hardMultiple ChoiceObjective-mapped
220-1201 Practice Question: A technician is troubleshooting a fiber optic…
A technician is troubleshooting a fiber optic connection where the ONT (Optical Network Terminal) has a red 'LOS' (Loss of Signal) light. The fiber cable appears intact. What should the technician check next?
⚠ Common exam trap
A common misconception is that a red LOS light means the ONT is faulty or that rebooting the router will fix the fiber link, when in fact the LOS indicator is purely optical and requires cleaning or verifying the physical connection first.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Inspect and clean the fiber connector.
A red LOS (Loss of Signal) light on the ONT indicates that no light is being received from the optical line terminal (OLT) at the central office. Since the fiber cable appears intact, the most likely cause is a dirty or damaged connector at the ONT or the wall jack, which can attenuate the optical signal below the receiver threshold. Cleaning the fiber connector with a proper one-click cleaner or inspection scope is the standard next step before considering hardware replacement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace the ONT immediately.
Why it's wrong here
Replacing the Optical Network Terminal (ONT) immediately is a premature troubleshooting step when the Loss of Signal (LOS) light is illuminated. The LOS indicator specifically points to an absence or severe degradation of the incoming optical signal from the service provider's network, which is an upstream physical layer issue. Without further diagnostics to rule out simpler causes like a dirty connector or a cable fault, replacing the entire device is inefficient and likely unnecessary, as the ONT itself may be functioning correctly but simply not receiving a signal.
- ✗
Check the power supply to the ONT.
Why it's wrong here
Checking the power supply to the ONT is incorrect because the presence of the illuminated Loss of Signal (LOS) light explicitly confirms that the ONT is receiving power. If the ONT were experiencing a power supply issue, there would be no lights illuminated on the device at all, as it would be completely inoperable. The LOS light indicates that the device has power and is actively detecting the absence of an expected optical signal.
- ✓
Inspect and clean the fiber connector.
Why this is correct
Inspecting and cleaning the fiber connector is the most appropriate initial troubleshooting step when the Loss of Signal (LOS) light is on. The LOS indicator signifies that the ONT is not receiving the expected optical signal from the fiber optic cable. Contamination, dust, or minor damage on the end face of a fiber optic connector is an extremely common cause of signal attenuation or complete loss, and a thorough, proper cleaning often restores the connection without further intervention.
- ✗
Reboot the router connected to the ONT.
Why it's wrong here
Rebooting the router connected to the ONT will not resolve an issue indicated by the ONT's Loss of Signal (LOS) light. The router operates at a higher network layer (Layer 3, Network Layer) and is responsible for IP address assignment and routing data packets. The LOS light on the ONT, however, signifies a fundamental physical layer (Layer 1) problem, indicating the absence of the optical signal itself, which occurs before the router can even begin to process network traffic.
Go deeper
Related to this question
Learn chapter
Laptop Hardware and Components
Key term
Optical Network Terminal
An Optical Network Terminal (ONT) is a device that connects your home or office to the internet service provider's fiber optic network, converting light signals into electrical signals your devices can use.
Key term
Receiver
A receiver is a hardware device or software component that accepts incoming signals, data, or transmissions from a sender over a communication channel.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.