CWS CWS WLAN Roaming and QoS Questions and Answers 2 — Questions and Answers
Question 1: Which QoS mechanism in 802.11 replaces the legacy DCF for differentiated traffic handling?
- EDCA (Enhanced Distributed Channel Access) (Correct answer)
- HCCA (HCF Controlled Channel Access)
- PCF (Point Coordination Function)
- RTS/CTS
Correct answer: EDCA (Enhanced Distributed Channel Access)
EDCA is the contention-based QoS mechanism introduced with 802.11e that provides differentiated channel access for four traffic categories.
Question 2: What roaming threshold metric do most enterprise WLAN controllers use to trigger a client roam?
- RSSI below a configured dBm threshold (Correct answer)
- AP CPU utilization above 80%
- Client IP address conflict
- Channel utilization above 50%
Correct answer: RSSI below a configured dBm threshold
Enterprise controllers monitor client RSSI and trigger load-balancing or roam suggestions when signal drops below a configured threshold.
Question 3: In 802.11r, what is stored in the PMK-R0 key holder?
- The top-level fast transition key derived from the master session key (Correct answer)
- The per-packet encryption key
- The pairwise master key for a single AP
- The RADIUS server certificate
Correct answer: The top-level fast transition key derived from the master session key
PMK-R0 is the top-level key in the 802.11r key hierarchy, stored at the R0 Key Holder (typically the WLAN controller).
Question 4: Which TXOP parameter in WMM defines the maximum time a station may transmit after winning channel access?
- TXOP Limit (Correct answer)
- CWmax
- AIFSN
- CWmin
Correct answer: TXOP Limit
The TXOP Limit sets the maximum duration a station can hold the channel and transmit a burst of frames after winning the contention.
Question 5: What is the primary benefit of deploying both 802.11k and 802.11v together in an enterprise WLAN?
- Clients receive neighbor reports AND network-assisted roaming suggestions for seamless handoffs (Correct answer)
- Higher throughput via channel bonding
- Stronger encryption during roaming
- Reduced beacon overhead
Correct answer: Clients receive neighbor reports AND network-assisted roaming suggestions for seamless handoffs
802.11k provides neighbor lists and 802.11v enables the network to direct clients to better APs, together enabling intelligent, low-latency roaming.
Question 6: What does DSCP marking accomplish for wireless QoS in a unified wired/wireless network?
- Maps IP-layer traffic priority to WMM Access Categories across the wired-wireless boundary (Correct answer)
- Assigns static channels to APs
- Configures RADIUS authentication priority
- Encrypts QoS tags at Layer 2
Correct answer: Maps IP-layer traffic priority to WMM Access Categories across the wired-wireless boundary
DSCP values in IP headers can be mapped to WMM ACs at the AP, allowing end-to-end QoS across wired and wireless segments.
CWS CWS WLAN Roaming and QoS Questions and Answers 2
Which QoS mechanism in 802.11 replaces the legacy DCF for differentiated traffic handling?