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

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

    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.

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

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

    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.

  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)?

    Answer: Multi-User OFDMA with Trigger Frames

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

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

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

    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.

  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?

    Answer: Reduced Inter-Frame Space (RIFS)

    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.

  6. A client's 802.11 MAC header contains a ToDS=1 and FromDS=0. What does this indicate about the frame's direction?

    Answer: The frame is being sent from a client to the Distribution System through an AP (uplink)

    ToDS=1 and FromDS=0 means the frame is traveling from the STA to the AP and onward into the Distribution System — a standard uplink infrastructure mode frame.

  7. In 802.11 MAC, what is the purpose of the MPDU Delimiter in A-MPDU aggregation?

    Answer: It provides length and CRC fields so a receiver can identify and parse individual MPDUs within the aggregate

    Each MPDU in an A-MPDU is preceded by an MPDU Delimiter containing a length field and delimiter signature (0x4E), enabling the receiver to locate and independently decode each sub-frame.