Alien Signal Injection Detection in Passive Optical Networks
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Solution Overview
Problem
In passive optical networks, there is no effective mechanism to identify the source of interfering upstream signals that degrade communication quality, particularly in cases of denial of service attacks, as existing systems cannot determine which branch of the network is causing the issue.
Innovation Solution
A method that involves stopping downstream transmissions and detecting which network branch continues to receive upstream signals, allowing the identification of the source of the interfering signal by interrupting downstream OLT transmissions and using active optical-electrical-optical converters to monitor and isolate the affected branch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing PON systems monitor optical communication channels to detect signal degradation, then signal degradation can be detected, but the source of the interfering signal cannot be determined
Solution Approach 1:
The patent segments the optical distribution network into multiple network branches, each connected to a second port of the branching device. By stopping downstream transmissions selectively and detecting upstream signals on individual branches, the system divides the problem of source identification into manageable per-branch assessments, enabling precise localization of the interfering signal source.
Solution Approach 2:
The patent introduces an intermediary detection mechanism at the branching device that monitors upstream signals from each network branch independently. This intermediary detection capability acts as a mediator between the OLT and the distributed ONTs, providing the missing information about which specific branch is transmitting interfering signals without requiring direct communication between the OLT and each ONT.
2Reliability
If a malicious ONT emits interfering signals in the upstream channel, then communication quality degrades, but there is no mechanism to identify which branch is the source
Solution Approach 1:
The patent divides the upstream channel monitoring into separate per-branch assessments. By stopping downstream transmissions on specific branches and detecting whether upstream signals persist, the system segments the detection process to identify which specific network branch contains the malicious ONT emitting interfering signals.
Solution Approach 2:
The patent applies preliminary anti-action by proactively stopping downstream transmissions on network branches before detecting the presence of interfering upstream signals. This preventive measure allows the system to isolate and identify malicious branches before they can degrade overall communication quality across the entire network.
3Adaptability or versatility
If active branching devices are used to enable efficient OLT usage, then network flexibility improves, but the complexity of the system increases
Solution Approach 1:
The patent makes the branching device universal by equipping it with dual functionality: traditional signal splitting/combining and active upstream signal detection. The branching device can perform both passive optical switching and active monitoring of upstream signals from each network branch, reducing the need for separate dedicated detection equipment and simplifying the overall system architecture.
Solution Approach 2:
The patent merges the signal switching function and the signal detection function into a single branching device. By combining these functions, the system reduces device complexity and interconnections while maintaining the ability to both configure network branches flexibly and identify interfering signal sources.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the localization of malfunctioning or misbehaving ONTs, thereby allowing for appropriate countermeasures to be taken, such as isolating the affected branch, and restoring service once the interfering signal is removed.
Implementation Method 1
Active branching devices not only perform a splitting/combining function but also include optical-electrical-optical converter switch that convert the optical signals arriving at the device from the optical domain to the electrical domain and back again
Data Source
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AI summary
The location of a source (X) of an alien signal propagating upstream in a passive optical network (1) is identified by a method which cuts off downstream signals from an optical line terminal (2) to the branches (5) of the optical network and detects which network branch (5x) is still propagating a signal upstream despite the absence of downstream signals. A1-to-N branching device (4) comprising active optical-electrical-optical converters (41,42) implements the source-localization method by: controlling active converters of the branching device to cut off the downstream transmissions from the OLT (2), and detecting signal power on a particular network branch (5x) after the OLT transmissions have been interrupted. The branching device (4) may isolate the offending network branch (5x) from the OLT (2) using the active converter (42) connected to this network branch (5x) and may notify the OLT (2) of the offending port (Bx) or network branch (5x). The branching device (4) may monitor upstream signals from the offending network branch (5x) and re-connect the network branch (5x) if the interfering upstream signals disappear.