EAP-MSK & WiMAX-MSK validity?

Hi All, i use: - WiMAX-MSK = EAP-MSK and all it works correctly, and I suppose It's validity is only for the authentication session, it is right? - WiMAX-AAA-Session-Id: is set as a pseudo-random value. It's correct? It's value is related to the duration of the session? Thanks all in advance! Stefano