IMS Environment Overview
IP multimedia subsystem (IMS) is a flexible network architecture that allows providers to introduce rich multimedia services across both next-generation packet-switched and traditional circuit-switched networks. It uses open interfaces and functional components that can be assembled flexibly to support real-time interactive services and applications.
Third Generation Partnership Project (3GPP) developed IMS to provide a standards-based architecture for mobile carriers to migrate to their next-generation networks that will support applications that combine voice, video, and data functionality. The European Telecommunications Standards Institute (ETSI) created Telecommunications and Internet Converged Services and Protocols for Advanced Networks (TISPAN) to extend IMS support to fixed-line carriers. This extension is commonly called fixed mobile convergence (FMC). IMS/FMC allows subscribers to access any network (wireless or fixed) from any device (computer, PDA, or cell phone) and be able to move seamlessly from one network to another.
Figure 1 shows, at a high level, a converged IMS network that manages and controls the movement of subscribers between fixed and wireless networks.
By itself, IMS does not specify new services; rather, it provides a framework for network operators to build and launch their services regardless of access method. The IMS architecture simplifies network operations and allows providers to focus on service introduction and business opportunities. For example, an IMS architecture could allow fixed and mobile users to communicate using voice, video, chat, and online gaming, and to take advantage of functionality such as Push-to-Talk over Cellular (PoC; the ability to quickly arrange meetings through a walkie-talkie mechanism), instant messaging, and presence (whether and how a subscriber is available, and how the subscriber wants to be contacted).