rs. As a result, the service stratum also includes OSS/BSS capabilities to securely manage and administrate exposure and interworking of services and service enablers. Customer Other applications Service stratum service and services platforms Other Customer Network stratum devices transport networks Figure 2.1 Modified NGN Reference Model. Service Delivery Platform for the Next-Generation Network 2.2.1 Standardization We add reference points to the NGN reference model in Figure 2.1, to formalize relationships between and across the strata. These reference points promote stan- dardization of the NGN. The RCS reference point specifies the relationship between customers and the NGN service platform. The RSS reference point ensures external access to the NGN service platform and its enablers are standardized. The RST refer- ence point provides the service platform with unified standard-based access to underlying network functions. The RCT and RTT reference points enable standard- ized end-to-end delivery of services across all customer terminals and converged networks. The NGN reference model does not prescribe specific technologies to imple- ment strata and reference points. However, it is essential that service enabler technologies have open standards-based interfaces to ensure diverse NGN imple- mentations remain consistent and interoperability. A current example of standard- izing the network strata reference points, RCT and RTT, is the Internet Protocol Multimedia Subsystem (IMS) [6]. The IMS defines necessary network functions that satisfy most network stra- tum requirements. These functions provide various capabilities, such as managing access control, mobility, data management, and service triggering. The IMS func- tions communicate using various standards-based telco and Internet protocols, such as adapting to CAMEL Application Part (CAP) [7] and a profile of the Session Initiation Protocol (SIP) [8]. The collection of these protocols implements the RCT and RTT reference points. The IMS also attempts to impl