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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.

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  1. What is the primary purpose of the Distributed Coordination Function (DCF) in 802.11 MAC?

    Answer: To provide contention-based channel access using CSMA/CA

    DCF is the fundamental 802.11 MAC access method, using CSMA/CA so stations contend for the channel rather than being assigned fixed slots.

  2. In 802.11 CSMA/CA, a station must sense the medium idle for a DIFS period before transmitting. What does DIFS stand for?

    Answer: Distributed Inter-Frame Space

    DIFS (Distributed Inter-Frame Space) is the mandatory idle time a station must observe before initiating a new transmission under DCF.

  3. After detecting the channel is busy, a station invoking binary exponential backoff selects a random number from the contention window. What happens to the contention window size after each successive collision?

    Answer: It doubles up to a defined maximum

    Binary exponential backoff doubles the contention window after each collision, up to a maximum CW value, to reduce the probability of repeated collisions.

  4. Which inter-frame space is the SHORTEST and is used to give priority to ACK and CTS frames?

    Answer: SIFS

    SIFS (Short Inter-Frame Space) is the shortest IFS and is used for high-priority responses like ACKs and CTS frames, preventing other stations from interrupting an exchange.

  5. A station completes a successful data frame exchange. According to DCF, what must happen before the receiving station sends an ACK?

    Answer: Wait a SIFS period

    After receiving a unicast data frame, the recipient waits a SIFS before transmitting the ACK, ensuring the ACK gets channel priority over new transmissions.

  6. What mechanism does 802.11 MAC use to detect and discard duplicate frames caused by retransmissions?

    Answer: The Sequence Control field and the Retry bit in the MAC header

    Receiving stations track the Sequence Control field and examine the Retry bit to identify and discard frames that are retransmissions of already-received frames.

  7. Which MAC frame type is responsible for managing 802.11 association and authentication between a client and an AP?

    Answer: Management frames

    Management frames handle high-level operations like authentication, association, deauthentication, and probe requests/responses between STAs and APs.