is not available, the NG-RAN routes the UE to a default AMF instance [3,15]. Enabling network slicing in 5G requires native support from the overall system architecture. As shown in Fig. 1.16, the overall architecture consists of three fundamental layers: the infra- structure layer, network slice layer, and network management layer. The infrastructure layer provides the physical and virtualized resources, for instance, computing resource, storage resource, and connectivity. The network slice layer is located above the infrastructure layer and provides necessary NFs, tools and mechanisms to form end-to-end logical networks via NSIs. The network management layer contains the generic BSS/OSS and network slice man- agement (NSM) system, which manages network slicing and ensures satisfaction of the SLA requirements. The overall architecture has the following key features: Common infrastructure: Network slicing is different than a dedicated network solu- tion that uses physically isolated and static network resources to support tenants. Network slicing promotes the use of a common infrastructure among tenants oper- ated by the same operator. It helps to achieve higher resource utilization efficiency and to reduce the service time to market. Moreover, such design is beneficial for long-term technology evolution as well as for maintaining a dynamic ecosystem. On-demand customization: Each technical domain in an NSI has different customization capabilities, which are coordinated through the NSM system during the process of net- work slice template (NST) design, NSI deployment, and operation and management. Each technical domain can perform an independent customization process in terms of design schemes to achieve an effective balance between the simplicity needed by com- mercial practice and architectural complexity. Isolation: The overall architecture supports the isolation of NSIs, including resource iso- lation, operation and management isolation, and security isolation. The NSIs can be either physically or logically i