ime Division Multiplex (TDM) access, cir- cuit-mode transports, service-specific platforms, and rigid Operations Support Systems and Business Support Systems (OSS/BSS). With the evolution of the access, transport, service platforms, and support systems the telco is able to provide improved services that combine multiple media formats including voice, video, and data. Specific examples of telco evolution include Access and transports support packet-based delivery of services, but still interwork with legacy circuit-mode mechanisms. Service platforms are more flexible by using new IT-based tools and software components to develop, deploy, and deliver any type of service. OSS/BSS migrate to loosely integrated IT systems to manage end-to-end business processes, network capabilities, diverse data sources, and service platforms. The current phase of telco evolution is the convergence of Information Technology (IT)-based enterprise networks and Internet networks with the telco. This convergence fuels changes in telco infrastructure, but equally influences changes in the fundamental telco business. For example, new telco business models incorporate external partners, who provide applications or content to enhance telco service offerings to its customers. Also, telco transports are migrating toward pack- et-based mechanisms that operate across the Internet and both fixed and mobile legacy networks. As a result, the telco network is transforming into a Next- Generation Network (NGN) [1]. The NGN is a telco concept that aims to manage and benefit from the integra- tion of telco, IT, and Internet technologies. The NGN is also service centric and aims at providing a rich set of services to customers anywhere, anytime using any capable device. These services not only include, as a subset, legacy voice and data services but also advanced services such as video streaming, instant messaging, and presence-related services. To support the development of these services, the NGN must provide a wealth of service enablers. Service enab