Multimedia-service creation overview

This chapter defines the session initiation protocol (SIP) services, discusses the different approaches to provide such services, and analyzes the tools available for SIP-service creation. SIP provides a basic functionality for the management of sessions, and the location of users and this functionality at the signaling level, together with other protocols at the media level, enable a wide variety of multimedia scenarios. The creation of multimedia services, be they pure signaling services or media services, in the end boils down to manipulating SIP signaling, that is, to creating SIP services. A SIP service is a piece of logic on top of a SIP entity that delivers an enhanced functionality and depending on the required functionality, SIP services may sit on top of a user agent (UA), a proxy, or a back-to-back user agent (B2BUA). SIP is flexible enough to also accommodate other scenarios that allow for having some intelligence in the network, which makes it very appealing to telecom operators, as they can then offer their customers the benefits of being able to leverage Internet-based applications while still retaining the necessary control that allows them to continue making money out of new services. To ease the development of SIP applications, programmers typically use application programming interfaces (APIs) that encapsulate specific aspects of the SIP functionality so that programmers can concentrate on the application service logic. Some of the standardized API technologies used in the context of SIP-application development include JAIN (Java APIs for integrated networks) SIP, JAIN session description protocol (SDP), and SIP servlets.