R/IMT-Advanced for 4G systems, as well as the next generation mobile network operators. Depending on the available bandwidth and multi-antenna mode, IEEE 802.16m systems will be capable of over-the-air data transfer rates in excess of 1 Gbit/sec and support of a wide range of high-quality and high-capacity IP-based services and applications while maintaining full backward compatibility with the existing mobile WiMAX systems (to preserve investments and continuing support for the first generation products). The IEEE 802.1 16m will be suitable for both green-field and mixed deployments with legacy mobile stations and base stations. The backward compatibility feature would allow upgrades and evolution paths for existing deployments. It will enable roaming and seamless connectivity across IMT-Advanced and IMT-2000 systems through the use of appropriate interworking functions. The IEEE 802.16 systems further utilize multi-hop relay architectures for improved coverage and performance. 1.3 INTRODUCTION TO WiMAX FORUM MOBILE SYSTEM PROFILES The IEEE 802 standards only define the physical and medium access control layers (i.e., Layers 1 and 2 of the OSI reference model). This approach has worked well for technologies such as Ethernet and Wi-Fi, relying on other bodies such as the IETF to set the standards for higher layer protocols, such as TCP/IP, SIP, VoIP, and IPsec. In the mobile wireless domain, standards bodies such as 3GPP and 3GPP2 specify standards encompassing radio air interface, network interfaces, and signaling protocols, because they require not only air link interoperability, but also inter-vendor inter-network interoperability for roaming, multi-vendor access, and billing. Vendors and operators have recognized this issue and have formed additional forums to develop standard network reference models for open inter-network interfaces. The WiMAX Forum is an industry-led and non- profit organization formed to develop system profiles, certify, and promote the compatibility and interoperability of broadband wire