nd local policy information, the source AMF decides to send the NGAP Reroute NAS Message to the gNB entity SO that it formulates a new request for attachment to the target AMF function. NG-RAN Network - Procedures Target Target RRC SetupRequestComplete (NAS Registration Request, Registration Type, 5G Id, Last TAI Initial UE Message Requested S-NSSAI, UE Capability, List of PDU Sessions) Messages UDM/NSSF/NRF Namf Communication N1MessageNotify AMF Configuration Update AMF Configuration Update Acknowledge Register procedure (Figures 3.7 and 3.8) Figure 3.13. The registration procedure option A: selection and reallocation to a target AMF source Target RRC SetupRequestComplete (NAS Registration Request, Registration Type, 5G Id, Last TAI Initial UE Message Requested S-NSSAI, UE Capability, List of PDU Sessions) Messages UDM/NSSF/NRF Reroute NAS Message Initial UE Message Register Procedure (Figures 3.7 and 3.8) Figure 3.14. The registration procedure - option B: selection and reallocation of the AMF function by the gNB The context of the mobile UE must be transmitted to the target AMF function. If the UE context is transmitted to the target AMF in the Reroute NAS Message carried by the Namf_Communication_N1MessageNotify message, then the target AMF can start the authentication procedure. If the target AMF does not have context regarding the mobile UE, the source AMF sends the amf_Communication_UEContextTransfer message to the target AMF to retrieve it. NG-RAN and 5G-NR 3.2.4. The procedure for establishing a PDU session During the registration phase, the mobile transmits the NAASI indicator of the desired network in the RRC SetupRequestComplete request. The network core determines the authorized network slice, depending on the radio access network. Once registered, the mobile will be able to establish a PDU (Protocol Data Unit) session for each S-NSSAI network slice. A PDU block is a structured data block consisting of one or more bytes. A PDU session is defined by three parameters: an S-NSSAI network slice indicator