 compatibility and interoperability of specifications broadband wireless products from different suppliers. Figure 4.1 Role of IEEE 802 and WiMAX forum with additional maintenance items and enhancements to the management information base specifications. Till the time of writing this chapter the IEEE 802.16-2009 standard was not publicly available. Thus, the details of air interface provided in this section are primarily based on IEEE 802.16-2004 and IEEE 802.16e-2005. All the current deployments of WiMAX are primarily based on either 802.16-2004 or 802.16e. The other current key 802.16 standards are as follows: IEEE 802.16k-2007 IEEE Standard for Media Access Control (MAC) Bridges Amendment 2: Bridging of IEEE 802.16. IEEE 802.16j-2009 Air Interface for Fixed and Mobile Broadband Wireless Access Systems - Multi-hop Relay Specification. This chapter focuses on the NLOS WiMAX systems that provide fixed and mobile broadband services. The chapter starts by providing details of WiMAX air interface standard (802.16 d/e) and advanced features of the radio technology. In the following sections the WiMAX network reference model, performance (both lab and field), certification process, forecast and roadmaps are explained. Air Interface The IEEE 802.16 reference model is shown in Figure 4.2 that illustrates the MAC (Media Access Control) and PHY (Physical) layers while keeping the network management aspects out of the specifications [1-3]. 4.2.1 MAC The MAC layer is designed to support a variety of applications in all the possible environments with the appropriate QoS requirements. It is based on the proven DOCSIS (Data Over Cable Service Interface Specifications) that defines standard interface for cable modems and supporting equipment. Though the MAC supports bandwidth allocation and QoS, the details of scheduling and reservation management are not listed in the standard. This gives an opportunity to vendors to achieve product differentiation and IEEE WiMAX Scope of standard CS SAP Management Entity Service-Specific Conve