n IMS. IMS also supports roaming and internetworking with existing network services, such as Public Switched Telephone Network (PSTN). Service-level convergence is provided by IMS. Unlicensed Mobile Access GAN originated in 2004 and is associated with Voice over Wi-Fi (VoWiFi) calling. The use of the term GAN was replaced with UMA over time, but UMA is still associated with VoWiFi. This technology allows sending cell phone packets to network access points over the internet instead of only over the air or wirelessly. A UMA-compatible mobile phone can use Wi-Fi if it cannot reach a cellular network. iPhone 5c and later are VoWiFi capable. UMA is air interface-agnostic technology and can use Bluetooth in place of Wi-Fi if needed. The way UMA works is that when the handset is on a local unlicensed LAN, the LAN is available along with the licensed WAN. This enables a smooth transition between the use of LAN and WAN for the voice call. As the user moves around and leaves the LAN coverage area, the call continues as it is roamed to the WAN connection. No user intervention is required. Mobile network operators can set up Wi-Fi hotspots to extend the coverage, say, inside a mall, where WAN coverage is weaker. The user handset must be UMA-compatible for this. 5G Fixed Mobile Convergence Cellular Radio Access Network (RAN) Private Network Base Transceiver Base Station Station (BTS) Controller (BSC) Mobile UMA-Enabled Network Dual-Mode Handset IP Access Network Unlicensed wireless network (e.g., Wi-Fi, Bluetooth...) UMA Network Controller (UNC) Unlicensed Mobile Access (UMA) Network Figure 15.4 - A simplified view of UMA In this section, we looked at the enabler technologies for FMC. Let us look at a simplified view of FMC in Figure 15.5. It shows the logical convergence of the network, device, and services. Voice, Data, Video/TV Service Convergence Communication/B Communication roadcasting Network Device Computer Internet Appliance Fixed/Mobile Mobility Broadband Figure 15.5 - A simplified view of FMC In Figure 15.5, the bo