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300-365 · Question #90
300-365 Question #90: Real Exam Question with Answer & Explanation
The correct answer is A: AC_VO. Under 802.11e/WMM, TXOP (Transmission Opportunity) grants a station a bounded time window to send multiple frames; only AC_VO and AC_VI are assigned non-zero TXOP values by default to support time-sensitive traffic.
Question
Which two access categories could use TXOP value higher than 0, as per 802.11e standard? (Choose two.)
Options
- AAC_VO
- BAC_BK
- CAC_VI
- DAC_BE
- EAC_NC
Explanation
Under 802.11e/WMM, TXOP (Transmission Opportunity) grants a station a bounded time window to send multiple frames; only AC_VO and AC_VI are assigned non-zero TXOP values by default to support time-sensitive traffic.
Common mistakes.
- B. AC_BK (Background) has a TXOP limit of 0 in the standard EDCA defaults, meaning each transmission requires a separate channel contention cycle.
- D. AC_BE (Best Effort) also has a TXOP limit of 0 by default, as best-effort traffic does not require the burst transmission efficiency that voice and video need.
- E. AC_NC is not a defined 802.11e access category; the standard defines only AC_VO, AC_VI, AC_BE, and AC_BK.
Concept tested. 802.11e WMM TXOP limits per access category
Reference. https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob41dg/ch7_QoS.html
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