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CISSP Practice Question: A large hospital uses a wireless LAN (WLAN) for…
A large hospital uses a wireless LAN (WLAN) for mobile medical devices and staff tablets. Recently, nurses reported intermittent connectivity drops and high retransmission rates specifically in the east wing near the elevator banks. The WLAN is based on 802.11ac in the 5 GHz band. The hospital's IT team has already checked for channel overlap, and the APs are configured to use non-overlapping channels with automatic channel selection. Signal strength in the area is adequate (-65 dBm). However, the retransmission rate spikes during peak hours. Which approach should the network team take FIRST to diagnose and resolve the issue?
⚠ Common exam trap
It's easy for candidates to assume retransmissions are caused by congestion or weak signal and jump to adding APs or increasing power, but the specific location (elevator banks) and intermittent nature point to external interference, which requires spectrum analysis 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
✓
Conduct a spectrum analysis to identify sources of interference and reposition APs away from the elevator shafts.
The symptoms—intermittent connectivity drops and high retransmission rates near elevator banks during peak hours—strongly suggest external RF interference, likely from the elevator motors or other electrical equipment. A spectrum analysis is the correct first step because it can identify non-Wi-Fi interference sources (e.g., microwave ovens, motors, or radar) that cause packet corruption and retransmissions, even when signal strength is adequate and channels are non-overlapping. Repositioning APs away from the elevator shafts after identifying the interference source directly mitigates the physical cause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Conduct a spectrum analysis to identify sources of interference and reposition APs away from the elevator shafts.
Why this is correct
Conducting a spectrum analysis is the most effective initial step to diagnose wireless performance issues, especially near potential sources of electromagnetic interference like elevator shafts. A spectrum analyzer can identify non-802.11 interference from sources such as elevator motors, microwave ovens, or cordless phones, which standard Wi-Fi tools cannot detect. By pinpointing the exact frequencies and strength of this interference, administrators can strategically reposition Access Points (APs) to minimize its impact, ensuring optimal signal-to-noise ratio and reliable connectivity for mobile medical devices.
- ✗
Enable frequency hopping on the APs to avoid interference.
Why it's wrong here
Enabling frequency hopping spread spectrum (FHSS) on APs is not a viable solution for modern Wi-Fi networks, as current 802.11 standards (like 802.11ac, commonly used in enterprise environments) utilize Orthogonal Frequency-Division Multiplexing (OFDM) with fixed channel widths. FHSS was primarily used in older 802.11b implementations and is not compatible with contemporary Wi-Fi chipsets and protocols. Therefore, this option is technically infeasible and would not address interference in a modern WLAN.
- ✗
Increase the transmit power of the APs in the east wing to improve signal-to-noise ratio.
Why it's wrong here
Increasing the transmit power of APs is generally an ineffective and potentially detrimental approach to mitigate interference, particularly from external sources like elevator motors. While it might slightly improve signal strength, it does not eliminate the underlying interference and can exacerbate co-channel interference with other APs, leading to increased contention and reduced overall network capacity. Furthermore, higher transmit power can create a 'hidden node' problem, where clients hear the AP but not each other, hindering efficient communication.
- ✗
Deploy additional APs in the elevator area to provide more capacity and redundancy.
Why it's wrong here
Deploying additional APs in an area already experiencing significant interference, such as near elevator shafts, without first identifying and mitigating the interference source, is counterproductive. More APs in a problematic RF environment can lead to increased co-channel interference and contention among devices, degrading performance rather than improving it. The root cause of the poor connectivity is likely external interference, which simply adding more transmitting devices will not resolve and may even worsen.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 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 CISSP exam.