connection for a data service, it sends the RRC Service Request to the AMF with the S-NSSAI flag. The AMF selects the most suitable SMF. On NG-RAN, the gNB-CU entity selects the gNB-DU entity based on the S-NSSAI flag. The division of the network on radio access is defined by: - common RRC functions (management of sharing of radio resources between slices) and specific RRC functions (DRX, eDRX, timers, QoS, etc.); - PDCP, RLC, common or specific functions (header compressions, acknowledgment, etc.); - sequencing (MAC function) and prioritization on the physical layer. The objective of virtualizing the network is to provide network flexibility and dynamic adaptation to the needs of different users, in order to meet performance indicators specific to the services requested (latency, throughput, packet loss, etc.). This flexibility is provided by an orchestrator which supervises the network functions and delegates the traffic management to the radio controllers (SD-RAN Software Defined RAN) and network controllers (SDN: Software Defined Networking). In addition, virtualization allows isolation of the different slices. 1.7. References All standards can be downloaded from the ETSI website: https://www.etsi. org/standards. 3GPP TS 37.340 Universal Mobile Telecommunications System (UMTS); LTE; 5G; NR; Multi-connectivity; Overall description; Stage-2 Version 15.3.0 Release 15 3GPP TS 38.401 5G - NG-RAN: Architecture description Version 15.2.0 Release 15 3GPP TS 24.501 5G - Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 Version 15.0.0 Release 15 3GPP TS 23.003 Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); Numbering, addressing and identification Version 15.5.0 Release 15 NG-RAN Network - Functional Architecture 3GPP TS 33.501 5G - Security architecture and procedures for 5G System Version 15.2.0 Release 15 NG-RAN Network - Protocol Architecture 2.1. The protocol architecture of the radio interface The NG-RAN radio access network is divided i