Written by: Piotr Kessler

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The success of IMS will largely depend on the availability of new services in end-user equipment. Strong focus on terminals is thus especially important to ensure that IMS services remain independent of access and terminal type.

Implementations of IMS applications in terminals must address two disparate aspects: technology and end-user experience. Accordingly, Ericsson's solution partitions IMS applications into two layers consisting of an IMS client framework (which essentially hides IMS technology behind a high-level API) and IMS applications.

The author describes Ericsson's realization of the IMS client framework

Background
"No one is an isolated island," wrote British poet John Donne in 1623, indicating, among other things, that it is human nature to want to belong to a social context. Previously, our "worlds" were defined to a great extent by small communities in our immediate surroundings, whereas today they are expanding to include the ability to communicate and interact with just about anybody, anywhere, at any time, and using any communication device.

For most people, exposure to this new communication paradigm began with the introduction of internet access to the home.

On the one hand, it has taught us how easy it is to develop and use new communication services. But on the other hand, we see how difficult it is to create and use a consistent suite of communication services that can interoperate with others' suites of communication services. Indeed, having myriad applications on your computer does not offer the same simplicity of service you experience when using a phone to set up a call. Nor can you expect to reach all your contacts in the same easy way as you can currently do from your phone book. Therefore, looking forward, the challenge is to ensure that communication applications will work together, simply, and on any communication device.

The solution calls for an architecture for advanced network-based multimedia communication services - one that merges technologies and fuses the advantages of the internet domain with those of the telecommunications domain. This architecture, the IP Multimedia Subsystem (IMS), has already been defined and standardized by the Third Generation Partnership Project (3GPP).

IMS defines a framework that facilitates development and deployment of any type of multimedia service. The IMS framework includes or addresses

• end-to-end service (that is, it takes into
• account all the nodes that are needed to
• realize service);
• reachability, using similar (or possibly the
• same) addressing mechanisms;
• mobility;
• interoperability;
• convergence;
• quality of service (QoS);
• multimedia connections;
• security; and
• charging.

Examples of services that have been standardized on top of IMS include OMA presence and group list management, OMA Push-to-Talk over Cellular (PoC), 3GPP combinational services (CSI), OMA Instant Messaging, and TISPAN/3GPP multimedia telephony for IMS (MMTel).