802.11ag MAC Timings
What are MAC timing parameters in IEEE 802.11a/g?
MAC timing parameters define intervals and durations used for coordinating frame transmissions and medium access.
What is the Short Interframe Space (SIFS)?
SIFS is the shortest waiting period between frames, used for high-priority control frames like ACKs and CTS.
What is the Distributed Interframe Space (DIFS)?
DIFS is the time a device waits after the medium is idle before attempting a new data transmission.
How long is SIFS in 802.11a/g?
In 802.11a and 802.11g, SIFS is typically 16 microseconds.
How long is DIFS in 802.11a/g?
DIFS is calculated as SIFS plus two slot times, typically 34 microseconds in 802.11a/g.
What is a slot time?
Slot time is the basic time unit used for backoff intervals and timing calculations in the MAC layer.
What is the slot time duration in 802.11a/g?
The slot time is 9 microseconds for both 802.11a and 802.11g.
What is Extended Interframe Space (EIFS)?
EIFS is a longer waiting period used when a frame with errors is detected, allowing recovery time before retransmission.
How is EIFS calculated?
EIFS = Transmission time of ACK + SIFS + DIFS, typically longer than DIFS to prevent collisions after errors.
What is the purpose of interframe spaces in MAC timings?
They prioritize access to the medium by spacing transmissions to avoid collisions and allow important control frames timely access.
How does the MAC layer use timing for collision avoidance?
Devices defer transmissions by waiting for DIFS and a random backoff period to reduce simultaneous access attempts.
What role does timing play in ACK frame transmission?
The receiver must send an ACK after SIFS to acknowledge successful frame reception promptly.
How is the backoff timer calculated?
The backoff timer is a random number of slot times chosen from the contention window, multiplied by the slot duration.
What is the minimum contention window size in 802.11a/g?
The minimum contention window (CWmin) is 15 slots, doubling with each retransmission up to a maximum.
What is the maximum contention window size?
The maximum contention window (CWmax) is 1023 slots in 802.11a/g, used after multiple retries.
How do timing parameters affect throughput?
Shorter interframe spaces and slot times improve throughput but may increase collision risk.
Can MAC timing parameters be adjusted?
Some devices allow limited tuning of parameters like contention windows for performance optimization.
How do timing parameters differ between 802.11a and 802.11b?
802.11a has shorter slot times (9 µs) compared to 802.11b (20 µs), enabling faster medium access.
Why is timing synchronization important in MAC?
Synchronization ensures all devices use the same timing rules to coordinate access and avoid collisions.
How do access points use timing to coordinate the network?
Access points send beacon frames at regular intervals to synchronize device clocks and timing parameters.
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