IP Multimedia Subsystem (IMS) defines a standard framework for the deployment of next generation IP-based application services. It defines how these services connect and communicate with the underlying telecommunications network(s) and how they integrate with the network provider’s back-end systems.

The IMS specifications define the functions to handle the signaling and user traffic for multimedia applications. The main signaling protocol in IMS is the Session Initiation Protocol (SIP). In IMS, the use of SIP facilitates interconnectivity between fixed and mobile networks, allowing fixed and mobile users to communicate using voice, video, chat, and online gaming, and to take advantage of functionality such as Push to Talk, Instant Messaging (IM), and Presence (whether and how a user is available, and how the user wants to be contacted).

IMS is comprised of a layered and unified architecture that manages media as it moves through the network and provides the systems integration needed to provide any IP Multimedia services for and between any set of wire line and wireless end-users. The core network contains reusable functions that manage and route media to media and application servers for processing. Application servers host the services and IMS defines the service control, routing, protocols, and charging processes across the network, without regard to input device or data format.