er level of abstraction than the Web services-based SOA [3]. The GSOA is a distributed system architecture that provides client entities with technology-independent interfaces to services. These clients represent applications that require use of one or more service to provide some form of functionality to customers. The GSOA, with clients and services, is illustrated in Figure 2.3. Service Delivery Platform for the Next-Generation Network Peer to peer Application Application Application Application interface interface Middleware plane Service interfaces Service Service Service Service Figure 2.3 Representation of the GSOA. The GSOA contains diverse services that abstract various complexities of all underlying support facilities. For instance, services abstract the access and usage of other software entities, databases, network resources, and network capabilities. As a result, services hide the technology and distribution of underlying resources they abstract. Services also abstract complexities from applications accessing their func- tions. For instance, services offer interfaces to hide their implementation and distri- bution from applications. Hence, GSOA services are similar to service enablers required by an SDP or NGN service platform. Like the Web services SOA, the GSOA models a distributed system. So, the GSOA includes abstractions to manage the complexities associated with distribu- tion. A key abstraction is the middleware plane. The middleware plane enables applications across the GSOA to communicate in a "peer-to-peer" manner via their own interfaces. In addition, communication between applications and services are perceived as direct client-server communication via service interfaces. As a result, the middleware plane hides communication details between applications and services. These details include the diverse transports, computing platforms, and devices that connect applications and services together. Besides hiding distribution, the middleware plane provides its own services with interfaces that 