Understanding the 802.11 Association Request and Response Frames

 When your smartphone or laptop (known as a STA - Station) connects to a WiFi access point (AP), it goes through a sequence of steps. This process ensures both devices can communicate effectively and securely. After successful open Authentication Phase, the Station goes through the Association Phase

Association Request

The Station device sends an Association Request frame to the SSID it is interested to connect with containing following information:

  • Capability Information: What your device can do
  • Listen Interval: How often it will wake up to check for messages. It is measured in the units of Beacon Interval 
  • Network Name (SSID): The WiFi network it wants to join
  • Supported Rates: What data rates station can handle
If the capabilities match those of the Access Point the STA is connecting to, the STA will become associated to the Access Point and be the part of the BSS.

Following Capture shows parameters of Association Request:



Association Response

Upon receiving Association Request, The access point responds with an Association Response frame that include following information:
  • Capability Information: What features are available
  • Status Code: Whether the association was successful 
  • Association ID (AID): A unique identifier for the station which is used for the power save mode
  • Supported Rates: What data rates AP supports 

Following Capture shows parameters of Association Response :


Conclusion:

Though these frames sound very basic and fundamental, the negotiation that happen in this phase is very crucial for establishing a reliable communication link before data transmission begins. Further the Association ID and Listen Interval plays an important role for the devices in Power Save Mode as it tells the access point how often a device in power save mode will wake up to listen for beacon frames. Mobility Domain and Fast BSS Transition are used when Stations are performing FT roaming. 


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