Each AK has an expiration time before which SS is reauthenticated
and reauthorized. Along with the authorization, the SS is also issued the identities
and properties of the Security Associations that the SS is authorized to obtain.
Security Association IEEE 802.16 standard uses the notion of a Security Association (SA)
which defines a set of security information shared between a BS and one or more SSs
in order to support secure transfers of data between these devices. Each SA defines a
Cryptographic Suite used for the SA. The SA may also contain the encryption key and
other parameters associated with the Cryptographic Suite.
There are three types of SA defined by the standard. Primary SA is an SA established
by a SS during its initialization into the network. The Primary SA established by an SS
is shared between the SS and the BA only. Static SAs are created by the BS based on
provisioning. Dynamic SAs are established and torn down as service flows are created
and eliminated. Dynamic and Static SAs can be shared among multiple SSs (e.g., for
multicast traffic). The cryptographic suite and keys associated with each service flow
is used to secure the service flow data.
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