The IP Multimedia Subsystem (IMS) is an architectural framework for delivering Internet Protocol (IP) multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project (3GPP), as a part of the vision for evolving mobile networks beyond GSM. Its original formulation in 3GPP Release 5 represented an approach to delivering "Internet services" over GPRS in the transition from second generation (2G) to third generation (3G) technology. This vision was later updated by 3GPP, 3GPP2 and the Telecoms and Internet Converged Services and Protocols for Advanced Networks (TISPAN) by requiring support of networks other than GPRS, such as Wireless LAN (3GPP Release 6), CDMA2000 (3GPP2) and fixed line (3GPP Release 7 and TISPAN R1.1).
IMS is an important component of 3GPP evolution, and its architecture is rapidly maturing. IMS is a service platform that allows operators to support IP multimedia applications. Potential applications include video sharing, Push-to-Talk over Cellular (PoC), Voice over IP (VoIP), streaming video, interactive gaming, etc. IMS by itself does not provide all these applications. Rather, it provides a framework of application servers, subscriber databases, and gateways to make them possible. The exact services will depend on user demand, the cellular operators and the application developers.
To ease the integration with the Internet, IMS uses Internet Engineering Task Force (IETF) open standard core networking protocols wherever possible (e.g. Session Initiation Protocol [SIP]). According to the 3GPP, IMS is not intended to standardize applications but rather to aid the access of multimedia and voice applications from wireless and wireline terminals, (i.e. create a form of Fixed-Mobile Convergence [FMC]). This is done by having a horizontal control layer that isolates the access network from the service layer.
IMS is relatively independent of the radio-access network and can, and likely will, be used by other radio-access networks or wireline networks. Operators are already trialing IMS and one initial application under consideration – Push-to-Talk over Cellular – is being specified by the Open Mobile Alliance (OMA). Other applications include picture and video sharing that occur in parallel with voice communications. Operators looking to roll out VoIP over networks could also use IMS.
As shown in following figure, IMS operates just outside the packet core.
IP Multimedia Subsystem
Although originally specified by 3GPP, a number of other organizations around the world support IMS. In addition to the Internet Engineering Task Force (IETF), which specifies key protocols such as SIP, and the Open Mobile Alliance (OMA), which specifies end-to-end service-layer applications, other organizations supporting IMS include the GSM Association (GSMA), the European Telecommunications Standards Institute (ETSI), CableLabs, 3rd Generation Partnership Project 2 (3GPP2), the Parlay Group, the International Telecommunication Union (ITU), the American National Standards Institute (ANSI), the Telecoms and Internet Converged Services and Protocols for Advanced Networks (TISPAN), and the Java Community Process (JCP).
According to an ABI Research analyst, an advantage of IMS is that it enables rapid development and deployment of new services and is essential to the success of mobile and fixed operators who are losing revenue from traditional sources. It is forecast by ABI that mobile operators will reap $300 billion revenues over five years ending in 2013 due to new services delivered with IMS.
The benefits of using IMS include handling all communication in the packet domain, tighter integration with the Internet, and a lower cost infrastructure that is based on IP building blocks used for both voice and data services. This allows operators to potentially deliver data and voice services at lower cost, in turn providing these services at lower prices and further driving demand and usage.
IMS applications can reside either in the operator’s network or in third-party networks.