the UPF. 3) The AMF starts the PDU resource session establishment procedure by transmitting the information allowing us to configure the radio node level, the PDU session (tunnel identifier and the IP address of the UPF function) and the resource reservation (scheduling rules) to the NG-RAN node. The information is transmitted in the NGAP PDU SESSION RESOURCE SETUP REQUEST message. 4) The radio node transmits the information concerning the establishment of the DRB data radio bearer in the RRC Reconfiguration message to the mobile. 5) The mobile acknowledges the receipt of the DRB configuration via the RRC ReconfigurationComplete message. 6) The radio node transmits the configuration information of the UPF transport plan (TEID, IP address of the radio node) to complete the routing table to the AMF function. The AMF function transfers this information to the SMF function, which manages the UPF function. RRC SetupComplete INITIAL UE MESSAGE NAS PDU Session Establishment Request (S-NSSAI, PDU Session ID, Request Type, RAT, TAI) NAS PDU Session Establishment Request PDU SESSION RESOURCE SETUP RRC Reconfiguration RRC ReconfigurationComplete PDU SESSION RESOURCE SETUP RESPONSE Figure 3.15. The procedure for establishing a PDU session NG-RAN Network - Procedures 3.2.4.2. Continuity of the session service The continuity of the service of a PDU session is configured during the establishment of the PDU session according to the value of the SSC mode. The continuity of the service makes it possible to guarantee (or not) the conservation of the IP address in the event of mobile mobility, according to one of the following three modes (Figure 3.16): - SSC mode 1: the core network ensures the continuity of service by keeping the IP address for an IP session; - SSC mode 2: the core network releases the existing PDU session and therefore the mobile connection to re-establish it on another UPF function. In the case of an IP session, the IP address assigned to the mobile will change; - SSC mode 3: the core network establishes two PDU