CWS CWS MAC Layer Functions 5

Question 1

The Network Allocation Vector (NAV) is a virtual carrier-sense mechanism. Which event causes a station to SET its NAV timer?

Accepted Answer

Receiving a frame whose Duration field specifies a non-zero reservation time

Answer

When a station receives any 802.11 frame (even if not addressed to it) with a non-zero Duration field, it sets its NAV to that value, treating the medium as busy for virtual carrier sense.

Question 2

RTS/CTS protection is mandatory when the data frame size exceeds the RTS Threshold. What is the primary benefit of using RTS/CTS?

Accepted Answer

It mitigates the hidden node problem by reserving the medium before sending a large data frame

Answer

RTS/CTS allows the transmitter and receiver to exchange short reservation frames so that hidden nodes that may not hear each other will hear at least one of the exchange frames and defer.

Question 3

In 802.11ax (Wi-Fi 6), what MAC mechanism allows the AP to simultaneously trigger multiple stations to transmit on different resource units (RUs)?

Accepted Answer

Multi-User OFDMA with Trigger Frames

Answer

802.11ax introduces Trigger Frames that allow the AP to schedule uplink MU-OFDMA transmissions, letting multiple stations send simultaneously on assigned RUs.

Question 4

What is the EIFS (Extended Inter-Frame Space) and when is it used?

Accepted Answer

A longer IFS a station must wait after receiving a corrupted frame before transmitting

Answer

EIFS is a longer inter-frame space used by a station after it receives a frame with a CRC error, preventing it from interfering with an ongoing exchange it may have partially missed.

Question 5

Which MAC feature was introduced in 802.11n to allow back-to-back frame transmissions with a shorter gap than SIFS, improving aggregate throughput within a TXOP?

Accepted Answer

Reduced Inter-Frame Space (RIFS)

Answer

RIFS (Reduced Inter-Frame Space) at 2 µs is shorter than SIFS and was introduced in 802.11n to allow tighter back-to-back frame bursting within a single TXOP.

CWS Exam Practice Test

CWS Exam Practice Test

CWS CWS MAC Layer Functions 5