WIFI连接建立过程
WIFI建立过程概述：
STA ------------> Probe Request ----------------> AP //广播自身数据
STA <------------ Probe Response <------------- AP
STA ------------> Authentication Request --------> AP //认证Auth类型，Open System , Shared Key等
STA ------------> Authentication Response------> AP
STA-------------> Association Request ------------> AP //请求与AP建立关联，从而可以进行数据交互
STA-------------> Association Response-----------> AP
WEP/WPA/WPA2/DISABLED Security Type.
Data Communication
http://standards.ieee.org/about/get/802/802.11.html
