CWNA Quality Control & Assurance 3 — Questions and Answers
Question 1: An enterprise WLAN shows high retry rates (>20%) across multiple APs. Which condition MOST likely explains this?
- Co-channel interference causing frame collisions (Correct answer)
- Incorrect DHCP lease time configuration
- Too many SSIDs broadcasting on each AP
- WPA3-SAE authentication overhead
Correct answer: Co-channel interference causing frame collisions
Co-channel interference causes multiple devices to transmit simultaneously, resulting in collisions that require frame retransmission and drive up retry rates.
Question 2: A wireless QA test reveals that roaming latency between APs exceeds 300 ms, disrupting VoIP calls. Which 802.11 amendment is specifically designed to reduce roaming latency?
- 802.11r (Fast BSS Transition) (Correct answer)
- 802.11k (Radio Resource Management)
- 802.11v (BSS Transition Management)
- 802.11u (Interworking with External Networks)
Correct answer: 802.11r (Fast BSS Transition)
802.11r pre-caches PMK key material between APs so clients can complete the four-way handshake faster during roaming, reducing handoff latency.
Question 3: During a wireless audit, an engineer discovers hidden nodes causing throughput degradation. Which 802.11 mechanism addresses hidden node problems?
- RTS/CTS handshake (Correct answer)
- CSMA/CA backoff algorithm
- OFDM guard intervals
- MU-MIMO spatial streams
Correct answer: RTS/CTS handshake
RTS/CTS causes stations to reserve the medium before transmitting, so hidden nodes that cannot hear each other are made aware of ongoing transmissions through CTS frames.
Question 4: A network QA team measures per-AP airtime fairness and finds legacy 802.11b clients at 1 Mbps are consuming disproportionate airtime. What is the recommended corrective action?
- Enable minimum basic rate of 11 Mbps or higher to disassociate legacy clients (Correct answer)
- Increase AP transmit power to speed up legacy client frames
- Change channel width from 20 MHz to 40 MHz
- Enable SSID hiding to prevent legacy clients from associating
Correct answer: Enable minimum basic rate of 11 Mbps or higher to disassociate legacy clients
Raising the minimum basic rate excludes clients that cannot support faster rates, preventing slow legacy devices from monopolizing airtime.
Question 5: Which tool provides the MOST detailed information about non-802.11 RF interference in a specific frequency band?
- Spectrum analyzer (Correct answer)
- Protocol analyzer (packet sniffer)
- Wi-Fi scanner application
- SNMP-based network management system
Correct answer: Spectrum analyzer
A spectrum analyzer displays raw RF energy across frequencies regardless of source, allowing identification of non-802.11 interferers that packet analyzers cannot decode.
Question 6: A QA engineer validates a WLAN design using the 3-AP rule for 802.11 location services. What does this rule specify?
- A client must be in range of at least 3 APs simultaneously for accurate triangulation (Correct answer)
- Each AP must support at least 3 spatial streams for location accuracy
- Location updates must occur at least 3 times per second
- Each floor must have at least 3 APs regardless of size
Correct answer: A client must be in range of at least 3 APs simultaneously for accurate triangulation
Location triangulation (RSSI-based) requires signal from at least 3 APs to compute a client's 2D position; fewer APs degrade accuracy significantly.
Question 7: After a firmware upgrade, channel utilization on 5 GHz APs spikes to 90%. The administrator suspects transmit power levels were reset to defaults. What unintended consequence does excessively high AP transmit power cause?
- AP-to-AP co-channel interference increases, raising channel utilization (Correct answer)
- Client authentication times decrease significantly
- Beacon intervals become shorter, flooding the medium
- DFS channels are automatically disabled
Correct answer: AP-to-AP co-channel interference increases, raising channel utilization
Excessively high AP transmit power causes nearby APs on the same channel to hear each other strongly, forcing CCA deferral and increasing channel utilization without improving client performance.
CWNA Quality Control & Assurance 3
An enterprise WLAN shows high retry rates (>20%) across multiple APs.
Which condition MOST likely explains this?