oup, which is focused on creating higher-level networking specifications for fixed, nomadic, portable, and mobile WiMAX systems beyond what is defined in the IEEE 802.16 standards, and the Service Provider Working Group, iii which defines requirements and priorities according to operators' needs. The WiMAX network architecture is a non-hierarchical end-to-end all-IP framework for mobile WiMAX systems that is based on maximal use of non-proprietary standard IP protocols, and is compatible with external service enablers such as IP Multimedia Subsystem [4]. A distinctive feature of WiMAX network architecture is decoupling of access, connectivity, and service networks to allow combination of multi-vendor implementations of physical network entities, as long as they comply with the normative protocols and procedures across applicable interfaces that are defined in the WiMAX network specification. This chapter provides a top-down systematic description of WiMAX network architecture, starting at the most general level and working toward details or specifics of the network components and their interconnections. We further provide an overview of 3GPP evolved network architecture to enable the readers to contrast the corresponding procedures and functionalities. 2.1 DESIGN PRINCIPLES OF WIMAX NETWORK ARCHITECTURE In this section, the principles based on which the WiMAX network architecture has been designed are described. The tenets are divided into different categories and are applicable to all releases of the WiMAX network architecture [5]. http://www.ietf.org "http://www.wimaxforum.org/about/network-working-group-nwg ""http://www.wimaxforum.org/about/service-provider-working-group-spwg Mobile WiMAX. DOI: 10.1016/B978-0-12-374964-2.10002-5 Copyright © 2011 Elsevier Inc. All rights reserved. CHAPTER 2 WiMAX Network Architecture The architecture and network reference model (NRM) accommodate all usage models provi- sioned for WiMAX systems [6]. The packet-switched architecture is based on the IEEE 802.16 standard and its am