r that represents the user without revealing the user's identity. The NAP may deploy an AAA proxy between two NASs in ASN and the AAA in CSN in order to provide security and enhanced manageability. The AAA proxy will also allow the NAP to regulate the AAA attributes received from the visited CSN, and to add additional AAA attributes that may be required by the NASs in the ASN. Note that the CSN hosts the AAA server, whereas the ASN hosts one or more NASs. The PKMv2 protocol is used to perform over-the-air user authentication. The PKMv2 transfers EAP messages over R1 reference point (i.e., the IEEE 802.16-2009 air interface or its evolution) between the MS and the BS in ASN. Privacy Key Management (PKM) Protocol: a client/server model between the base station and mobile station that is used to secure distribution of keying material. CHAPTER 2 WiMAX Network Architecture 2.4 MOBILE IP Mobility support within WiMAX network architecture is based on mobile IP framework. Mobile IP is an IETF protocol that allows mobile users to move from one network to another while maintaining their IP address [1,24]. The two versions of mobile IP protocols,; i.e., Mobile IPv4 and Mobile IPv6, are described in references [9] and [10], respectively. The mobile IP protocol allows transparent routing of IP datagrams on the Internet. Each mobile node is identified by its home address, irre- spective of its current location in the Internet. When away from home, a mobile node is associated with a care-of address, which provides information about its current location. The mobile IP protocol specifies how a mobile node registers with its Home Agent (HA) and how the HA routes datagrams to the mobile node through a tunnel. Using mobile IP, nodes may change their point-of-attachment to the Internet without changing their IP address, allowing the application and transport-layer protocols to seamlessly maintain connection while moving. The general characteristics of mobile IP can be summarized as follows: Transparency of user mobility to the transp