ations applications applications Simple service middleware Short Audio Payment message notify handle Account Media Third party Presence management management Intermediate service middleware Charging Account Session Connect. UISCP PAM SCF Complex service middleware client client client client client Service function middleware SIP UE P-CSCF I-CSCF S-CSCF Resource function middleware Resource middleware Terminal Router Billing Billing system system Connectivity provider Converged network OSS/BSS Figure 2.6 Implementing the SDP Framework. Service Delivery Platform for the Next-Generation Network invoke resource functions using protocols, such as SIP and Diameter [19]. The pro- tocols hide limited distribution complexities. Hence, these protocols provide lim- ited implementations for the GSOA middleware planes supporting the resource and service functions. The IMS also contributes SIP application servers to the realization of complex services. However, we use the Parlay Service Capability Server (SCS) to encapsu- late these SIP application servers and expose an API. The Parlay SCS implements a complex service enabler offering a complex interface. The intermediate service enablers are implemented using the Parlay Service Capability Functions (SCFs). These SCFs expose their capabilities using their APIs. Both SCS and SCFs are implemented using CORBA-based technologies. These technologies abstract numerous distribution complexities and provide rich standard-based implementa- tions for the GSOA middleware planes supporting intermediate and complex ser- vice enablers. Simple service enablers and interfaces are implemented using the Parlay X Web service APIs. By using Web services the GSOA middleware plane, supporting sim- ple services, is implemented as an Enterprise Service Bus (ESB) [20]. The bus pro- vides functionality to abstract distribution complexities. Using the Web services across the ESB are various Web-based applications. 2.6.2 Alternative Mappings In Parlay X, Web services may be used to directly access netwo