In 802.11, which has the longest interval between frames?

Question

Options

• ASIFS
• BIFS
• CDIFS
• DPIFS

• A
  6% (3)
• B
  2% (1)
• C
  78% (40)
• D
  14% (7)

Explanation

DIFS (Distributed Coordination Function Interframe Space) is the longest interval among the defined IFS types in 802.11, used before stations attempt to transmit regular data frames under the DCF access method. The longer wait ensures that high-priority traffic gets through first by giving ACKs and other control frames a head start.

SIFS (Short Interframe Space) is intentionally the shortest interval, reserved for the highest-priority responses like ACKs and CTS frames, so those replies preempt any new transmissions. PIFS (Point Coordination Function IFS) falls between SIFS and DIFS, used by the access point in PCF mode to gain priority over normal stations without being as urgent as a SIFS response. Option B, "IFS," is simply the generic category name (Interframe Space) and does not refer to any specific defined interval with a measurable duration.

Memory tip: Rank the intervals by priority in reverse - the most urgent frame types (ACKs) get the shortest wait (SIFS), the access point gets a medium wait (PIFS), and ordinary stations competing for the channel wait the longest (DIFS). Shortest wait = highest priority.

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