ized IMS service design approach. the new architecture and design principles for SDN/NFV. Reusable decomposed VNFs are defined, designed, and added to the VNF catalog. The reusable VNFs can be used for service-specific instan- tiation on an as-needed basis for services. For example, the reusable VNFs may be instantiated for the VoLTE service and can be instantiated separately for a consumer VoIP service. Some VNFs that are part of the SNS (e.g., for IP-carrier interconnect) will be shared across services. Figure 14.15 illustrates the SDSF that is one aspect of the complete virtual service framework for the virtualized IMS service platform. Some points to note about the design include The infrastructure layer is provided by the common cloud infrastructure The NPaaS layer exposes a set of common cloud platform services required that can be used The virtualized solution is a combination of VNFs and PNFs SCC-AS VoLTE AS Subscriber App State I-CSCF Signaling SBC AS CCF HSS-FE I/S-CSCF Conferencing Media SBC w/ Other Carriers Audio I-SBC Transcoding VoLTE Specific VNFs/PNFs Mobility GW CDDF Regulatory LI-IMS Registration Routing HSS-BE State DB (CDR) Control LI-ISBG LI-BGF Mediation ELEAT Storage Shared NetworkService State vTapsaas Subscriber DB Persistence DB Network Platform as a Service Compute Storage Network OpenStack AT&T Integrated Cloud: laaS/PaaS FIGURE 14.15 Logical view of virtualized IMS platform. Building the Network of the Future Use of PNFs will be required for the complete solution Continued interworking with PNFs must be supported 14.4.1.3 Key Design Principles Applied The virtualized IMS service platform design and implementation is based on the following overall virtualization principles: 1. The design should support standard cloud orchestration APIs and should have the ability to evolve in support of emerging cloud management standards 2. Cost reduction of the network infrastructure should be a major consideration 3. The design should meet carrier-grade resiliency and availability requirements 4. I