 payloads that are natively carried over the intermediate networks. Tunneling is alternately referred to as encapsulation. CHAPTER 2 WiMAX Network Architecture Reference Point R8 Reference point R8 within an ASN consists of a set of control messages exchanged between the base stations to ensure fast and seamless handover. The control-plane consists of the inter-BS communi- cation protocol consistent with the IEEE 802.16-2009 standard [12] and mobile WiMAX system profile [11], as well as additional protocols for data forwarding between base stations. 2.2.4 Connectivity Service Network (CSN) Connectivity Service Network is defined as a set of network functions that provide IP connectivity to user terminals. A CSN can provide the following functions [5,13-15]: MS IP address and endpoint parameter allocation for user sessions; Internet access; AAA proxy/server; Policy and admission control based on user profiles; ASN-CSN tunneling support; Subscriber billing; Inter-CSN tunneling for roaming; Inter-ASN mobility management and mobile IP home agent functionality; Network services such as connectivity for peer-to-peer services, provisioning, authorization and/or connectivity to IP multimedia services, and to enable lawful interception; Connectivity to Internet and managed services such as IP Multimedia Subsystem (IMS), Location-Based Services (LBS), vii Multicast and Broadcast Services (MBS), etc.; Over-the-air activation and provisioning of mobile WiMAX terminals. The CSN may further comprise network elements such as routers, AAA proxy/servers, user databases, and interworking functions. The CSN reference model is depicted Figure 2-4. 2.3 AUTHENTICATION, AUTHORIZATION, AND ACCOUNTING (AAA) AAA refers to a framework based on IETF protocols, Remote Authentication Dial-in User Service (RADIUS) [16] or Diameter [17], which specify the procedures for authentication, authorization, and accounting associated with the user terminal's subscribed services across different access technol- logies. As an example, AAA includes mechan