UE Identity Procedure for Unknown Subscribers Call Flow

This section describes the UE Identity Procedure for Unknown Subscribers call flow.

When a Registration Request is received with unknown GUTI then AMF triggers an Identity Request towards UE and requests for an UE identity. Registration proceeds with the new UE identity.

UE Identity Procedure for Unknown Subscribers Call Flow
UE Identity Procedure for Unknown Subscribers Call Flow Description

Step

Description

1

The UE sends the Registration Request with the GUTI to the gNB.

2

During the registration procedure, the AMF determines that the received GUTI is of a subscriber who is not present in AMF. In such case, AMF triggers an identity-request to UE asking for its SUCI.

3

The UE sends the identity-request message to the AMF.

4

The UE responds with its SUCI in the identity-response message to the AMF.

5

The AMF extracts fresh authentication data from the AUSF using the SUCI of subscriber.

6

The AMF sends Authentication Request to the UE to initiate authentication of the UE identity.

7

The UE sends Authentication Response to the AMF to deliver a calculated authentication response to the network. The AMF verifies that the result received and if the result is as expected then the registration procedure is proceeded.

8

The NAS security initiation is started.

9

After the NAS security function is set up, the AMF initiates the NGAP procedure to provide the 5G-AN with security context. The 5G-AN stores the security context and notifies it to the AMF. The 5G-AN uses the security context to protect the messages exchanged with the UE.

10

The AMF selects an UDM based on the PLMN info through the NRF query or static configuration and registers the UE with the UDM using Nudm_UECM_Registration. The UDM stores the AMF identity associated to the Access Type.

11

The AMF retrieves the Access and Mobility Subscription data using Nudm_SDM_Get.

The AMF subscribes to be notified using Nudm_SDM_Subscribe when the data requested is modified.

12

The AMF selects PCF based on PLMN-info and slice-info and performs a Policy Association Establishment. The PCF sends policy data to AMF with restrictions and other policies to be applied for the UE. Currently the policies are not applied for UE and are stored in AMF.

13

The AMF sends a Registration Accept message to the UE indicating that the Registration Request has been accepted. The Registration Accept contains the following:

  • 5G-GUTI

  • Registration Area

  • Mobility restrictions

  • PDU Session status

  • Allowed NSSAI

  • Configured NSSAI for the Serving PLMN

  • Periodic Registration Update timer

  • Emergency Service Support indicator

  • Accepted DRX parameters

14

The UE sends a Registration Complete message to the AMF to acknowledge that a new 5G-GUTI was assigned.