switching behavior adaptive based on received CFM messages. When recovery actions are detected, Layer 2 can dynamically adjust its switching behavior to coordinate with Layer 1, while maintaining the ability to operate independently and quickly when no coordination is needed.
Data Source
AI summary
Systems and methods of coordinating Layer 1 and Layer 2 protection switching include, at a node having a plurality of ports including a first port that is an endpoint of a Layer 1 network and a second port that connects to a Layer 2 network, communicating defects in the Layer 1 network to a local Maintenance End Point (MEP) on the second port and any recovery actions being performed in the Layer 1 network; informing other nodes on the Layer 2 network via the second port of the defects and the recovery actions; and coordinating Layer 2 protection switching in the Layer 2 network based on the defects and based on the recovery actions in the Layer 1 network.