802.11e PHYs
==============

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        **What is IEEE 802.11e?**

        IEEE 802.11e is an amendment to IEEE 802.11 that introduces enhancements for Quality of Service (QoS) at the MAC layer. :contentReference[oaicite:0]{index=0}

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        **Does 802.11e change the physical layer (PHY) modulation or channel parameters?**

        No. 802.11e does *not* alter modulation schemes or channel widths defined by the underlying PHY standards (such as 802.11a/b/g); it works above the PHY. :contentReference[oaicite:1]{index=1}

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        **What is EDCA in 802.11e?**

        EDCA (Enhanced Distributed Channel Access) is a mechanism in 802.11e that provides prioritized access to the channel by defining different access categories (ACs) like Voice, Video, Best Effort, and Background. :contentReference[oaicite:2]{index=2}

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        **What are Access Categories (ACs)?**

        In EDCA, traffic is classified into ACs (Voice, Video, Best Effort, Background), each with different channel access parameters (like smaller backoff windows or shorter wait times) to give priority to more time‑sensitive traffic. :contentReference[oaicite:3]{index=3}

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        **What is HCF in 802.11e?**

        HCF (Hybrid Coordination Function) combines both EDCA and a controlled access method (HCCA) to provide QoS. :contentReference[oaicite:4]{index=4}

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        **What is HCCA (HCF Controlled Channel Access)?**

        HCCA is a polling‑based channel access method under HCF for delivering traffic with QoS guarantees (e.g., delay). It requires a coordinator to manage who transmits when. :contentReference[oaicite:5]{index=5}

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        **How does 802.11e affect latency and jitter for voice/video traffic?**

        By giving higher priority ACs smaller contention windows, shorter wait intervals, and possibly larger TXOPs, 802.11e reduces latency and jitter for voice/video compared to best‑effort traffic. :contentReference[oaicite:6]{index=6}

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        **What is TXOP (Transmission Opportunity)?**

        TXOP defines a time duration during which a station may transmit multiple frames once it gains access to the channel. Higher priority ACs may be given longer TXOPs. :contentReference[oaicite:7]{index=7}

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        **What is Arbitration Inter Frame Space (AIFS)?**

        AIFS is the waiting period a station waits after the channel is idle before beginning its backoff. It varies per access category: high priority ACs have shorter AIFS. :contentReference[oaicite:8]{index=8}

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        **What is Contention Window (CW) in 802.11e?**

        It’s the range from which a random backoff interval is chosen. High priority ACs have smaller CWmin/CWmax so they tend to get the channel sooner. :contentReference[oaicite:9]{index=9}

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        **What is a QoS‑Enabled Station (QSTA)?**

        A QSTA is a station (client) that supports the QoS features of 802.11e (e.g. EDCA / HCCA). :contentReference[oaicite:10]{index=10}

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        **What is a QoS‑Enabled Access Point (QAP)?**

        A QAP is an AP that supports 802.11e functions and acts as coordinator for QoS, possibly managing HCCA or configuring EDCA parameters. :contentReference[oaicite:11]{index=11}

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        **Does 802.11e guarantee throughput?**

        Not strictly. It gives priority, but for strict guarantees (bandwidth / delay), HCCA is needed. EDCA can improve QoS but isn’t deterministic. :contentReference[oaicite:12]{index=12}

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        **How does 802.11e relate to older standards like 802.11a/b/g?**

        It builds on them: channel definitions, modulation etc. come from PHYs of those standards; 802.11e adds QoS at MAC but doesn’t change the PHY. :contentReference[oaicite:13]{index=13}


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        Topics in this section,

                * :ref:`Reference links <phy_e_step17>`


.. _phy_e_step17:

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    .. tab-item:: Reference links

       * Reference links