Registration Procedure Call Flow

This section describes the Registration Procedure call flow.

During the initial registration procedure, the PEI is obtained from the UE. The AMF operator may check the PEI with an EIR. After receiving the PEI (IMEI-SV), the AMF communicates it to the UDM, SMF, and PCF. The UDM stores the PEI in the UDR by sending the Nudr_SDM_Update message.

Registration Procedure Call Flow
Registration Procedure Call Flow Description

Step

Description

1

The UE sends a Registration Request to the RAN.

The Registration Request message includes PEI as part of N2 information. If the PEI is not available, the AMF sends an Identity Request message to retrieve IMEI-SV.

2

The RAN performs the AMF selection procedure.

3

The RAN sends the Registration Request to the T-AMF.

4

The T-AMF sends a UeContextTransferRequest to the S-AMF.

5

The S-AMF responds to the AMF with UeContextTransferResponse.

6

The T-AMF sends the Identity Request message to the UE.

7

The UE sends the Identity Response message to the T-AMF.

8

The T-AMF performs the AUSF selection procedure.

9

The T-AMF sends the Authentication or Security message to the UE.

10

The T-AMF sends the RegistrationStatusUpdate message to the S-AMF.

11

The T-AMF sends the Identity Request or Response (PEI) message to the UE.

The AMF initiates the Identity Request procedure by sending an Identity Request message to the UE to retrieve the PEI when:

  • The UE does not provide the PEI.

  • The UE cannot retrieve the PEI from the old AMF.

The AMF transfers an encrypted PEI unless the UE performs an Emergency Registration. For Emergency Registration, the UE includes the PEI in the Registration Request so that the PEI retrieval step is skipped.