PMKSA caching

4.10.6 PMKSA caching

The Authenticator and Supplicant may cache PMKSAs, which include the IEEE 802.1X state. A PMKSA
can be deleted from the cache for any reason and at any time.
The STA may supply a list of PMK or PSK key identifiers in the (Re)Association Request frame. Each key
identifier names a PMKSA; the PMKSA may contain a single PMK. The Authenticator specifies the
selected PMK or PSK key identifier in Message 1 of the 4-Way Handshake. The selection of the key
identifiers to be included within the (Re)Association Request frame and Message 1 of the 4-Way Handshake
is out of the scope of this standard.
4.10.7 Protection of group addressed robust management frames
When management frame protection is negotiated, all group addressed robust management frames are
encapsulated using the procedures defined in 10.13. This service provides integrity protection of group
addressed robust management frames using BIP.
4.11 Generic advertisement service (GAS)
GAS provides functionality that enables STAs to discover the availability of information related to desired
network services, e.g., information about services such as provided in an IBSS, local access services,
available subscription service providers (SSPs) and/or SSPNs or other external networks. GAS uses a
generic container to advertise network services' information over an IEEE 802.11 network. Public Action
frames are used to transport this information.
While the specification of network services information is outside the scope of this standard, in an
infrastructure BSS there is a need for STAs to query for information on network services provided by SSPNs
or other external networks beyond an AP, before they associate with the wireless LAN. The exchange of
information may also be performed after associating to the BSS.
In an IBSS GAS functionality enables a STA to access the availability and information related to desired
services provided by other STAs in the IBSS.
There are a number of reasons why providing information to a STA in a preassociated state is beneficial:
— It supports more informed decision making about an IEEE 802.11 infrastructure with which to
associate. This is generally more efficient than requiring a non-AP STA to associate with an AP
before discovering the information and then deciding whether to stay associated.
— It is possible for the non-AP STA to query multiple networks in parallel.
— The non-AP STA can discover information about APs that are not part of the same administrative
group as the AP with which it is associated, supporting the selection of an AP belonging to a
different IEEE 802.11 infrastructure that has an appropriate SSP roaming agreement in place.