802.11h Packet Formats
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).
Which frames are modified by 802.11h?
Beacon frames, Probe Response frames, and Action frames include new elements related to DFS and TPC.
What new information elements does 802.11h introduce?
It introduces Power Constraint, Channel Switch Announcement (CSA), and Extended Channel Switch Announcement elements.
What is the Power Constraint information element?
This element informs stations about transmit power limitations on certain channels to comply with regulatory limits.
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.
Are there any changes in data frame formats for 802.11h?
No, 802.11h mainly modifies management frames; data frames remain unchanged.
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.
How is the Power Constraint element formatted?
It consists of a single byte indicating the maximum allowed transmit power reduction in dB.
Do these new elements affect packet size?
Yes, they slightly increase the size of management frames but are necessary for regulatory compliance.
Are 802.11h packet formats backward compatible?
Yes, devices not supporting 802.11h simply ignore the additional information elements.
Which management frames commonly carry 802.11h elements?
Beacon frames, Probe Responses, Association Requests/Responses, and Action frames.
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.
How does the packet format support DFS?
By including CSA elements, devices inform clients about radar detection and upcoming channel moves.
Are action frames used in 802.11h packet formats?
Yes, action frames are used to trigger and confirm channel switch operations among associated devices.
How is the transmit power adjustment communicated in packets?
Power Constraint elements in beacons and probe responses inform stations of current transmit power limits.
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.
Can packet formats trigger immediate channel switches?
Yes, the CSA element can indicate immediate or timed channel switches based on radar detection.
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.
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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