1
|
The SMF performs the PDU session establishment procedure as defined in 3GPP TS 23.502.
|
2
|
The UE initiates SIP Registration towards the called-party via UPF, P-CSCF through the backed IMS core network.
|
3
|
P-CSCF sends “Npcf_PolicyAuthorization_Update” to PCF to enforce policies, modify service information, gate control, modify
subscription to SDF notification/deactivation, updating of traffic routing information, and so on (as defined in 3GPP TS 29.514). This service allows the NF consumer to subscribe and unsubscribe the notification of events (for example, change of Access
Type, RAT type, or changes of the PLMN identifier).
|
4
|
The PCF sends Npcf_SMPolicyControl_UpdateNotify request to update and/or delete the PCC rule(s) PDU session-related policy
context at the SMF and Policy Control Request Trigger information. This enforces PCC rules, policy control request triggers,
SDF, and charging related information.
|
5
|
The SMF processes the received PCC rules and sends 200 OK message for a successful scenario. When the processing of any content
fails, the SMF includes "400 Bad Request" in “Npcf_SMPolicyControl_UpdateNotify request” and sends it along with appropriate
cause value as defined in 3GPP TS 29.512.
|
6
|
The SMF sends Namf_Communication_\nN1N2MessageTransfer/Response (PDU Session ID, QFIs, QoS Profile(s), Session-AMBR), N1 SM
container (PDU Session Modification Command (PDU Session ID, QoS rule(s), QoS Flow level parameters if needed for the QoS
Flow(s) associated with the QoS rule(s), QoS rule operation, and QoS Flow level QoS parameters operation, Session-AMBR))).
If the UE is in CM-IDLE state or Mobility handover (HO) state, see the procedure in VoNR MO Call Flow for UE in Idle Mode.
|
7
|
The AMF sends N2 PDU Session Request (N2 SM information received from SMF, NAS message (PDU Session ID, N1 SM container (PDU
Session Modification Command))) message to the (R)AN.
|
8
|
The (R)AN issues AN specific signalling exchange with the UE that is related with the information received from SMF. For example,
in an NG-RAN, an RRC Connection Reconfiguration takes place with the UE modifying the necessary (R)AN resources related to
the PDU session.
|
9
|
The (R)AN acknowledges N2 PDU Session Request by sending a N2 PDU Session ACK (N2 SM information (List of accepted/rejected
QFIs, AN Tunnel Info, PDU Session ID, Secondary RAT usage data), User Location Information) message to the AMF. In case of
Dual Connectivity, if one or more QFIs were added to the PDU session, the primary RAN node assigns one or more of these QFIs
to an NG-RAN node which was not involved in the PDU session earlier. In this case, the AN Tunnel Info includes a new N3 tunnel
endpoint for QFIs assigned to the new NG-RAN node. Correspondingly, if one or more QFIs were removed from the PDU session,
a (R)AN node may no longer be involved in the PDU session anymore, and the corresponding tunnel endpoint is removed from the
AN Tunnel Info. The NG-RAN rejects QFIs if it cannot fulfill the User Plane Security Enforcement information for a corresponding
QoS Profile, for example, due to the UE Integrity Protection Maximum Data Rate being exceeded.
|
10
|
The AMF forwards the N2 SM information and the User Location Information received from the (R)AN to the SMF via Nsmf_PDUSession_UpdateSMContext
service operation.
If the (R)AN rejects QFIs, the SMF updates the QoS rules and QoS parameters if needed for the QoS flow(s) associated with
the QoS rule(s) in the UE accordingly.
|
11
|
The SMF sends an Nsmf_PDUSession_UpdateSMContext Response. N2 SM information includes Secondary RAT Usage Data.
|
12
|
The UE acknowledges the PDU Session Modification Command by sending a NAS message (PDU Session ID, N1 SM container (PDU Session
Modification Command ACK)) message.
|
13
|
The (R)AN forwards the NAS message to the AMF.
|
14
|
The AMF forwards the N1 SM container (PDU Session Modification Command ACK) and User Location Information received from the
(R)AN to the SMF via Nsmf_PDUSession_UpdateSMContext service operation.
|
15
|
The SMF sends an Nsmf_PDUSession_UpdateSMContext Response.
If the SMF-initiated modification is to delete QoS Flows (for example, triggered by PCF) which do not include QoS Flow associated
with the default QoS rule and the SMF does not receive response from the UE, the SMF marks that the status of those QoS Flows is to be synchronized with the UE.
|
16
|
SMF sends ChargingDataUpdateReq by including Multi-Unit-Usage with Rating-Group-Id that are received as part of Charging_Description
of Sm_PolicyControl_UpdateNotify_Request to install PCC Rules.
|
17
|
CHF provides ChargingDataUpdtaeResp with Multi-Unit-Information for received Rating-Group values in requested message. CHF
also provides parameter changes for Session-Level and Rating-Group values.
|
18
|
The SMF updates N4 session of the UPF(s) that are involved in the PDU Session Modification by sending N4 Session Modification
Request (N4 Session ID) message to the PCF. For a PDU Session of Ethernet PDU Session Type, the SMF notifies the PCF to add
or remove Ethernet Packet Filter Set(s) and forwarding rule(s).
The UPFs that are impacted in the PDU Session Modification procedure depend on the modified QoS parameters and the deployment.
For example, in case of the session AMBR of a PDU Session with UL flow classifier (CL) changes, only the UL CL is involved.
|
19
|
The PCF sends an N4 session modification response message containing any information that the PCF has to provide to the SMF
in response to the control information received.
|
20
|
For PCF-initiated policy modification case, the SMF notifies the PCF whether the PCC decision could be enforced or not by
performing an SMF-initiated SM Policy Association Modification procedure as defined in 3GPP TS 23.502, section 4.16.5.1. The SMF notifies any entity that has subscribed to User Location Information related with PDU Session change.
|
21
|
The PCF sends an Npcf_SMPolicyControl_Update response with updated policy information about the PDU session.
|