Proactive Key Caching(PKC)

PKC is an IEEE 802.11i extension that allows for the proactive caching (before the client roaming event) of the WPA/WPA2 PMK that is derived during a client IEEE 802.1 x/EAP authentication at the AP. If a PMK (for a given WLAN client) is already present at an AP when presented by the associating client, full IEEE 802.1X/EAP authentication is not required. Instead, the WLAN client can simply use the WPA 4-way handshake process to securely derive a new session encryption key for communication with that AP.

Note PKC is an IEEE 802.11i extension and so is supported in WPA2—not WPA.