Initial Registration Call Flow

This section describes the Initial Registration call flow.

Initial Registration Call Flow
Initial Registration Call Flow Description

Step

Description

1

The UE sends Registration Request to the AMF.

2

The authentication procedure occurs between the UE and the AMF.

3

The AMF performs the equipment status check with the EIR using the GET command.

4

The AMF receives 200 OK from the EIR.

5

The AMF requests the Access and Mobility subscription from the UDM.

The UDM responds to the AMF request and the AMF stores the subscription information for RAT and core network type in UeContext.

6

The AMF receives 200 OK from the UDM.

7

The AMF requests the SMF selection subscription data from the UDM.

8

The AMF receives 200 OK from the UDM.

9

The AMF requests the UDM for the notifications when data is modified.

10

The UDM registers the AMF and responds to the AMF for subscription with 201.

11

The AMF selects the PCF based on PLMN, slice information, and performs Policy Association Establishment.

The PCF sends the policy data to the AMF with restrictions and other policies to be applied for the UE.

12

The PCF responds to the AMF request along with am-policy configurations for the subscriber.

13

The AMF sends Registration Accept to the UE in Initial Context Setup Downlink NAS TPT indicating that Registration Request is accepted.

The AMF fills in the Mobility Restriction List IE with RAT and core restrictions as per the UDM or local configuration settings.

Registration Accept contains the following:

  • 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 gNB sends Initial Context Setup Response to the AMF.

15

When a new 5G-GUTI is included in Registration Accept, the UE sends Registration Complete to the AMF in Uplink NAS TPT. This message acknowledges that a new 5G-GUTI is assigned.

16

If the UE doesn't include a follow-on indication in the request:

  • The AMF sends UE Context Release Command to the gNB.

  • AMF releases the UE.

17

The gNB responds with UE Context Release Complete to the AMF.