y for signaling, voice and data traffic. Generic IP Access network provides connectivity between the MS and the GANC. Up interface that is defined between the GANC and the MS. Co-existence with GERAN and interconnection with the Core Network via A/Gb standardized inter- faces. Call control type services are provided by the core network. Use of AAA server over the Wm interface as defined by 3GPP TS 29.234. Lb interface for supporting location services as defined in 3GPP TS 43.059. CBS-BSC (Cell Broadcast Service-Base Station Controller) interface for supporting cell broadcast services as defined in 3GPP TS 23.401. The handset design is critical to the success of the GAN solution. Consideration needs to be taken to counter the increased power consumption because of two access technologies. When the dual mode handset finds a GAN network, it contacts the GANC for authentication over the broadband IP network. The GAN client in the handset initiates a secure IP tunnel over the IP network to connect to GANC. GANC connects to the private/public IP network and to the core network using the standard interfaces. It also manages subscriber access to the mobile voice and data services from the various WLAN locations. Next Generation Mobile Communications Ecosystem Dual Mode Phone Internet ((o)) VCC AS Figure 11.15 IMS-VCC supporting FMC It connects to the existing MSC and SGSN through the A and Gb interfaces to provide voice and data services. The entire user's traffic is routed via existing GSM core network, simplifying billing process requiring only minimal changes. Upon authentication the MS is allowed to access GSM voice and GPRS data services. Also when the MS is approved, the subscriber's current location information stored in the core network is updated, and from that point on all the services are routed to the handset via GANC rather than RAN. This architecture supports seamless handovers from GSM/GPRS to GAN. These cross-technology handovers are called vertical handovers compared to horizontal handovers, which are be