Thinking About IP Multimedia Subsystem: An Architecture for the Future

Thinking About
IP Multimedia Subsystem:
An Architecture for the Future
The IP Multimedia Subsystem (IMS) is an open, international standard seen. It holds at least the promise for enabling "seamless" mobilityfor Next Generation Networking that supports the delivery of with the full integration of wireline and wireless services. AT&T isVoice over IP (VoIP) and a range of fixed mobile convergence and playing a leading role in the development of the IMS specification,multimedia services. It is not in itself a service but an architecture for working with various standards bodies and trade groups.service delivery. IMS was originally developed by wireless carriers The IMS architecture as defined in the standard alone does not go farwithin the context of the Third Generation Partnership Project (3GPP) enough to enable the creation of secure, flexible and highly reliableand was first defined in 2002. Since then, its particular advantages services. Building on the foundation of the IMS standard, AT&T's IMS-have led to the adoption of IMS by wireline carriers. It provides for based architecture, called the Common Architecture for Real-Timeperson-to-person and person-to-content communication in a variety Services over IP (CARTS), includes many additions and enhancements,of modes. Many industry observers believe it will become the such as improved security and a rich service development platform. standard protocol for telecommunications in the years ahead.
An important driver for IMS is the general trend toward converged Technology Overviewnetworks. Wireline and wireless carriers have been independently The foundation element of IMS is Session Initiation Protocol (SIP), aconverging on IP standards for both voice and data transmission. standard promulgated by the Internet Engineering Task Force (ITEF),Some of the reasons include IP's increased flexibility and the potential with the addition of some 3GPP extensions. The SIP standard is usedit offers for new telecommunications services. IMS also supports the to establish and control voice and multimedia sessions, providing aconvergence of wireline and wireless access. The true vision of IMS is single common internal signaling protocol for all infrastructureto be a convergence platform to enable service providers to offer a components. This greatly simplifies the sign-on and authenticationcommon user experience with converged feature sets that are accessible process for operators and users. It will let carriers offer network-from anywhere, regardless of access technology. "Anytime, anywhere, controlled multimedia services, control the hand-off of a session fromplatform independent, device independent" communications will one network to another or transfer control between different kinds ofbe a fundamental shift in the way that people interact with media and application servers.telecommunications, with less emphasis on the device and IMS has a layered architecture. In the first layer, a "Session Bordermore emphasis on individual preferences. Controller" (SBC) manages the specifics of each access protocolThere is a great deal of interest and support for IMS throughout the involved. SBCs not only provide protocol conversion, but also enforcetelecommunications industry. Since IMS is a standard, its broad the policies needed for call admission control and security. On aacceptance should help drive innovation and economies of scale, separate layer, intelligent application servers support various kinds ofalthough its actual effect on the market is just now beginning to be applications for voice, messaging, presence, etc. By separating theThinking About - IP Multimedia Subsystem, an Architecture for the Future ______________________________________________________________________ 2
session control from the services provided, IMS allows various devices Why Does it Matter?to communicate with each other in a reliable and flexible manner. The The general business drivers for IMS include improvements ininterconnect relations, routing and security architecture thus supports efficiencies that would flow from an environment of converged devicesany potential service that is built on the IMS infrastructure. and services. Traditionally, bringing a new offering to market generallyThe IMS Architecture requires an end-to-end solution, with much duplication of effort.The IMS Architecture Within an IMS environment, the ability to reuse... [download for more]