Station Services
The 802.11 standard defines services for providing functions among stations. A station may be within any wireless element on the network, such as a handheld PC or handheld scanner. In addition, all access points implement station services. To provide necessary functionality, these stations need to send and receive MSDUs and implement adequate levels of security.
Authentication
Because wireless LANs have limited physical security to prevent unauthorized access, 802.11 defines authentication services to control LAN access to a level equal to a wired link. Every 802.11 station, whether part of an independent BSS or an ESS network, must use the authentication service prior to establishing a connection (referred to as an association in 802.11 terms) with another station with which it will communicate. Stations performing authentication send a unicast management authentication frame to the corresponding station.
The IEEE 802.11 standard defines the following two authentication services:
Open system authentication This is the 802.11 default authentication method. It is a very simple two-step process. First the station wanting to authenticate with another station sends an authentication management frame containing the sending station's identity. The receiving station then sends back a frame indicating whether it recognizes the identity of the authenticating station.
Shared key authentication This type of authentication assumes that each station has received a secret shared key through a secure channel independent from the 802.11 network. Stations authenticate through shared knowledge of the secret key. Use of shared key authentication requires implementation of the Wired Equivalent Privacy algorithm (WEP).
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