multaneous IPv4 and IPv6 connections. It also needs to support vertical or inter-technology handovers at different vehicular speeds, for example, to WiFi, 3GPP, 3GPP2, and SO on, when such capability is enabled in multi-mode terminals [4]. 11.4.2.1 Handoffs and Power Management The two critical issues to support mobility are power management and handoffs. Mobile WiMAX has incorporated features like sleep mode and idle mode and hard and soft handovers to support mobility. 11.4.2.1.1 Handoffs There are three handoff methods supported within the 802.16e standard namely Hard Handoff (HHO), Fast Base Station Switching (FBSS) and Macro Diversity Handover (MDHO). The HHO is mandatory while FBSS and MDHO are two optional modes [3]: HHO means the session has to reestablished once the subscriber is changing the frequency or moving from the coverage area of one vendor or operator to another that is, break before make. In FBSS, the MS continuously monitors the base stations in the active set. A FBSS handoff process begins as soon the MS realizes that the Anchor BS (defined within the active set) that it is currently using to communicate the messages may change. This transition from one Anchor BS to another (i.e., BS switching) takes place without invocating explicit HO signaling messages. The active set update is performed by the MS and BS and then the MS selects one BS from the set to be the Anchor BS which the MS reports on CQICH (Channel Quality Indicator Channel) or MS initiated HO request message. Next Generation Mobile Communications Ecosystem An important requirement of FBSS is that the data is simultaneously transmitted to all the members of an active set of BSs that are able to serve the MS. When operating in MDHO, the MS communicates with all BSs in the active set of uplink and downlink unicast messages and traffic. A MDHO begins when a MS decides to transmit or receive unicast messages and traffic from multiple BSs in the same time interval. For downlink MDHO, two or more BSs provide synchronized transmission to M