introduction to IMS
The IP Multimedia Subsystem (IMS) is a network functional architecture that is seen as a promising solution for facilitating multimedia service creation and deployment as well as supporting interoperability and network convergence. It was originally designed by the wireless standards body 3rd generation partnership project (3GPP) as an architectural framework for delivering internet protocol (IP) multimedia to mobile users over GPRS, and then expanded to support other networks like Wireless LAN, CDMA2000 and fixed line.
It is commonly admitted that Internet Protocol (IP) is ubiquitous, provides interoperability at a very large scale. These characteristics are driving the internet mutation: If IP was mostly dedicated to the transport of non real time data, it is becoming the foundation of most real time application and services. IMS is using Internet protocols to merge Internet and cellular worlds, and enable rich multimedia communications.
The first version of IMS, written by 3GPP, was about the development and deployment of new services in mobile networks. The specifications were then extended by the European Telecommunication Standards Institute (ETSI) (or to be more accurate by the Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN) standardization body) as a subsystem of the Next Generation Networks (NGNs) project.
It is important to understand that 3GPP describes the support of new applications for mobile operators, while TISPAN adds the wireline operators convergence capabilities, TISPAN defines as well other subsystems like Network Attachment Subsystem (NASS) and the Resource Admission Control Subsystem (RACS). Most of the IMS protocols are standardize by the Internet Engineering Task Force (IETF) (E.g. the Session Initiation Protocol (SIP)).
Other actors are involved in the development of IMS. For example, the Open Mobile Alliance publishes, for interoperability related operation, additional service related requirements (e.g. Push to talk over Cellular (PoC)) (Greenwell, 2007).
IMS is still being defined, and the different standards use different terminologies. If this tutorial won’t explain everything about the several interfaces, and the complex functional entities, it will set a clear overview of the complete NGN/IMS architecture.