802.11n MAC Timings
What are MAC timings in IEEE 802.11n?
MAC timings define intervals and durations for frame transmission, acknowledgments, and backoff to control medium access.
What is the Short Interframe Space (SIFS) in 802.11n?
SIFS is the shortest waiting time between frames, used for acknowledgments and high priority transmissions.
How does Distributed Interframe Space (DIFS) work?
DIFS is a waiting period before a station can contend for medium access after the channel is idle.
What is Arbitration Interframe Space (AIFS)?
AIFS varies per traffic category in QoS to provide prioritized medium access in 802.11n.
How does the backoff timer function in 802.11n MAC?
Stations pick a random backoff period within a contention window to reduce collisions before transmission.
What are contention windows (CWmin and CWmax)?
CWmin and CWmax define the minimum and maximum range for random backoff intervals during channel contention.
How is the contention window adjusted?
It doubles upon collisions (exponential backoff) until CWmax, then resets after successful transmissions.
What timing governs acknowledgement (ACK) frames?
ACK frames are sent after a SIFS interval following successful frame reception.
What is the role of Extended Interframe Space (EIFS)?
EIFS is a longer wait period after detecting erroneous frames, to avoid collisions during recovery.
How does MAC timing support frame aggregation in 802.11n?
Timings are adjusted to accommodate longer aggregated frames and reduce overhead between them.
What is the timing for Block Acknowledgment (BA)?
BAs are sent after a SIFS interval to acknowledge multiple frames in one response.
How does MAC timing affect QoS in 802.11n?
Different traffic classes use varied AIFS and contention windows to prioritize access.
What is slot time in 802.11n?
Slot time is the basic unit of backoff and timing, typically 9 microseconds for 802.11n in 5 GHz.
Why is timing synchronization important in MAC?
It ensures coordinated transmissions, prevents collisions, and maintains fairness in medium access.
How are MAC timings affected by different PHY rates?
Higher PHY rates may reduce frame durations but MAC timing intervals like SIFS remain constant.
What timing mechanisms prevent hidden node collisions?
RTS/CTS handshake timings help reserve the medium and avoid collisions from hidden nodes.
How do MAC timings interact with power save modes?
Stations use timing parameters to wake up and listen for buffered frames signaled in beacon intervals.
What happens if timing intervals are not respected?
Violations can cause collisions, reduced throughput, and increased retransmissions.
How does the MAC timing adapt in dense networks?
Contention windows may increase to reduce collisions, and QoS timings help prioritize critical traffic.
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