Friday, December 2, 2016

HT Information Element

The HT Information element contains operational parameters and hence dynamically controls the behavior of HT STAs in the BSS. Some fields in the HT Information element change dynamically with changes in the BSS.

To control the operation of stations on a BSS, the AP uses the HT Information element in Beacon, Probe Response, Association Response, and Reassociation Response frames. It is used only by AP not stations.

The AP also provides information on the capabilities of stations that are members of the BSS or, optionally, detected operating in the same channel(s). This enables protection for certain HT sequences a station may use but for which nearby station may not correctly defer.

Key Information provided by HT IE:

  • AP operating Channel & Channel Width allowed for Stations

  • RIFS Mode: Indicates whether or not RIFS is permitted with in the BSS. For example, the association of a legacy station would require the AP prohibit the use of RIFS.
  • MCS values supported by all HT STAs in BSS

  • STBC Parameters
  • HT Protection

  • Others:

  • Non-Greenfield HT STAs Present:This indicates that there are HT stations associated with the BSS or in neighboring BSSs that are unable to receive HT Greenfield format PPDUs. When set, stations must protect HT Greenfield format transmissions.
  • OBSS Non-HT STAs Present: This indicates that there may be non-HT stations present that are not members of the BSS. Astationmay optionally use this to determine if protection is necessary for HT sequences.
  • RIFS Mode: The AP can directly control whether or not RIFS bursting is permitted through the RIFS Mode bit. Stations may only use RIFS bursting when this bit is set to 1.

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