With fixed-mobile convergence -- the seamless switching between cellular and local networks for mobile users – becoming more prevalent, it’s a good time to bone up on some related terms you might run across. Here’s a sampler:

IP Multimedia Subsystem (IMS)  -- Considered the future protocol of choice that will eventually provide all multimedia services with session control. Relies on IP for transport and provides users with access to multimedia services, including voice, video and text-based applications. It can also connect a wireline subscriber to a wireless subscriber, and offer session control and security when handing off a call between WLAN and mobile networks. Relies on SIP for session control in both mobile and fixed wireline networks, and offers users SIP-like presence and availability information.

Unlicensed mobile access (UMA) – Considered a supplement or intermediary step to IMS. UMA is built to provide seamless session hand-offs only between a Wi-Fi and mobile network, and offers session control and security when handing off a call. Does not rely on SIP for session control. Authentication is device-specific. Considered by some analysts to be the predominant technology deployed today to implement seamless FMC between wireless LAN and 2G cellular networks. Can also now support 3G, and is backed by the 3GPP, supports migration to IMS and femtocells.

Femtocells – Indoor 3G base stations considered to be a main driver of FMC. Provide a cheaper alternative to cellular phones inside buildings – indoor and outdoor coverage are on the same spectrum so dual-mode cellular/WLAN phones are not required. Connect to cellular networks using customer's own broadband connections, countering alternatives such as voice over Wi-Fi, where users make low-cost calls on their own indoor Wi-Fi network.

Voice Call Continuity (VCC) – Emerging 3GPP hand-off standard tied to IMS. Transfers calls from an IP network to the mobile switched network. Describes how a voice call can be maintained as a mobile phone moves between circuit-switched and packet-switched radio domains. Considered critical for the introduction of enterprise FMC services.