802.11e MAC Functions
What are MAC functions in IEEE 802.11e?
MAC functions in 802.11e extend the traditional MAC layer to support Quality of Service (QoS) in wireless networks.
What is the main enhancement of 802.11e MAC over 802.11a/b/g?
802.11e introduces QoS enhancements such as traffic prioritization and scheduling mechanisms like EDCA and HCCA.
What is EDCA in the context of MAC functions?
EDCA (Enhanced Distributed Channel Access) provides differentiated access to the wireless medium for different traffic types.
How does HCCA work in IEEE 802.11e?
HCCA (HCF Controlled Channel Access) allows centralized scheduling of traffic using a Hybrid Coordinator in the access point.
How are access categories defined in 802.11e MAC?
802.11e defines four Access Categories: Voice (AC_VO), Video (AC_VI), Best Effort (AC_BE), and Background (AC_BK).
Does 802.11e support legacy MAC functions?
Yes, it retains standard MAC functions such as CSMA/CA, ACKs, retransmissions, and fragmentation while adding QoS.
What is the Hybrid Coordination Function (HCF)?
HCF is the central QoS coordination method in 802.11e that includes both EDCA and HCCA mechanisms.
How does the MAC layer manage QoS traffic in 802.11e?
It uses traffic identifiers (TIDs) and access categories (ACs) to classify and prioritize packets.
What is the function of AIFS in 802.11e MAC?
AIFS (Arbitration Interframe Space) replaces DIFS and provides different interframe spaces for different traffic categories.
How does the MAC layer support delay-sensitive applications?
Through shorter contention windows and prioritized access categories, 802.11e supports low-latency transmissions.
Does 802.11e introduce new frame types?
No, but it adds QoS Control fields to existing MAC frame structures for enhanced traffic classification.
How does 802.11e ensure reliable delivery with QoS?
It maintains ACK, retransmission, and sequence control mechanisms while prioritizing higher-class traffic.
What is a TXOP (Transmission Opportunity)?
TXOP is a bounded time period in which a station can send multiple frames without recontending for the channel.
How does the MAC layer manage collisions in 802.11e?
It uses CSMA/CA with differentiated contention windows for each access category to reduce collision probability.
How are voice and video prioritized at the MAC layer?
By assigning them to AC_VO and AC_VI, which have lower contention window sizes and shorter AIFS.
Is 802.11e MAC compatible with non-QoS devices?
Yes, it can fall back to legacy behavior when communicating with devices that do not support QoS.
What is the role of QoS Control field in 802.11e MAC frames?
It carries information like TID, ACK policy, and TXOP duration to enable fine-grained QoS control.
Does 802.11e MAC improve throughput?
Yes, by enabling prioritization and reducing contention delays for time-sensitive traffic, it improves overall efficiency.
What is the function of backoff in 802.11e MAC?
Backoff is used to manage contention; 802.11e uses separate backoff counters for each access category.
How does 802.11e handle legacy MAC queues?
It maps legacy traffic to Best Effort (AC_BE) queue, ensuring backward compatibility while supporting QoS for enhanced traffic.
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