When establishing a connection from a WLAN client to an access point operating with 802.1x-authentication, the two stations negotiate a shared key, known as the Pairwise Master Key (PMK), for the subsequent encryption. In applications with mobile WLAN clients (laptops in large offices, moving objects with WLAN connections in the industrial sector), the WLAN clients often change the access points via which they are logged in to the WLAN network. And although WLAN clients roam back and forth between different access points, in most cases these tend to be the same ones.
Access points typically save a negotiated PMK for a certain period of time. WLAN devices in WLAN client mode also store PMKs. As soon as a WLAN client starts a login procedure for which a connection already existed, the WLAN client can directly transfer the existing PMK to the access point. In this way, the two remote stations skip the PMK negotiation phase while establishing the connection, and the WLAN client and access point establish the connection much faster.
