5G : PDU Session Establishment
#5G #NGC #SA #NSA #telecom #telecommunications
For user plane connection, PDU Session establishment is required and may correspond to the:
- a UE initiated PDU Session Establishment procedure (depicted below)
- a UE initiated PDU Session handover from EPS to 5GS.
- a Network triggered PDU Session Establishment procedure.
1. From UE to AMF: NAS Message (contains S-NSSAI(s), PDU Session ID, Request type, Old PDU Session ID, N1 SM container (PDU Session Establishment Request)). In order to establish a new PDU Session, the UE generates a new PDU Session ID.
2. The AMF determines that the message corresponds to a request for a new PDU Session based on that Request Type indicates “initial request”
3. From AMF to SMF: Nsmf_PDUSession_CreateSMContext Request (contains SUPI, S-NSSAI(s), PDU Session ID, AMF ID, Request Type, PCF ID, Priority Access, , User location information, Access Type
4. If the SMF has not yet registered for this PDU Session ID, then the SMF registers with the UDM using Nudm_UECM_Registration (SUPI, PDU Session ID) for a given PDU Session.
5. From SMF to AMF: Either Nsmf_PDUSession_CreateSMContext Response (Cause, SM Context ID or N1 SM container (PDU Session Reject (Cause)) or an Nsmf_PDUSession_UpdateSMContext Response depending on the request received in step 3.
6. The SMF selects one or more UPFs. In the case of PDU Session Type IPv4 or IPv6 or IPv4v6, the SMF allocates an IP address/prefix for the PDU Session.
7. 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.
8. The UPF acknowledges by sending an N4 Session Establishment or Modification Response.
9. SMF to AMF: Namf_Communication_N1N2MessageTransfer (PDU Session ID, N2 SM information (PDU Session ID, QFI(s), QoS Profile(s), CN Tunnel Info, S-NSSAI from the Allowed NSSAI, Session-AMBR, PDU Session Type, User Plane Security Enforcement information, UE Integrity Protection Maximum Data Rate)
10. AMF to (R)AN: N2 PDU Session Request (N2 SM information, NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept))).
11. (R)AN to UE: The (R)AN may issue AN-specific signalling exchange with the UE that is related with the information received from SMF.
12. (R)AN to 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))
13. Uplink data started
14. Downlink data started
