802.11e MAC Timings
What are MAC timings in IEEE 802.11e?
MAC timings in 802.11e define interframe spaces, backoff mechanisms, and timing rules to support QoS and efficient channel access.
What new timing element does 802.11e introduce?
802.11e introduces Arbitration Interframe Space (AIFS) to provide differentiated access delays for various traffic classes.
How does AIFS differ from DIFS?
AIFS replaces DIFS in 802.11e and allows different interframe space durations based on traffic priority levels.
What is TXOP in 802.11e timing?
TXOP (Transmission Opportunity) is a defined time interval during which a station can transmit multiple frames without contention.
How does TXOP improve efficiency?
TXOP reduces the number of contention events by allowing a station to transmit a burst of data in one go.
How is backoff handled in 802.11e?
Each access category maintains its own backoff timer, allowing prioritization of traffic through varied contention windows.
What is the role of SIFS in 802.11e?
SIFS (Short Interframe Space) remains the shortest interframe delay and is used for immediate responses like ACKs and CTS.
What does the EDCA mechanism use for timing?
EDCA uses AIFS, CWmin, CWmax, and TXOP values to manage medium access for different traffic types.
How does HCCA manage timing?
In HCCA, the Hybrid Coordinator centrally schedules transmission times for stations, reducing contention delays.
What timing parameter replaces DIFS in 802.11e?
Arbitration Interframe Space (AIFS) replaces DIFS in Enhanced Distributed Channel Access (EDCA).
What determines AIFS value for a station?
AIFS is calculated as AIFSN[AC] × slot time + SIFS, where AIFSN depends on the Access Category.
How are interframe spaces prioritized?
Shorter AIFS values are assigned to higher-priority traffic like voice and video.
Do 802.11e timing parameters affect latency?
Yes, shorter AIFS and smaller contention windows for higher-priority traffic reduce transmission latency.
Is backoff timer resetting different in 802.11e?
No, backoff timers operate similarly but are managed independently for each access category to avoid internal collisions.
How is fairness maintained in 802.11e timing?
By using separate queues and timers per access category, while adjusting contention windows to balance access opportunities.
Can TXOP durations vary across traffic classes?
Yes, TXOP durations are configurable and typically longer for high-bandwidth traffic such as video.
Are legacy devices affected by 802.11e timings?
Legacy devices use DIFS and standard backoff; they can still coexist with 802.11e devices through backward compatibility.
What is the benefit of separate queues in timing?
Separate queues prevent lower-priority traffic from blocking higher-priority frames, reducing delay and jitter.
What happens when two access categories within a device collide?
The higher-priority category wins, and the lower-priority one follows a virtual collision handling routine.
How do MAC timings support real-time applications in 802.11e?
Through shorter interframe spaces and prioritized TXOPs, 802.11e reduces delays and jitter for voice/video traffic.
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