ent schemes based on open, broadly deployable, industry standards. Over-the-Air (OTA) services for MS provisioning and software upgrades are accommodated. The network protocols accommodate use of header compression/suppression and/or payload compression for efficient use of WiMAX radio resources. The architecture supports mechanisms that enable maximum possible enforcement and fast re-establishment of established QoS SLAs due to handover impairments. The WiMAX network supports interoperability between equipment from different manufacturers within an ASN and across ASNs. Such interoperability includes interoperability between BS and backhaul equipment within an ASN, interoperability between various ASN elements (possibly from different vendors) and CSN, with minimal or no degradation in functionality or capability of the ASN. The IEEE 802.16-2009 standard defines multiple convergence sub-layers. The network architec- ture further supports the following convergence sub-layer (CS) types: Ethernet CS and IPv4/IPv6 over Ethernet CS; IPv4 CS; and IPv6 CS. 2.2 NETWORK REFERENCE MODEL The Network Reference Model is a logical representation of the network architecture. The NRM identifies functional entities and reference points over which interoperability is achieved. Figure 2-1 illustrates the WiMAX NRM, consisting of the following logical entities: mobile station (MS); ASN; and CSN, which are described in the following sections. The interfaces R1-R8 are normative reference points [5]. Each of the entities MS, ASN, and CSN represent a group of functions. Each of these functions can be realized in a single physical entity or may be distributed over multiple physical entities. The reference model is used to ensure interoperability among different implementations of functional entities in the network. Interoperability is verified based on the definition of logical interfaces in order to achieve an end-to-end functionality, e.g., security or mobility management. Thus, the functional entities on either side of a reference poi