What is Home Subscriber Server

Although promised for some time now, advanced multimedia services for mobile devices were not yet a reality. With IMS (IP Multimedia Subsystem), the fundaments for advanced multimedia services based on IP will be laid. However, there are still a lot of confusions about IMS that may hinder its success. In this chapter, a comprehensible presentation of IMS together with its potential regarding the development of advanced services is given. The chapter starts with a justification of the existence of IMS. The necessary adaptations of SIP (Session Initiation Protocol) are explained. A concise description of IMS will be provided. Next, the deployment of IMS in fixed – mobile environments will be examined thoroughly. The heart of the chapter is the presentation of the strengths of IMS, that is, what can IMS be used for. A few advanced multimedia service scenarios are given as illustration. The chapter will also consider the most important but yet neglected component of the whole IMS, namely the IMS client. The chapter concludes with a summary of the challenges that must be resolved.