hardMultiple ChoiceObjective-mapped
OTDR: Diagnose Fiber Optic Cable Loss and Faults
A network administrator is troubleshooting a slow connection between two buildings connected by a fiber optic link. The link is up but throughput is lower than expected. Which tool should be used to measure the exact signal loss in the fiber?
Quick Answer
The answer is an optical time-domain reflectometer (OTDR), which is the correct tool to measure exact signal loss in a fiber optic link. An OTDR works by sending a series of light pulses into the fiber and analyzing the backscatter and reflections that return, allowing it to pinpoint the location and severity of loss caused by splices, bends, or damage. On the CompTIA A+ Core 1 220-1201 exam, this question tests your ability to distinguish between tools used for fiber troubleshooting—a common trap is confusing the OTDR with a simple visual fault locator or power meter, which only measure total loss or find gross breaks, not the detailed profile needed for diagnosing throughput issues. Remember the memory tip: OTDR stands for “Optical Time-Domain Reflectometer,” and think of it as the “radar” for fiber—it sends out a pulse and listens for the echo to map every foot of the cable.
⚠ Common exam trap
It's easy for candidates to confuse a 'link being up' with 'no signal loss,' leading them to overlook the need for an OTDR and instead choose a multimeter or tone generator, which are irrelevant to fiber optics.
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
✓
OTDR
An Optical Time-Domain Reflectometer (OTDR) is the correct tool because it sends a series of optical pulses into the fiber and measures the backscattered and reflected light to calculate the exact signal loss (attenuation) at specific points along the link. This allows the administrator to identify splices, bends, or connectors causing excessive loss, which directly explains the low throughput despite the link being up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Multimeter
Why it's wrong here
A multimeter cannot measure optical power or loss in fiber optic cables.
- ✗
Tone generator
Why it's wrong here
A tone generator works with copper cables, not fiber optics.
- ✓
OTDR
Why this is correct
An OTDR is the standard tool for characterizing fiber optic links, measuring loss and locating faults.
- ✗
Wi-Fi analyzer
Why it's wrong here
A Wi-Fi analyzer is for wireless networks and cannot test fiber optics.
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Same concept, more angles
1 more way this is tested on 220-1201
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is troubleshooting intermittent packet loss on a critical link between two buildings. The link uses single-mode fiber optic cable. Which tool is specifically designed to measure the length of the fiber and locate breaks or splices that could cause signal loss?
hard- A.Light meter
- ✓ B.OTDR
- C.Multimeter
- D.Cable tester
Why B: An Optical Time-Domain Reflectometer (OTDR) is the correct tool because it sends a series of light pulses into the fiber and measures the backscattered and reflected light to calculate fiber length, locate breaks, splices, and connectors, and quantify loss at each event. This makes it ideal for troubleshooting intermittent packet loss caused by physical impairments in a single-mode fiber link between buildings.
JA
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.