IEEE 802.16 standards family designed the physical and the MAC layers to provide broadband services access at the metropolitan scale for fixed, nomadic, portable, and mobile subscribers. The WiAMX forum, whose mission is to promote the interoperability of the broadband wireless access equipments implementing the IEEE 802.16 and ETSI HIPERMAN standards, has created a Network Working Group and a Service Provider Working Group to address higher-layer specifications such as intervendor inter-network interoperability for roaming, multivendor access networks, and intercompany billing. The result of these standardization efforts is the mobile WiMAX end-to-end architecture. The architecture is based on an all-IP platform implementing packet switching; it defines an access network and a common core network while decoupling the access from connectivity IP service. Moreover, the end-to-end architecture is designed to support loosely coupled interworking with existing wireless networks such as UMTS and existing wired networks such as DSL. Besides, a global roaming across WiAMX operator networks is achieved through the support for credential reuse, common billing and settlement, and consistent use of authentication, authorization, and accounting (AAA) services. The WiMAX forum designed the WiMAX network reference model (NRM), which aims at achieving interoperability through identifying the functional entities and reference points and the corresponding communication protocols and data plane treatment within a logical representation of the network architecture. As depicted in Figure 1, the MS, the access service network (ASN), and the connectivity service network (CSN) represent a set of functional entities that may be implemented by a single physical device or by different physical devices. The ASN is formed by at least one BS and one ASN gateway (ASN GW); it implements the access services and represents a boundary for functional interoperability with WiMAX clients and WiAMX connectivity service functions. For instance, the BS manages the MSs in its coverage while the ASN GW relays data to the CSN. On the other hand, the CSN may be defined as a network of Internet gateways, user databases, routers, servers, and proxies providing IP connectivity services to WiMAX subscribers.
Figure 1: The WiMAX NRM.
Mobile WiMAX end-to-end architecture is based on a security framework which provides basic security services and particularly authentication and confidentiality. In fact, each MS authenticates itself to the WiMAX network while the WiMAX network authenticates itself to the MS by implementing consistent and extensible authentication mechanisms. Besides, data confidentiality and integrity, replay protection and nonrepudiation services are guaranteed using applicable key length. Last but not least, MSs have the possibility to initiate and terminate specific security mechanisms such as virtual private networks (VPNs). The end-to-end architecture supports advanced IPv4-or IPv6-based mobility management mechanisms. For instance, vertical handovers can occur with wireless LANs or third generation wireless networks while roaming between different network service providers (NSPs) is supported. Seamless handover is also supported at up to vehicular speed while optimizing the overall network resources through the implementation of dynamic and static home address configurations, dynamic assignment of the home agent in the service provider network, and in the home IP network based on policies, etc. WiMAX mobility management will be further detailed.
