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1. PDU Session Establishment Request UE->AMF
NAS Message (
S-NSSAI(s),
UE Requested DNN,
PDU Session ID,
Request type,
Old PDU Session ID,
N1 SM container (
PDU Session Establishment Request,
[Port Management Information Container]
)
).
-> UE will generate a new PDU session ID to start a new PDU session.
-> UE will send this request by transmitting a NAS message containing a PDU session establishment request within the N1 SM container.
-> If the Request Type indicates “Initial request”, then it is a new PDU session, else if it indicates “Existing PDU Session”.
2. SMF Selection
-> The AMF selects an SMF as described in clause 6.3.2 of TS 23.501 and clause 4.3.2.2.3.
-> If the AMF cannot select an SMF, the AMF shall reject the PDU session establishment request with an appropriate reason
-> If the request type is “Existing PDU Session”, the AMF selects the SMF from the UDM based on the SMF-ID.
3. Nsmf_PDUSession_CreateSMContext Request AMF->SMF
-> AMF invokes the Nsmf_PDUSession_CreateSMContext Request, if the AMF does not have an association with an SMF for the PDU Session ID provided by the UE.
-> AMF invokes the Nsmf_PDUSession_UpdateSMContext Request, if the AMF already has an association with an SMF for the PDU Session ID provided by the UE
4. Subscription retrieval / Subscription for updates
-> SMF retrieves the Session Management Subscription data using Nudm_SDM_Get (SUPI, Session Management Subscription data, selected DNN, S-NSSAI of the HPLMN, Serving PLMN ID, [NID])
5. Nsmf_PDUSession_CreateSMContext Response SMF->AMF
-> Nsmf_PDUSession_CreateSMContext Response or an Nsmf_PDUSession_UpdateSMContext Response depending on the request received in step 3.
6. PDU Session authentication/authorization optional
-> If “Existing PDU Session”, then SMF will not do secondary authentication/authorization.
7a. PCF selection
-> If dynamic PCC is to be used for the PDU Session, the SMF performs PCF selection
7b. SM Policy Association Establishment / SMF initiated SM Policy Association Modification
-> SMF performs an SM Policy Association establishment process, as defined in Section 4.16.4
8. UPF selection
-> SMF performs selection or re-selection of UPF, depending on the deployment scenario of UPF, such as centralized deployment, distributed deployment of UPF close to the point of entry.
9. SMF initiated SM Policy Association Modification
-> SMF may perform an SMF initiated SM Policy Association Modification procedure as defined in clause 4.16.5.1 to provide information on the Policy Control Request Trigger condition(s) that have been met.
10a. N4 Session Establishment/Modification Request
-> If Request Type indicates “initial request”, the SMF initiates an N4 Session Establishment procedure with the selected UPF.
10b/10c. N4 Session Establishment/Modification Response
-> The SMF sends an N4 Session Establishment/Modification Request to the UPF and provides Packet detection, enforcement and reporting rules to be installed on the UPF for this PDU Session.
11. Namf_Communication_N1N2MessageTransfer SMF->AMF
-> SMF will send AMF Namf_Communication_N1N2MessageTransfer, that will have PDU Session ID, N2 SM information , N1 SM container.
12. N2 PDU Session Request(NAS msg) AMF->(R)RAN
-> N2 PDU Session Request (N2 SM information, NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept)), [CN assisted RAN parameters tuning]). I
13. AN-Specific resource setup(R)AN->UE
-> The (R)AN may issue AN specific signalling exchange with the UE that is related with the information received from SMF.
14. N2 PDU Session Response (R)AN->AMF
-> 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)).
15. Nsmf_PDUSession_UpdateSMContext Request AMF->SMF
-> Nsmf_PDUSession_UpdateSMContext Request (SM Context ID, N2 SM information, Request Type).
-> The AMF forwards the N2 SM information received from (R)AN to the SMF.
16a. N4 Session Modification Request SMF->UPF
-> The SMF initiates an N4 Session Modification procedure with the UPF.
16b. N4 Session Modification Response UPF->SMF
-> The UPF provides an N4 Session Modification Response to the SMF.
16c. Registration
-> If the SMF has not yet registered for this PDU Session, then the SMF registers with the UDM using Nudm_UECM_Registration (SUPI, DNN, S-NSSAI, PDU Session ID, SMF Identity, Serving PLMN ID, [NID]) for a given PDU Session.
17. Nsmf_PDUSession_UpdateSMContext Response SMF->AMF
-> SMF subscribes UE mobility event notifications from AMF (eg location report, UE moves into or out of area)
18. [Conditional] Nsmf_PDUSession_SMContextStatusNotify (Release) SMF to AMF
-> If during the procedure, any time after step 5, the PDU Session establishment is not successful, the SMF informs the AMF by invoking Nsmf_PDUSession_SMContextStatusNotify (Release).
19. IPv6 Address Configuration SMF->UE
-> In the case of PDU Session Type IPv6 or IPv4v6, the SMF generates an IPv6 Router Advertisement and sends it to the UE.
20. SMF initiates SM Policy Association Modification
21. UnSubscription
-> If the PDU Session establishment failed, SMF will unsubscribe using Nudm_SDM_Unsubscribe.
Source TS 23.502