PDU Session Establishment with Initial Context Call Flow

This section describes the PDU Session Establishment with Initial Context call flow.

PDU Session Establishment with Initial Context Call Flow
PDU Session Establishment for Existing PDU Call Flow Description

Step

Description

1

In order to establish a new PDU Session, the UE generates a new PDU Session ID and initiates the PDU Session Establishment procedure by the transmission of a NAS message containing a PDU Session Establishment Request within the N1 SM container. The PDU Session Establishment Request includes the following:

  • PDU session ID

  • Requested PDU Session Type

  • Requested SSC mode

  • 5GSM Capability PCO

  • SM PDU DN Request Container

  • Number of Packet Filters

2,3,4

If the PDU exists, then clean up at AMF and SMF (SmContextReleaseRequest) is done and PDU establishment is performed.

5, 6

The AMF selects SMF based on slice-info and plmn-info provided by UE. SMF is selected by NRF query or by static configuration. The AMF invokes the Nsmf_PDUSession_CreateSMContext Request towards SMF with SUPI, DNN, S-NSSAIs, PDU Session ID, AMF ID, Request Type, PCF ID, Priority Access, N1 SM container (PDU Session Establishment Request), User location information, Access Type, PEI, GPSI, UE presence in LADN service area, Subscription For PDU Session Status Notification, DNN Selection Mode. Subscriber data-store is modified to store PDU information. The AMF service stickiness is maintained for the subscriber for the PDU establishment transaction.

The SMF creates an SM context and responds to the AMF by sending Nsmf_PDUSession_CreateSMContext Response (Cause, SM Context ID or N1 SM container (PDU Session Reject (Cause)).

The SMF sends Namf_Communication_N1N2MessageTransfer to the AMF. The N2 SM information carries information that the AMF forwards to the RAN. The N1 SM container contains the PDU Session Establishment Accept that the AMF provides to the UE. The Namf_Communication_N1N2MessageTransfer contains the PDU Session ID allowing the AMF to know which access towards the UE to use.

The SMF receives Namf_Communication_N1N2MessageTransfer response from the AMF.

7

The gNB sends the Initial Context Setup Request to the AMF.

The RAN forwards the NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept)) to the UE.

8

The AMF responds with the Initial Context Setup Response to the gNB.

The response includes the N2 PDU Session Response (PDU Session ID, Cause, N2 SM information (PDU Session ID, AN Tunnel Info, List of accepted/rejected QFI(s), User Plane Enforcement Policy Notification)).

9

The AMF sends Nsmf_PDUSession_UpdateSMContext Request to the SMF

The Nsmf_PDUSession_UpdateSMContext Request includes the N2 SM information and Request Type. The AMF forwards the N2 SM information received from RAN to the SMF.

10

The SMF sends the Nsmf_PDUSession_UpdateSMContext Response to the AMF.