CWS CWS MAC Layer Functions 4

Question 1

In legacy 802.11 Power Save Mode (PSM), how does a sleeping station learn that the AP has buffered frames waiting for it?

Accepted Answer

The station checks the Traffic Indication Map (TIM) in the beacon

Answer

The AP includes a TIM (Traffic Indication Map) in each beacon; a sleeping station wakes up periodically to read the beacon and checks whether its AID bit is set, indicating buffered frames.

Question 2

What is the function of an IBSS ATIM window in an ad-hoc (IBSS) network power-save operation?

Accepted Answer

A period at the start of each beacon interval during which stations announce buffered frames to sleeping peers

Answer

In an IBSS, the ATIM (Announcement Traffic Indication Message) window immediately follows each beacon; stations transmit ATIM frames to notify sleeping peers of buffered data.

Question 3

Frame aggregation in 802.11n/ac/ax can combine multiple MSDUs or MPDUs into a single transmission. Which type aggregates multiple MPDUs with a shared PHY header?

Accepted Answer

A-MPDU

Answer

A-MPDU (Aggregated MAC Protocol Data Unit) combines multiple MPDUs under a single PHY preamble, significantly increasing throughput efficiency.

Question 4

What is the maximum A-MSDU size allowed in 802.11n when the 'Large A-MSDU' capability is negotiated?

Accepted Answer

7,935 bytes

Answer

When Large A-MSDU is negotiated in 802.11n, the maximum A-MSDU size is 7,935 bytes, compared to the default 3,839 bytes for standard A-MSDU.

Question 5

Block Acknowledgment (Block ACK) in 802.11 allows a recipient to acknowledge multiple frames at once. What initiates a Block ACK session?

Accepted Answer

The transmitter sends an ADDBA (Add Block ACK) Request action frame

Answer

The transmitter initiates a Block ACK session by sending an ADDBA Request action frame; upon acceptance, the recipient sends an ADDBA Response.

CWS Exam Practice Test

CWS Exam Practice Test

CWS CWS MAC Layer Functions 4