EPON Redundancy via Lenient ONU State
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Solution Overview
Problem
Conventional Ethernet passive optical networks (EPONs) face challenges in achieving rapid recovery from failures, with current redundancy techniques taking around 1 second to restore service, which is insufficient for modern applications demanding recovery in under 50 milliseconds, and are limited by co-location of redundant OLTs, synchronization of timestamp counters, and complex security key synchronization.
Innovation Solution
The system introduces a lenient state in ONUs that accepts old and new security keys and updates timestamps, allowing for swift switchover between OLTs in less than 50 milliseconds, with OLTs deployed at diverse locations and asynchronous security information updates, enabling fast recalibration of round trip times and maintenance of independent statistic counters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional redundancy techniques are used with OLT deregistration and re-registration, then service restoration is achieved, but switchover time is too long (approximately 1 second)
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing timestamp counters between standby and active OLTs before failure occurs. The standby OLT continuously maintains synchronized timestamp counters with the active OLT, so when switchover is needed, the timestamp synchronization is already in place, eliminating the need for time-consuming re-synchronization and enabling fast service restoration under 50 milliseconds
Solution Approach 2:
The patent uses an intermediary mechanism where the standby OLT continuously receives and processes timestamp information from the active OLT through a dedicated synchronization interface. This intermediary timestamp synchronization channel allows the standby OLT to maintain accurate timing information without full protocol interaction, enabling rapid switchover while maintaining timestamp accuracy
2Device complexity
If OLTs are co-located to share resources, then device complexity is reduced, but location redundancy is lost
Solution Approach 1:
The patent applies universality by designing the OLT timestamp synchronization mechanism to be location-agnostic. The standby OLT can maintain synchronized timestamp counters regardless of whether it is co-located with or geographically separated from the active OLT. The synchronization protocol works universally across different deployment scenarios, allowing the system to achieve both simplified configuration and location redundancy simultaneously
3Reliability
If timestamp counters are synchronized between OLTs, then service continuity is maintained, but device complexity increases
Solution Approach 1:
The patent extracts the timestamp synchronization function from the full OLT protocol interaction. Instead of requiring complete protocol handshakes and complex coordination mechanisms, the patent isolates and implements only the essential timestamp counter synchronization through a simplified dedicated interface. This extraction reduces device complexity while maintaining service continuity through accurate timestamp synchronization
Data Source
AI summary
A system for redundancy in Ethernet passive optical networks (EPONs) facilitates fast recovery from failure (less than 50 msec), path redundancy of the fiber optic network, and location redundancy of the OLTs. An optical networking unit (ONU) in a normal state monitors input communications, and when the input communications are quiet for a predetermined minimum length of time, the ONU transitions to a lenient state in which: the ONU accepts old and new security keys; upon receiving a packet: the ONU updates an ONU timestamp based on the packet's timestamp; and the ONU transitions to the normal state of operation. While the ONU is in the lenient state if a packet is not received for a predetermined given length of time the ONU transitions to a deregistered state. In this system, main and standby OLTs do not require synchronization of security parameters or synchronization for differences in fiber lengths.