Open System Authentication (OSA): In OSA mechanism, first, the computer sends a request for authentication to the access point. Then the access point generates an authentication code (for use only during that session). Finally, the computer accepts the authentication code and becomes part of the network as long as the session continues and the computer remains within range of the original access point.
Shared Key Authentication (SKA): It pre-establishes that a requesting system has knowledge of a shared secret key required for authentication. For exchange encrypted data between a WEP network access point and a wireless-equipped computer, SKA is required, because SKA is stronger than OSA in encryption.
Temporal Key Integrity Protocol (TKIP): It combines a secret root key with the initialization vector by using a key-mixing function. TKIP is based on the RC4 cipher, rather than the (assumed) more secure AES. The key used for encryption in TKIP is 128 bits long. WPA that uses TKIP is considered unreliable still.
Extensible Authentication Protocol (EAP): It is an authentication framework. The EAP protocol can support multiple authentication mechanisms. EAP runs directly over the link layer without requiring IP.
EAP is a lock step protocol which only supports a single packet in at a time. As a result, it cannot efficiently transport bulk data.