CHAPTER WiMAX Network Architecture 2 INTRODUCTION The IEEE 802.16-2009 standard only defines physical and medium access control layer protocols. This approach might have worked well for technologies such as Ethernet and Wi-Fi, relying on other bodies such as the Internet Engineering Task Force (IETF) i to set the standards for higher layer protocols such as TCP/IP [1], SIP [2], and Ipsec [3], it cannot be generalized to cellular standards. Standard developing organizations such as 3GPP and 3GPP2 specify end-to-end wireless access systems including a wide range of interfaces and network protocols because practical systems require not only the air link interoperability but also inter-vendor and inter-network interoperability for roaming, multi-vendor access networks, and inter-operator billing. WiMAX vendors and operators have recognized this issue and have established additional industry groups to develop standard network reference models for open network interfaces. Examples of these groups include WiMAX Forum's Network Working Group, ii which is focused on creating higher-level networking specifications for fixed, nomadic, portable, and