
WiMAX: Worldwide Interoperability for Microwave Access ◾ 63
Message 1: BS → SS:SeqNo||SAID||HMAC(1)
Computation of HMAC (1) is used by the SS to detect forgeries in the network.
Message 2 is issued by the SS to request SA parameters:
Message 2: SS → BS:SeqNo||SAID||HMAC(2)
For this message, the SS takes its SAID from the authorization protocol SAIDList.
Separate Message 2 is used for different SAs. By computing HMAC (2), the BS can
detect forgeries in the network. A valid HMAC (2) authenticates SS to BS.
If HMAC (2) is valid and SAID identifies one of the SS’s SA, then the BS uses
Message 3 to create and configure an SA:Message 3: BS → SS:SeqNo||