CWDP CWDP QoS and Voice/Video over WLAN 1 — Questions and Answers
Question 1: Which IEEE standard defines Quality of Service mechanisms for WLANs, including EDCA and TXOP?
- IEEE 802.11e (Correct answer)
- IEEE 802.11r
- IEEE 802.11k
- IEEE 802.11v
Correct answer: IEEE 802.11e
IEEE 802.11e introduced QoS enhancements including Enhanced Distributed Channel Access (EDCA) and transmission opportunity (TXOP).
Question 2: In WMM (Wi-Fi Multimedia), which access category has the highest priority?
- Best Effort (AC_BE)
- Background (AC_BK)
- Video (AC_VI)
- Voice (AC_VO) (Correct answer)
Correct answer: Voice (AC_VO)
AC_VO (Voice) has the shortest arbitration inter-frame spacing and smallest contention window, giving it highest channel access priority.
Question 3: What is the primary purpose of TXOP (Transmission Opportunity) in 802.11e?
- Allow a station to transmit multiple frames within a bounded time period (Correct answer)
- Increase the DIFS interval for high-priority traffic
- Assign IP DSCP values to wireless frames
- Enable multi-band simultaneous transmission
Correct answer: Allow a station to transmit multiple frames within a bounded time period
TXOP grants a station a time window to send multiple frames back-to-back after winning channel access, reducing per-frame overhead.
Question 4: What one-way latency budget is recommended for VoIP over WLAN to maintain acceptable call quality?
- Less than 50 ms
- Less than 150 ms (Correct answer)
- Less than 400 ms
- Less than 1 second
Correct answer: Less than 150 ms
ITU G.114 recommends one-way latency under 150 ms for toll-quality voice; exceeding this degrades call quality noticeably.
Question 5: How does DSCP markings relate to WMM access categories in a Voice over WLAN deployment?
- DSCP values are ignored by wireless APs
- APs map DSCP values to WMM AC queues for traffic prioritization (Correct answer)
- WMM replaces DSCP in all enterprise deployments
- DSCP is only used for wired uplink QoS
Correct answer: APs map DSCP values to WMM AC queues for traffic prioritization
APs inspect DSCP markings on incoming IP packets and map them to the appropriate WMM access category queue.
Question 6: Which metric most directly indicates the wireless medium is over-subscribed, degrading VoIP quality?
- High channel utilization above 50% (Correct answer)
- Low noise floor below -90 dBm
- High RSSI above -65 dBm
- Wide channel bandwidth (80 MHz)
Correct answer: High channel utilization above 50%
Channel utilization above 50% indicates heavy contention, increasing latency and jitter that degrade real-time voice traffic.
CWDP CWDP QoS and Voice/Video over WLAN 1
Which IEEE standard defines Quality of Service mechanisms for WLANs, including EDCA and TXOP?