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CWS MAC Layer Functions Flashcards

7 cards from real CWS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 CWS MAC Layer Functions flashcards as text

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

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

    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.

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

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

    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.

  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?

    Answer: A-MPDU

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

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

    Answer: 7,935 bytes

    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.

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

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

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

  6. Which 802.11 MAC feature allows a transmitter to fragment large MSDUs into smaller MPDUs to improve reliability in noisy environments?

    Answer: MSDU fragmentation

    Fragmentation splits a large MSDU into multiple smaller MPDUs, each sent with its own ACK, reducing the probability that noise causes a complete retransmission of a large frame.

  7. In 802.11 MAC, what field in the frame header is used to reserve the channel medium for a specified duration during an RTS/CTS exchange?

    Answer: Duration/ID field

    The Duration/ID field in both RTS and CTS frames specifies the time (in microseconds) the medium must be reserved, causing neighboring stations to update their NAV (Network Allocation Vector).