ation Telecom services. This service control architecture can indeed be incorporated into the larger scheme of things of an advanced next- generation SDP, but here, we keep that out of the scope of this chapter. IMS defines an overlay service architecture that merges Internet services into Telecom service development. The IMS architecture supports a wide range of ser- vices including traditional legacy services (Intelligent Network (IN) services), next- generation IMS services with SIP [7] as the underlying protocol, as well as SOA-based Web Services. Introduced by 3GPP [19], IMS uses the SIP in the signal- ing plane to provide assistance and control for multimedia sessions, established between two communicating peers. Service control in IMS architecture is actually delegated to an entity called the Service Capability Interaction Manager (SCIM) [6]. The SCIM is envisioned to coordinate the diverse capabilities from different service domains, and orchestrate the interactions between them, using SIP as the control protocol in the signaling layer.* The SCIM can loosely be likened to an SIP-based AS that performs the functionality of runtime orchestration of interactions between capabilities in the converged network. Such interactions can occur between SIP features and legacy signaling features (e.g., SS7), between components that are wholly implemented as SIP proxies or user agents [7], or even with external business capabilities that are exposed using Web services (WSDL, Simple Object Access Protocol (SOAP)). Surprisingly, the 3GPP standard only includes a loose definition of SCIM on its role of interaction management. According to this definition, an AS may contain SCIM functionality and other ASs. The SCIM functionality is an application which performs the role of interaction management. The implementation of the SCIM has been left up to the vendors to suite their individual application require- ments. As a result, the literature has very little on the design principles of an SCIM that one can refer to. Thus, the