PON Protection Switching with Rangeless ONU Failover Timing
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Solution Overview
Problem
Conventional Type B PON protection switching requires re-ranging all ONUs during switchover, causing traffic disruptions due to overlapping upstream transmissions from different ONUs with varying distances, leading to significant downtime.
Innovation Solution
Implement a rangeless failover mechanism where the standby OLT uses a larger guard time based on the primary OLT's differential propagation delay to prevent overlapping transmissions, allowing in-service micro-ranging of ONUs without complete re-registration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Type B PON protection switching is used with re-ranging of all ONUs, then reliability is improved through redundancy, but loss of time increases due to traffic disruptions lasting several hundred milliseconds to seconds
Solution Approach 1:
The standby OLT pre-calculates and stores the differential propagation delay time based on ranging information received from the primary OLT before switchover occurs. This preliminary preparation allows the standby OLT to immediately apply the correct guard time adjustment upon activation, eliminating the need for time-consuming re-ranging operations and enabling fast protection switching within 250 ms or less
Solution Approach 2:
The invention changes the guard time parameter dynamically based on the differential propagation delay. The standby OLT adjusts the guard time by adding the pre-calculated differential time to the normal guard time, allowing upstream transmissions from ONUs at different distances to be properly separated without overlapping, thus enabling fast switchover without complete re-ranging
2Measurement precision
If complete re-ranging of ONUs is performed during switchover, then transmission timing accuracy is improved, but productivity decreases due to traffic loss and service interruption
Solution Approach 1:
Instead of performing complete re-ranging of all ONUs, the invention applies partial action by only adjusting the guard time parameter using pre-calculated differential propagation delay. This partial adjustment is sufficient to prevent transmission overlaps and maintain timing accuracy, while avoiding the service disruption caused by complete re-ranging operations
Solution Approach 2:
The primary OLT performs ranging measurements and calculates differential propagation delay times in advance, storing this information for use by the standby OLT. This preliminary action ensures that when switchover occurs, the standby OLT already has the precise timing information needed to maintain upstream transmission accuracy without requiring time-consuming re-ranging
3Reliability
If guard time is increased to accommodate different ONU distances from standby OLT, then overlapping transmissions are prevented, but bandwidth efficiency decreases
Solution Approach 1:
The invention applies local quality by making the guard time adjustment specific to the differential propagation delay condition. Instead of uniformly increasing guard time for all ONUs, the standby OLT applies a targeted adjustment based on the pre-calculated differential time, which is the minimum necessary to prevent overlaps. This localized adjustment maintains transmission reliability while minimizing bandwidth efficiency loss
Data Source
AI summary
Rangeless failover in Passive Optical Network (PON) protection switching is implemented by an Optical Line Terminal (OLT) that includes a transmitter configured to connect a plurality of Optical Network Units (ONUs) on a downstream channel; a receiver configured to connect the plurality of ONUs on an upstream channel; and circuitry communicatively coupled to the transmitter and the receiver, wherein the circuitry is configured to, responsive to protection switch from a primary OLT, enable the transmitter on the downstream channel, and utilize a Dynamic Bandwidth Assignment (DBA) function on the downstream channel with a guard time that includes a normal guard time plus a differential time added thereto. The guard time is larger than a guard time used by the primary OLT prior to the protection switch. The differential time can be based on a differential between a closest ONU and farthest ONU, relative to the primary OLT, prior to the protection switch.