NAS Authentication
Typically agent for PPP authentication (PAP, CHAP, MS-CHAP, EAP)
Transmits this information securely to a server
Server typically resolves this information at a user database (Unix NIS, NT Domain, NDS, LDAP) or Other authentication type (SecureID, etc)
Or proxy to another server or realm (eg: roaming, see RoamOps WG)