• Hi Gene,

    The duration value of a non-fragmented data frame sets the NAV on stations to which the data frame is not intended. The purpose of this value is protection of the ACK frame that follows.

    I'm guessing your next question will be something like, "what's the point of that considering that the SIFS is higher priority than DIFS meaning the ACK will preempt any other frame?" The answer to this is that in 802.11, there is always BOTH a physical (interframe space) and virtual (duration value) protection of each frame with the exception of the first frame following the winning access to the medium (following a DIFS in DCF mode for example).


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