OLT Laser Overlap Detection in Passive Optical Networks
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Solution Overview
Problem
In passive optical networks (PONs), communication interference leading to data loss occurs due to clock drift or malfunctioning of Optical Network Units (ONUs), causing laser overlap and traffic collisions, which existing methods fail to efficiently detect and resolve.
Innovation Solution
The Optical Line Terminal (OLT) monitors packet errors and uses methods to determine if an ONU is causing laser overlap by granting specific transmission windows for REPORT messages, allowing identification of interfering ONUs and potential corrective actions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If time sharing scheme is used to allocate transmission windows to ONUs, then traffic collision is avoided, but data loss occurs due to clock drift and laser overlap
Solution Approach 1:
The patent applies preliminary action by having the OLT send a preliminary gate message to the first ONU before the actual data transmission window. This gate message serves as an advance notification that allows the OLT to monitor whether the ONU will properly adhere to its allocated transmission timing. By performing this preliminary check, the system can identify potential clock drift issues before they cause data loss from laser overlap with other ONUs.
2Productivity
If transmission windows are granted to multiple ONUs, then network capacity is increased, but laser overlap and traffic collision occur due to ONU malfunction or clock drift
Solution Approach 1:
The patent implements feedback by having the OLT monitor whether gate messages sent to ONUs are properly acknowledged and whether transmission windows are adhered to. When the OLT detects that a gate message is missed or that an ONU is transmitting outside its allocated window, it generates feedback information identifying the problematic ONU. This feedback mechanism allows the system to maintain high network capacity by continuing to serve multiple ONUs while actively detecting and reporting laser overlap conditions that would otherwise go unnoticed.
3Reliability
If clock synchronization is maintained among ONUs, then traffic collision is prevented, but data loss occurs when ONU clock drifts or malfunctions
Solution Approach 1:
The patent uses the gate message as an intermediary mechanism between the OLT and ONUs to detect timing violations. Rather than relying solely on direct ONU-to-ONU synchronization, the gate message serves as a mediator that allows the OLT to verify whether each ONU is properly adhering to its allocated transmission window. This intermediary approach enables the system to maintain synchronization while detecting when individual ONUs drift from their assigned time slots, preventing data loss from laser overlap.
Data Source
AI summary
There are disclosed systems and methods for detecting whether an Optical Network Unit (ONU) in a network may be causing a communications interference due to laser overlap. In one embodiment, an Optical Line Terminal (OLT) selects a pair of ONUs suspected of possibly causing laser overlap. The OLT then grants a first window to a first ONU for transmitting a first message, and grants to another ONU different from the pair of ONUs a second window for transmitting a second message. If the first message is not received by the OLT, then the OLT indicates that the first ONU may be causing laser overlap. In another embodiment, the OLT grants to an ONU a window for transmitting a message to the OLT. If the message is not received by the OLT when expected, then the OLT indicates that the ONU may be causing laser overlap. Other embodiments are disclosed.