Dynamic Wavelength Allocation Control in OLT for TDM/WDM-PON
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Solution Overview
Problem
In TDM/WDM-PON systems with cyclic sleep, the allocation of bandwidth to ONUs in sleep mode leads to a decrease in bandwidth utilization margin, and the number of active ONUs that need management changes increases, causing communication delays due to wavelength changes and signal buffering.
Innovation Solution
A dynamic wavelength allocation control method that prioritizes shifting the management of ONUs in sleep mode to another OSU, minimizing the number of active ONUs to be changed by calculating and comparing bandwidth thresholds, thereby alleviating bandwidth utilization margin deterioration and reducing communication delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bandwidth is allocated to ONUs in sleep mode to maintain PON link, then reliability of communication is improved, but bandwidth utilization margin decreases
Solution Approach 1:
The patent segments the ONU population into sleep mode ONUs and active ONUs, applying different bandwidth allocation strategies to each segment. Sleep mode ONUs receive minimal bandwidth only for link maintenance signals, while active ONUs receive full bandwidth for data transmission, thereby preserving bandwidth utilization margin while maintaining link reliability.
Solution Approach 2:
The patent applies partial action by allocating only the minimum necessary bandwidth to sleep mode ONUs—just enough to maintain the PON link through periodic signal exchange—rather than allocating full bandwidth. This partial allocation suffices for link maintenance while preserving bandwidth for active ONUs.
2Productivity
If management of active ONUs is changed to balance load, then productivity of bandwidth allocation is improved, but loss of time increases due to wavelength changes and signal buffering
Solution Approach 1:
The patent performs preliminary actions by pre-calculating and pre-notifying wavelength change requirements to ONUs before actual management changes occur. This allows ONUs to prepare for wavelength transitions in advance, reducing the actual communication delay during handover. The OLT also pre-allocates bandwidth to minimize disruption to active communications.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that bandwidth allocation and wavelength management changes occur without interrupting active data transmission. The system coordinates wavelength changes and bandwidth reallocation to happen during periods that minimize impact on active ONUs, maintaining continuous data flow while transitioning management.
3Device complexity
If the number of ONUs managed by each OSU is increased to reduce reallocation frequency, then device complexity is reduced, but productivity of bandwidth allocation decreases due to threshold exceedance
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The threshold for determining when to trigger DWA is dynamically adjusted based on current system conditions, including the number of active ONUs, bandwidth utilization patterns, and sleep mode ONU counts. This allows the system to optimize between management complexity and allocation productivity in real-time.
Solution Approach 2:
The patent changes parameters by adjusting the DWA trigger threshold based on the number of sleep mode ONUs. When sleep mode ONUs occupy significant bandwidth, the effective threshold for active ONUs is adjusted downward, triggering DWA earlier to rebalance load. This parameter change allows the system to maintain optimal productivity without excessive reallocation frequency.
Data Source
AI summary
In a TDM/WDM-PON using cyclic sleep, a controller in an OLT calculates the total bandwidth in use for each OSU, and compares the total bandwidth with a threshold. If the calculated bandwidth exceeds the threshold, the controller determines the number of ONUs staying in sleep mode among the ONUs managed by the assignor OSU. If such an ONU exists, that ONU is selected as an ONU whose management is to be changed. From the total bandwidth in use of an assignor OSU from which the management is to be changed, a bandwidth allocated to the ONU which is in sleep mode is subtracted to thereby obtain a bandwidth, which will be compared with the threshold. If the calculated bandwidth exceeds the threshold, from among active ONUs managed by the assignor OSU an ONU whose management is to be changed is selected.