plement applications, service enablers and the middleware itself. In the SDP framework GSOAs also abstract each other. For instance, the GSOA with simple service enablers', abstract access to the GSOA containing inter- mediate service enablers. The GSOA with intermediate service enablers abstracts End-user Service subscriber Service platform Enterprise Service 3rd party Client Simple Simple service middleware service layer Service Service Service Service Service Service Service 3rd party Client Server Intermediate Intermediate service middleware service layer Service Service Service Service Service Service Service Service Service Server 3rd party Complex service Complex service middleware layer Service Service Service Service Service Service Service Service Service Service function middleware function layer Service Service Service Service Service Service Service function function function function function function function Resource function Resource function middleware layer Resource Resource Resource Resource Resource Resource Resource function function function function function function function Physical resource Resource function layer Resource Resource Resource Resource Resource Resource Resource Converged network OSS/BSS Connectivity provider Figure 2.5 Complete SDP Framework Using GSOAs. Service Delivery Platforms access to the GSOA with complex service enablers. The GSOA containing complex service enablers abstracts all lower function-oriented GSOAs. Each of the SDP framework's GSOAs contain service enablers with interfaces that implement NGN reference points. The RCS reference point is implemented across all layered GSOAs. This is evident in the end-user domain that groups various GSOA applications and service enablers used to implement the reference point. The Rss reference point is implemented across the GSOAs modeling the simple, intermediate, and complex service layers. These GSOAs expose their service enabler interfaces to external IT-using enterprises. These enterprises are represented as service 