Backup OLT De Minimis Time Slot Allocation for Fast Failover
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Solution Overview
Problem
Current optical network failover systems in PONs experience delays exceeding 50 milliseconds during failover switches, which violate service level agreements, especially when the primary OLT cannot communicate with the backup OLT due to failures like power loss, leading to prolonged downtime.
Innovation Solution
Implementing a backup OLT that allocates small 'de minimis' upstream time slots to ONTs during normal operation, allowing ONTs to autonomously tune to the backup OLT's wavelength upon failure, enabling quick failover by transmitting data in these slots, which the backup OLT recognizes to initiate normal time-slot allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ONTs wait for registration period to communicate with backup OLT, then failover switch can be performed, but failover delay exceeds service level agreements
Solution Approach 1:
The backup OLT is pre-configured with ONT identifiers and communication parameters before failure occurs. De minimis time slots are pre-allocated for potential failover communication. This preliminary preparation eliminates the need for lengthy registration procedures during actual failover, reducing delay from seconds to milliseconds.
Solution Approach 2:
The patent extracts the essential failover communication capability from the full registration process. Instead of requiring complete registration during failover, the system uses pre-configured information and minimal de minimis time slots to enable immediate communication with the backup OLT, separating the critical failover function from the complete registration procedure.
2Reliability
If primary OLT cannot communicate with backup OLT due to failure, then failover is necessary, but notification to backup OLT cannot be provided
Solution Approach 1:
The ONTs autonomously detect primary OLT failure and self-initiate failover to the backup OLT without requiring notification from the primary OLT. The ONTs use pre-configured backup OLT information to autonomously establish communication, eliminating the dependency on primary OLT notification mechanisms that may be compromised during failure.
Solution Approach 2:
The patent introduces an intermediary monitoring mechanism that detects primary OLT communication failures and triggers failover. This intermediary layer separates the failure detection function from the primary OLT itself, allowing failover initiation even when the primary OLT cannot communicate with the backup OLT.
3Speed
If de minimis time slots are allocated to ONTs, then quick failover detection is enabled, but upstream bandwidth is consumed during normal operation
Solution Approach 1:
The de minimis time slots are allocated with locally optimized characteristics - they are extremely brief and used only for critical failover detection purposes. During normal operation, these slots consume minimal bandwidth, but provide rapid failover capability when needed. The local quality of these time slots is tailored specifically for fast detection rather than general data transmission.
Solution Approach 2:
The system uses a small number of partial de minimis time slots rather than full allocation. These minimal slots are sufficient for failover detection purposes without excessively consuming upstream bandwidth during normal operation. The action is calibrated to be just enough for the critical function of failover detection.
Data Source
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AI summary
A system for performing failover switches in an optical network, such as a time and wavelength division passive optical networks (TWDM PON) like NG-PON2, includes a backup optical line terminal (OLT) for backing up communications of a primary OLT. The backup OLT is configured to allocate small upstream time slots, referred to herein as "de minimis" time slots, to at least one optical network terminal (ONT) communicating with the primary OLT during normal operation. When a failure occurs that prevents communication between the ONT and the primary OLT, the ONT autonomously tunes to the upstream and downstream wavelength pairs of the backup OLT and begins to transmit data to the backup OLT in the de minimis time slot allocated to it. The presence of data in the de minimis time slot indicates the occurrence of a failover switch to the backup OLT, and the backup OLT then begins to allocate time slots to this ONT.