Friday, December 2, 2016

HT Capabilities Information Element

HT Capabilities information element contains fields that are used to advertise the optional capabilities of the HT station or HT AP. The HT Capabilities element is always present in the Beacon, Association Request, Association Response, Re-association Request, Re-association Response, Probe Request, and Probe Response frames of HT AP & HT stations.

Key Information from HT Capabilities IE:
  • AMPDU Parameters: Through this a HT node indicates its support for A-MPDU especially indicating the number of buffers dedicated to receive A-MPDU. Using this a receiver may also specify a minimum expected duration between MPDUs in an A-MPDU.
  • Supported MCS Set:  It indicates the MCSs supported by the station for transmit and receive.
  • HT Capabilities Info & HT Extended Capabilities: Both (each 16 bits) indicates the support for different HT capabilities of the node. The later was added for the expansion as the former bits were not sufficient. While the former is fully used the later has still many bits reserved for future use.

Key Capabilities indicated by HT Capabilities Info bits:
  • Supported Channel Width: Actual channel in use will be indicated by HT Information element.

  • Support for 11n Power Save Modes:

  • Support for Short GI

  • Enforcing not to do 40MHz transmission (intolerant)

  • Support for  Transmitting / Receiving STBC
  • AMSDU Length Information

Key Capabilities indicated by HT Extended Capabilities bits:

Where does the client indicates the antennas count it supports?

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