CWNA Quality Control & Assurance 4 — Questions and Answers
Question 1: A WLAN QA report flags several APs with beacon interval set to 500 TUs instead of the default 100 TUs. What is the MOST likely negative effect on clients?
- Clients take longer to discover the network and may miss power-save buffered frames (Correct answer)
- Throughput per client increases because less management overhead is generated
- Security is weakened because beacons carry encryption keys
- Roaming triggers are sent less frequently, improving stability
Correct answer: Clients take longer to discover the network and may miss power-save buffered frames
A long beacon interval means clients scanning for networks must wait longer, and power-save clients may miss DTIM notifications for buffered unicast/multicast frames.
Question 2: Which QoS access category (AC) should be used for voice traffic in WMM to achieve the lowest latency?
- AC_VO (Voice) (Correct answer)
- AC_VI (Video)
- AC_BE (Best Effort)
- AC_BK (Background)
Correct answer: AC_VO (Voice)
AC_VO has the shortest AIFS and smallest CWmin/CWmax values, giving voice traffic the highest probability of winning medium access quickly.
Question 3: A site survey validation shows strong –60 dBm RSSI throughout a warehouse, but VoIP quality remains poor. What should the engineer investigate next?
- Latency, jitter, and packet loss (PHY/MAC-layer retransmissions) (Correct answer)
- Number of SSIDs configured per AP
- DHCP lease time for VoIP phones
- Frequency of AP firmware updates
Correct answer: Latency, jitter, and packet loss (PHY/MAC-layer retransmissions)
Strong RSSI rules out coverage as the cause; poor VoIP quality despite good signal indicates MAC-layer issues like high retries, elevated jitter, or excessive latency.
Question 4: During a WLAN audit, an engineer observes that several 5 GHz APs are performing Dynamic Frequency Selection (DFS) channel changes frequently. What is the MOST likely cause?
- A radar source such as weather radar or military radar is being detected nearby (Correct answer)
- Client density on those channels is too high
- The APs are rebooting due to a power issue
- WPA2-Enterprise authentication is triggering DFS events
Correct answer: A radar source such as weather radar or military radar is being detected nearby
DFS channels must be vacated within 10 seconds of radar detection; frequent channel changes indicate persistent radar pulses in the environment.
Question 5: What is the purpose of a post-installation (validation) site survey compared to a pre-deployment (predictive) site survey?
- It verifies that actual RF coverage, capacity, and performance meet design requirements after APs are installed (Correct answer)
- It models expected RF propagation before any hardware is ordered
- It documents channel plans before installation begins
- It captures client device inventory for license management
Correct answer: It verifies that actual RF coverage, capacity, and performance meet design requirements after APs are installed
A post-installation survey uses active or passive measurements with real hardware in place to confirm the deployment matches the design intent.
Question 6: A QA engineer needs to verify 802.11 frame exchange sequences to troubleshoot an association failure. Which tool is BEST suited for this task?
- Protocol analyzer (wireless packet capture tool) (Correct answer)
- Spectrum analyzer
- SNMP MIB browser
- RF heat-mapping application
Correct answer: Protocol analyzer (wireless packet capture tool)
A protocol analyzer captures and decodes 802.11 management, control, and data frames, allowing detailed inspection of the association and authentication exchange.
Question 7: When assessing WLAN quality in a healthcare environment, which coverage threshold is commonly recommended for voice-grade Wi-Fi calling?
- Minimum –67 dBm RSSI with SNR ≥ 25 dB (Correct answer)
- Minimum –80 dBm RSSI with SNR ≥ 10 dB
- Minimum –55 dBm RSSI with SNR ≥ 5 dB
- Minimum –90 dBm RSSI with SNR ≥ 15 dB
Correct answer: Minimum –67 dBm RSSI with SNR ≥ 25 dB
Voice applications require strong, consistent signals; –67 dBm RSSI with at least 25 dB SNR is the widely accepted minimum for reliable Wi-Fi voice quality.
CWNA Quality Control & Assurance 4
A WLAN QA report flags several APs with beacon interval set to 500 TUs instead of the default 100 TUs.
What is the MOST likely negative effect on clients?