isms for secure exchange and distribution of authen- tication credentials and session keys for data encryption. The AAA protocols provide the following services: Authentication including device, user, or combined device and user authentication; Authorization including delivery of information to configure the session for access, mobility, QoS, and other applications; Accounting including delivery of billing information and other information that can be used to audit session activity by both the H-NSP and V-NSP. VIP Multimedia Subsystem (IMS) is an architectural framework for delivering IP multimedia services [4]. Vii A location-based service is a service provided to a subscriber based on the current geographic location of the MS. 2.3 Authentication, authorization, and accounting (AAA) Managed Service AAA Server/Proxy Connectivity IMS, LBS, MBS Mobile IP User Databases Subscriber Billing Router Support FIGURE 2-4 The CSN reference model The AAA framework supports global roaming across operator networks, including support for reuse of credentials and consistent use of authorization and accounting. It further supports roaming between H-NSP and V-NSP. The AAA framework is based on use of RADIUS or Diameter in ASN and CSN. The AAA framework accommodates both Mobile IPv4 [9] and Mobile IPv6 [10] Security Association (SA) management. It further accommodates various network operation scenarios from fixed to full mobility. The AAA framework provides support for deploying MS authorization, user and mutual authentication between MS and the NSP, based on Privacy Key Management (PKMv2). viii [18] In order to ensure interoperability, the AAA framework supports Extensible Authentication Protocol (EAP)-based authentication mechanisms that include passwords, Subscriber Identity Module [19], Universal Subscriber Identity Module [20], Universal Integrated Circuit Card [21], Removable User Identity Module [22], and X.509 digital certificates [23]. The AAA frame- work is capable of providing the V-CSN or ASN with a temporary identifie