300-365 · Question #90
Which two access categories could use TXOP value higher than 0, as per 802.11e standard? (Choose two.)
The correct answer is A. AC_VO C. AC_VI. 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
How the community answered
(33 responses)- A88% (29)
- B6% (2)
- D3% (1)
- E3% (1)
Why each option
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.
AC_VO (Voice) is assigned a non-zero TXOP limit in the 802.11e EDCA parameter set, allowing a voice client to transmit multiple frames back-to-back within the granted interval to minimize latency and jitter.
AC_BK (Background) has a TXOP limit of 0 in the standard EDCA defaults, meaning each transmission requires a separate channel contention cycle.
AC_VI (Video) is also assigned a non-zero TXOP limit so that video streams can burst several frames within one contention win, reducing interruptions from repeated channel contention.
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.
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
Source: https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob41dg/ch7_QoS.html
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