, system scalability, mobility management, wireless networking, transport services, in-network caching, and network management. 142 Chapter 1 Nnssf Nausf Figure 1.69 5G system service-based reference architecture [3]. sessions to be defined prior to a PDU session request by a UE. This de-coupling allows dynamic and policy-based interconnection of UE flows with slices provisioned in the core net- work. The SMF is used to handle IP anchor point selection and addressing functionality, man- agement of the user-plane state in the UPFs such as in uplink classifier and branching point functions during PDU session establishment, modification and termination, and interaction with RAN to allow PDU session forwarding in UL/DL to the respective data networks. In the user plane, UE's PDUs are tunneled to the RAN using the 5G RAN protocols. From the RAN perspective, the PDU's five-tuple header information (IP source/destination, port, protocol, etc.) is used to map the flow to an appropriate tunnel from RAN to UPF. 1.2.2.1 Reference Architecture: Network Entities and Interfaces The 5G core network architecture comprises a number of NFs, some of which have newly been introduced. In this section, we provide a brief functional description of these NFs. Fig. 1.69 illustrates the 5GC service-based reference architecture. Service-based interfaces are used within the control plane. The main 5GC network entities include the following [3]: Fig. 1.70 depicts the 5G system architecture in the non-roaming case, using the reference- point representation showing how various NFs interact with each other. Note that the NF is a 3GPP-adopted processing function in next generation network that has both functional behavior and interface. An NF can be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform such as cloud infrastructure. 5G Network Architecture (R)AN PDN (Internet) Figure 1.70 Non-roaming reference-po