Procedure: Initial Registration

Mirrored documentation

Mirrored read-only from claudia-5gc @ v2.3.1. Edit upstream, not here.

Spec: TS 23.502 §4.2.2.2.2 (UE-initiated initial registration) Status: 🔴 Not implemented (Phase 1 target) Primary NF: AMF Other NFs involved: NRF, AUSF, UDM, UDR, (PCF)

Sequence

sequenceDiagram
  participant UE
  participant gNB
  participant AMF
  participant NRF
  participant AUSF
  participant UDM
  participant UDR
  participant PCF

  UE->>gNB: RRC Setup Request / RRC Setup Complete (NAS: Registration Request)
  gNB->>AMF: NGAP Initial UE Message (RegistrationRequest, SUCI)
  AMF->>NRF: Nnrf_NFDiscovery (target=AUSF)
  NRF-->>AMF: AUSF NFProfile
  AMF->>AUSF: Nausf_UEAuthentication_Authenticate (SUPI/SUCI, ServingNetworkName)
  AUSF->>UDM: Nudm_UEAuthentication_Get (SUCI/SUPI, ServingNetworkName)
  UDM->>UDR: Nudr_DR Query AuthenticationSubscription
  UDR-->>UDM: K, OPC, SQN
  UDM-->>AUSF: 5G HE AV (RAND, AUTN, XRES*, KAUSF)
  AUSF-->>AMF: 5G AV (RAND, AUTN, HXRES*, NgKSI)
  AMF->>UE: NAS Authentication Request (RAND, AUTN, NgKSI)
  UE->>AMF: NAS Authentication Response (RES*)
  AMF->>AUSF: Nausf_UEAuthentication_Authenticate (RES*)
  AUSF-->>AMF: result=true, KSEAF, SUPI
  AMF->>UE: NAS Security Mode Command (NEA/NIA selected)
  UE->>AMF: NAS Security Mode Complete
  AMF->>UDM: Nudm_UECM_Registration (SUPI, AMF instance ID)
  AMF->>UDM: Nudm_SDM_Get (subscription data)
  AMF->>UDM: Nudm_SDM_Subscribe
  AMF->>PCF: Npcf_AMPolicyControl_Create
  PCF-->>AMF: AM Policy
  AMF->>UE: NAS Registration Accept (5G-GUTI, Allowed NSSAI, registration area)
  UE->>AMF: NAS Registration Complete

IEs (key)

• Registration Request: 5GS Registration Type, NgKSI, 5GS Mobile Identity (SUCI/5G-GUTI), UE Security Capability, Requested NSSAI, Last Visited TAI.
• Registration Accept: 5G-GUTI, Equivalent PLMNs, TAI list, Allowed NSSAI, Configured NSSAI, Service Area List, T3512 (periodic update timer).

Error scenarios to test

Scenario	Expected behaviour
Unknown SUPI	Auth Reject; UE deregistered
Mac failure on Authentication Response	Send Auth Failure (Cause: MAC failure); AMF may retry
Synch failure (SQN out of range)	Re-sync via AUTS; UDM updates SQN
Network slice not allowed	Registration Reject (Cause: 5GMM cause #62); Allowed NSSAI = empty
Service Area restrictions	Apply restriction in registration area IE

Timers to validate

• T3502 (UE) — wait time before re-registration after rejection
• T3510 (UE) — Registration Request retransmission
• T3511 (UE) — wait time on temporary failure
• T3512 (UE) — periodic registration update
• T3550 (UE) — Registration Complete retransmission
• T3522 (AMF) — Deregistration Request retransmission
• AMF-side guard timers per implementation

Compliance checklist

• ☐ All IEs encoded per TS 24.501 §8.2 with correct types and lengths
• ☐ SUCI deconcealment via UDM (not in AMF) per TS 33.501 §6.12.2
• ☐ KSEAF derived per TS 33.501 §6.1.3.2
• ☐ NAS security context activated before Registration Accept
• ☐ T3512 sent in Accept; AMF tracks UE periodic update
• ☐ PCF AM Policy retrieval and application
• ☐ UDM subscription so AMF receives data updates