If the 802.11 authentication phase completes with a Success result, the station movies to the association phase. The purpose of this exchange is for the station to join the cell and obtain a cell member identifier (AID). The association frame is a unicast management frame and is always acknowledged.
The following picture and table show the frame format and elements for the association request.
above pictures from CWAP
wlan.fc.type_subtype == 0x0000
After association request, AP will sent association response to the client. The following picture and table show the frame format and elements for the association response.
above pictures from CWAP
If AP returns the association response frame as Status Code = Successful, the AP communicates an association ID, which is the station identifier on the access point. The AID value is an integer between 1 and 2007. Although the field is 2 bytes long, only the 14 less significant bits are used (the others are set to 1). In reality, you would probably never see 2,007 stations associated to a single AP.
The overhead required to maintain the cell state with so many stations would create so
many collisions that the associations could never reach this number.
wlan.fc.type_subtype == 0x0001
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