CWS CWS MAC Layer Functions 3

Question 1

WMM (Wi-Fi Multimedia) defines four Access Categories (ACs). Which AC has the HIGHEST priority?

Accepted Answer

AC_VO (Voice)

Answer

AC_VO (Voice) has the highest priority under WMM, using the smallest AIFS and contention window values to gain channel access fastest.

Question 2

In 802.11e/WMM, what replaces the standard DIFS as the mandatory idle time before a station transmits in a QoS-enabled network?

Accepted Answer

AIFS (Arbitration Inter-Frame Space)

Answer

AIFS (Arbitration Inter-Frame Space) replaces DIFS in EDCA; each Access Category has its own AIFS value, with higher-priority ACs using shorter AIFS values.

Question 3

What is a TXOP (Transmission Opportunity) in 802.11 QoS?

Accepted Answer

A bounded time interval during which a station may send multiple frames

Answer

A TXOP grants a station a bounded time window in which it can send multiple frames without re-contending for the channel after each frame.

Question 4

EDCA (Enhanced Distributed Channel Access) is part of which 802.11 amendment?

Accepted Answer

802.11e

Answer

802.11e introduced EDCA and the full QoS framework (HCF), which WMM is based upon.

Question 5

Which WMM Access Category maps to the 802.1p priority values 0 and 3 (best effort and video)?

Accepted Answer

AC_BE and AC_VI respectively

Answer

802.1p UP 0 maps to AC_BE (Best Effort) and UP 3 maps to AC_VI (Video) in the WMM Access Category mapping table.

CWS Exam Practice Test

CWS Exam Practice Test

CWS CWS MAC Layer Functions 3