lated with the UPF that terminates N3. gNB/RAN PCSCF N1N2 TranferRegAck PduSessionSetupRsp(NGAP- PDUSessionResourceSetupReq) PDUSessionSetupRsp PDUSessionSetupRsp PDU Session Update SM Context Req N4 SX Modification Req N4 SX Modification Resp PDU Session Update SM Context Req Figure 7.21 - IMS PDU attach procedure - part 4 Figure 7.22 shows a wire capture of the SMF and NRF transaction for the discovery of an AMF; the requestor and target field can be used to identify which network function is requesting the details of the target network function from the NRF. IMS 5G PDU session establishment SMF<->NRF ([19]/nnrf-disc/v1/nf-instances?dnn=ims&requester-nf-type=SMF&target-nf-type=AMF HyperText Transfer Protocol 2 Stream: DATA, Stream ID: 5, Length 0 JavaScript Object Notation: application/json Object Member Key: validityPeriod Member Key: infInstances Array Object Member Key: infInstanceId Member Key: nfType String value: AMF Key: nfType Member Key: nfStatus String value: REGISTERED Key: nfStatus Member Key: plmnList Array Object Member Key: mcc String value: 310 Key: mcc Member Key: mnc String value: 260 Key: mnc Key: plmnList Member Key: sNssais Array Object Member Key: sst Number value: 1 Key: sst Key: sNssais > Member Key: fqdn > Member Key: priority > Member Key: capacity > Member Key: load Member Key: locality String value: west.amf Key: locality Member Key: amfInfo Object Member Key: amfSetId String value: 100 Key: amfSetId Member Key: amfRegionId String value: 0A Key: amfRegionId > Member Key: guamiList > Member Key: tailist Key: amfInfo > Member Key: infServicePersistence > Member Key: infServices Key: infInstances Figure 7.22 - Packet capture SMF to NRF discovery Figure 7.23 shows the content of the N1N2 message transfer transaction between the SMF and the AMF. Some key fields, such as the Always on indicator and protocol configuration options, depict the kind of information exchanged with this message: Packet Core Procedures SMF->AMF [22] N1N2 Message Transfer (n2msg content) > PDU session type - Select