Internet Protocol (IP) multimedia subsystem (IMS) is a next-generation communication network for carriers from the 3rd Generation Partnership Project (3GPP) that uses the IP protocol as its foundation. As is known, 3GPP is a cooperation of international standards bodies for the promotion of cellular systems that support high-speed data, known as “3rd-Generation” (3G) systems. The IMS supports data, video, Session Initiation Protocol (SIP) based voice over IP (VoIP) and non-SIP packetized voice, such as the International Telecommunications Union (ITU) H.323 standard and the Media Gateway Control Protocol (MGCP). IMS was also designed to integrate with the Public Switched Telephone Network (PSTN) and provide traditional telephony services.
The IMS was conceived to offer support for a wide variety of types of communication sessions whether over wireless or wireline, including instant messaging (IM), push-to-talk, videoconferencing and video-on-demand (VOD). The IMS thus blends services for converged wireline and wireless networks. The IMS architecture separates the service layer from the session and access layers. The defining of clear application programming interfaces (APIs) between the different layers makes service creation easier for third parties and easily deployable by service providers.
Due at least to the fact that an IMS session is capable of supporting a wide variety of communication protocols and platforms, a need exists for providing flexibility to users in terms of migration between communication devices employed during an IMS session.