802.11h Packet Formats
==========================


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        **What is unique about packet formats in 802.11h?**

        802.11h extends standard 802.11 management frames by including additional information elements for Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC).

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        **Which frames are modified by 802.11h?**

        Beacon frames, Probe Response frames, and Action frames include new elements related to DFS and TPC.

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        **What new information elements does 802.11h introduce?**

        It introduces Power Constraint, Channel Switch Announcement (CSA), and Extended Channel Switch Announcement elements.

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        **What is the Power Constraint information element?**

        This element informs stations about transmit power limitations on certain channels to comply with regulatory limits.

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        **How does the Channel Switch Announcement element work in packet formats?**

        CSA is included in management frames to notify clients of upcoming channel changes due to radar detection or other reasons.

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        **Are there any changes in data frame formats for 802.11h?**

        No, 802.11h mainly modifies management frames; data frames remain unchanged.

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        **What is the format of the Channel Switch Announcement element?**

        It contains fields specifying the new channel number and the countdown for when the switch will occur.

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        **How is the Power Constraint element formatted?**

        It consists of a single byte indicating the maximum allowed transmit power reduction in dB.

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        **Do these new elements affect packet size?**

        Yes, they slightly increase the size of management frames but are necessary for regulatory compliance.

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        **Are 802.11h packet formats backward compatible?**

        Yes, devices not supporting 802.11h simply ignore the additional information elements.

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        **Which management frames commonly carry 802.11h elements?**

        Beacon frames, Probe Responses, Association Requests/Responses, and Action frames.

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        **What is the purpose of the Extended Channel Switch Announcement?**

        It supports more complex channel switching scenarios, such as switching multiple channels or bandwidth adjustments.

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        **How does the packet format support DFS?**

        By including CSA elements, devices inform clients about radar detection and upcoming channel moves.

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        **Are action frames used in 802.11h packet formats?**

        Yes, action frames are used to trigger and confirm channel switch operations among associated devices.

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        **How is the transmit power adjustment communicated in packets?**

        Power Constraint elements in beacons and probe responses inform stations of current transmit power limits.

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        **Do 802.11h packet formats vary by regulatory domain?**

        The elements are standard, but the values within them (e.g., power constraints) vary by region.

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        **Can packet formats trigger immediate channel switches?**

        Yes, the CSA element can indicate immediate or timed channel switches based on radar detection.

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        **How do client devices recognize 802.11h-specific elements?**

        Clients parse the information element IDs in management frames and act accordingly if they support 802.11h.

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        **Are vendor-specific extensions common in 802.11h packet formats?**

        Some vendors may add proprietary elements, but these are separate from the standard 802.11h elements.


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        Topics in this section,

                * :ref:`Reference links <packet_formats_80211h_step17>`


.. _packet_formats_80211h_step17:

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    .. tab-item:: Reference links
     
       * Reference links