Telecom Tutorials by Samir Amberkar

Overall References: 3GPP TS 23.502:4.2.2, 4.3.2, 38.508-1:4.5.2, 4.5A.2, and 38.401:8.1, 8.9.1, 8.9.2.

You may further compare it with LTE - end-to-end UE initial attach for similarities and differences.

If you are interested only in messages, it is available here.

USIM     UE     gNB_DU     gNB_CU_CP     gNB_CU_UP     AMF     SMF     UPF     AUSF     IP_NET    Protocol/Interface presentation UICC Uu F1 E1 NG-C NG-U IP IP Reference point presentation N1 N2 N3 N11 N12 N4 UE powers on, modem activation. 27.007MN-AT:8.2 "Set phone functionality +CFUN", 27.007MN-AT:7.3 "PLMN selection +COPS" USIM activation and fetching PLMN data 31.102USIM:4 "Contents of the Files", 31.102USIM:5 "Application protocol" Band selection, Frequency scanning, Cell search, PLMN selection, Initial cell selection, Synchronisation (SSB/MIB) and SIB1 reception 38.304IDLE MODE:5.1 "PLMN Selection", 38.304IDLE MODE:5.2 "Cell Selection", 23.122NAS:4.4 "PLMN selection process", 38.331RRC:5.2.2 "System Information Acquisition", 38.213PHY:4 "Synchronisation procedures", 38.211PHY:7.4.3 "SS/PBCH block", 38.213PHY:13 "UE procedure for monitoring Type0-PDCCH CSS sets" PHY Identity SI RNTI Downlink PBCH mapped to BCH mapped to BCCH 38.202PHY:6.1 "Uplink", 38.202PHY:6.2 "Downlink", 38.300RAN:6.2.3 "Mapping to Transport Channels" 5GSM-PDU-SESSION-INACTIVE 5GMM-DEREGISTERED RRC-IDLE NAS(5GMM) requests RRC Connection 23.502NAS:4.2.2.2 "Registration procedures", 24.501NAS:5.3.1 "Establisment of N1", 38.331RRC:5.3.3 "RRC connection establishment" 5GMM-REGISTERED-INITIATED RRC-IDLE Uplink PRACH mapped to RACH Select RA-RNTI Random Access Preamble (msg1) over RACH 38.321MAC:5.1 "Random Access procedure", 38.213PHY:8 "Random Access procedure" Downlink PDSCH mapped to DL-SCH mapped to CCCH (SRB0) PHY Identity RA RNTI PDCCH monitoring with RA-RNTI DL DCI (format 1) over PDCCH Random Access Response (msg2) over PDSCH 38.213PHY:10.1 "UE procedure for determining physical downlink control channel assignment", 38.214PHY:5.1 "UE procedure for receiving PDSCH" Got Temporary C-RNTI, UL grant, TA RRC Setup Request (msg3) over PUSCH 38.321MAC:5.4 "UL-SCH data transfer", 38.214PHY:6.1 "UE procedure for transmitting PUSCH" INITIAL UL RRC MESSAGE TRANSFER [RRC Setup Request] 38.473F1:8.4.1 "Initial UL RRC Message Transfer" DL RRC MESSAGE TRANSFER [RRC Setup] 38.473F1:8.4.2 "DL RRC Message Transfer" PHY Identity Temporary C-RNTI PDCCH monitoring with Temporary C-RNTI DL DCI (format 1) over PDCCH RRC Setup (msg4) over PDSCH 38.321MAC:5.3 "DL-SCH data transfer" Got SRB1 configuration 38.331RRC:5.3.3.4 "Reception of RRCSetup by UE" RRC-CONNECTED Downlink PDSCH mapped to DL-SCH mapped to CCCH (SRB1) Uplink DCCH (SRB1) mapped to UL-SCH mapped to PUSCH PHY Identity C-RNTI SR over PUCCH (Request UL allocation) 38.213PHY:9.2 "UCI reporting in PUCCH" PDCCH monitoring with C-RNTI UL DCI (format 0) over PDCCH RRC Setup Complete [5GMM REGISTRATION REQUEST] over PUSCH 38.331RRC:5.3.3.4 "Reception of RRCSetup by UE" 5GMM Identity (old) 5G-GUTI or SUCI (IMSI or NSI) or PEI 24.501NAS:5.3.2 "Permanent identifiers", 24.501NAS:5.3.3 "Temporary identities", 23.003NAS:2.2B "SUCI", 23.003NAS:6.4 "PEI" Above Access Stratum "machine", consisting of PDCCH, PDSCH, PUSCH, and PUCCH continue to operate and it is not shown in the rest of the message sequence for simplicity. UL RRC MESSAGE TRANSFER [RRC Setup Complete] 38.473F1:8.4.3 "UL RRC Message Transfer" INITIAL UE MESSAGE [5GMM REGISTRATION REQUEST] 38.413NG:8.6.1 "Initial UE message" AMF may do (optional) identity procedure before triggering authentication procedure.It is not shown here. 24.501NAS:5.4.3 "Identification procedure" Nausf UEAuthentication Authenticate Request (SUCI) AUSF and UDM interaction is not covered here. 33.501NGC:6.1.2 "Initiation of authentication and selection of authentication method" Nausf UEAuthentication Authenticate Response 33.501NGC:6.1.3.2 "Authentication procedure for 5G AKA" DL NAS Transport [5GMM AUTHENTICATION REQUEST] 24.501NAS:5.4.1 "Primary authentication and key agreement procedure", 38.413NG:8.6.2 "DL NAS transport" DL RRC MESSAGE TRANSFER [RRC DL Information Transfer] RRC DL Information Transfer [5GMM AUTHENTICATION REQUEST] 38.331RRC:5.7.1 "DL information transfer" UICC Authenticate 31.102USIM:5.2.1 "Authentication algorithms computation" RRC UL Information Transfer [5GMM AUTHENTICATION RESPONSE] 38.331RRC:5.7.2 "UL information transfer" UL RRC MESSAGE TRANSFER [RRC UL Information Transfer] UL NAS Transport [5GMM AUTHENTICATION RESPONSE] 38.413NG:8.6.3 "UL NAS transport" Nausf UEAuthentication Authenticate Request (SRES) Nausf UEAuthentication Authenticate Response As seen above, F1AP provides transport for RRC messages.In turn, RRC, F1AP, and NGAP provides transport for NAS messages.Transport messages are not shown in the rest of the message sequence for simplicity. 5GMM SECURITY MODE COMMAND 24.501NAS:5.4.2 "Security mode control procedure" 5GMM SECURITY MODE COMPLETE AMF and UDM interaction is not covered here (these interactions are similar to interactions between MME and HSS in LTE e.g. location update). 29.503UDM "UDM services" INITIAL CONTEXT SETUP REQUEST [5GMM REGISTRATION ACCEPT] 38.413NG:8.3.1 "Initial Context Setup" UE CONTEXT SETUP REQUEST [RRC Security Mode Command] 38.473F1:8.3.1 "UE Context Setup", 38.331RRC:5.3.4 "Initial AS security activation" RRC Security Mode Command UE CONTEXT SETUP RESPONSE RRC Security Mode Complete UE Capability Enquiry 38.331RRC:5.6.1 "UE capability transfer" UE Capability Information RRC Reconfiguration [5GMM REGISTRATION ACCEPT] 38.331RRC:5.3.5 "RRC reconfiguration" Got updated cell configuration (spCellConfigDedicated) (possibly based on UE capability) RRC Reconfiguration Complete INITIAL CONTEXT SETUP RESPONSE 5GMM-REGISTERED 5GMM Identity new 5G-GUTI or keep the same as old one 5GMM REGISTRATION COMPLETE 5GSM triggers PDU Session Establisment 24.501NAS:6.4.1 "UE-requested PDU session establishment procedure" 5GMM UL NAS TRANSPORT [5GSM PDU SESSION ESTABLISHMENT REQUEST] 24.501NAS:5.4.5.2 "UE-initiated NAS transport procedure" Nsmf PDUSession CreateSMContext Request [5GSM PDU SESSION ESTABLISHMENT REQUEST] 29.502N11:5.2.2.2 "Create SM Context service operation" Nsmf PDUSession CreateSMContext Response N4 Session Establishment Request 23.502NGC:4.4.1.2 "N4 Session Establishment procedure" UPF's interaction with PDN (usually IP based) is not covered here. PDU Session to NG-U/GTP-U Tunnel mapping from UPF side 38.300RAN:12 "QoS" N4 Session Establishment Response Namf Communication N1N2MessageTransfer [5GSM PDU SESSION ESTABLISHMENT ACCEPT] PDU SESSION RESOURCE SETUP REQUEST [5GSM PDU SESSION ESTABLISHMENT ACCEPT] 38.413NGC:8.2.1 "PDU Session Resource Setup" BEARER CONTEXT SETUP REQUEST 38.463E1:8.3.1 "Bearer Context Setup" BEARER CONTEXT SETUP RESPONSE PDU Session to NG-U/GTP-U Tunnel mapping from gNB CU UP side PDU Session to DRB and DRB to QoS flow (5QI) mapping One PDU Session may have more than one DRB and one DRB may have more than one QoS flow 38.300RAN:12 "QoS" UE CONTEXT MODIFICATION REQUEST [RRC Reconfiguration [5GSM PDU SESSION ESTABLISHMENT ACCEPT]] 38.473F1:8.3.4 "UE Context Modification (gNB-CU initiated)" RRC Reconfiguration [5GSM PDU SESSION ESTABLISHMENT ACCEPT] Got SRB2 and PDU session + DRB configuration Downlink PDSCH mapped to DL-SCH mapped to CCCH (SRB2) Uplink DCCH (SRB2) mapped to UL-SCH mapped to PUSCH Downlink PDSCH mapped to DL-SCH mapped to DTCH (DRB) Uplink DTCH (DRB) mapped to UL-SCH mapped to PUSCH Got information about PDU Session and QoS flows 23.501NAS:5.7 "QoS model" 5GSM-PDU-SESSION-ACTIVE RRC Reconfiguration Complete UE CONTEXT MODIFICATION RESPONSE BEARER CONTEXT MODIFICATION REQUEST 38.463E1:8.3.2 "Bearer Context Modification (gNB-CU-CP initiated)" BEARER CONTEXT MODIFICATION RESPONSE PDU SESSION RESOURCE SETUP RESPONSE Nsmf PDUSession UpdateSMContext Request 29.502N11:5.2.2.3 "Update SM Context service operation" N4 Session Modification Request 23.502NGC:4.4.1.3 "N4 Session Modification procedure" UPF now knows NG-U/GTP-U tunnel ID from gNB CU UP side N4 Session Modification Response Nsmf PDUSession UpdateSMContext Response DL data starts from UPF DL data transfer IP packet NG-U over GTP-U F1-U over GTP-U PDSCH UL data transfer PUSCH F1-U over GTP-U NG-U over GTP-U IP packet

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