ss technologies are connected through the serving gateway (SGW), while all non-3GPP-specific access technologies are typically connected through the packet data network gateway (P-GW) or the evolved packet data gateway (ePDG), which provides extra security functionality for un-trusted access technologies (such as legacy WLANs with no strong built-in security features). Next Generation Mobile Communications Ecosystem: Technology Management for Mobile Communications Saad Z. Asif C 2011 John Wiley & Sons, Ltd. ISBN: 978-0-470-74746-9 Next Generation Mobile Communications Ecosystem Network Management System Internet eNode B Trusted non- Un-trusted non- 3GPP Network 3GPP Network eNode B Figure 11.1 EPS architecture The S-GW acts as a mobility-anchor for mobility within 3GPP-specific access technologies, and also relay traffic between the legacy SGSN accesses and the P-GW. In E-UTRAN the SGW is directly connected to eNode-B through the S1-U interface, while the SGSN is the intermediate node when GERAN/UTRAN is used and it is connected to S-GW via S4 interface. It is important to mention that a mobility management entity (MME) is also incorporated in the architecture for handling control functions such as authentication, security, and mobility in idle mode. EPC also contains network control entities for keeping user subscription information (home subscriber server HSS), determining the identity and privileges of a user and tracking his/her activities (AAA server), and enforcing charging and QoS policies through a PCRF (Policy and Charging Rules Function) [2]. 11.3 E2E WiMAX Architecture The IEEE 802.16 working group was mainly responsible for the air interface specifications (physical and MAC layers) of Fixed and Mobile WiMAX. The WiMAX Forum was created to extend the IEEE 802.16 standard beyond the air interface, designed interoperability specifications, performed device and system certifications and specified network architecture for WiMAX. The Network Working Group (NWG) within the forum is focused on creating networ