(WAC) or ASN Gateway that provides connectivity to the end users with the rest of the network. The architecture allows several options for backhauling including point-to-point microwave from the base stations to the aggregator. The aggregator is just like a switch that accumulates traffic and sends it to the WAC. The CSN in addition to AAA will include MIB, DHCP and DNS servers. The AAA performs authentication, authorization, accounting for subscribers. The MIB (Management Information Base) is used by the network operator to software upgrade managed subscriber stations. DHCP allocates IP addresses to the end users while DNP provide address resolution service (translation from host name to IP address). The CPE could be PCMCIA cards for laptops, outdoor wall mounted units or indoor desk units; it does not include the laptop or desktop computers. 11.3.2 Mobile WiMAX Network Architecture Figure 11.3 shows the topology that will support mobility in addition to fixed and portability for the users. The key elements that are required to support mobility are Home Agent and Foreign Agent. It also shows Media Gateways (Soft Switches) and their controllers (MGC) and SIP (Session Initiation Protocol) servers for telephony services (VoIP), connectivity to PSTN and multimedia services. The architecture also supports Mobile IP that allows subscribers to roam to other networks and still be reachable from their home network. Mobility between the ASN-GW and HA is handled with the proxy Mobile IP protocol (PMIP). A WiMAX base station can connect to any ASN Gateway that it can reach via IP connectivity using 1 PMIP provides similar functionality to that of Mobile IP, however it does not require any modifications to the mobile host's network stack, i.e. the mobility is taken care of by the network. Mobile IP is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address. Next Generation Mobile Communications Ecosystem Foreign Agent Agent Base Station Internet Firewall Switch/Aggre