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5GS – UE‑Triggered Service Request – 10 of 36
Signalling flow for TS 23.502 UE-Triggered Service Request: UPF (PSA) to SMF - N4 Session Modification Response message

Step 7b, verbatim
The UPF (PSA) sends N4 Session Modification Response message to SMF.
If the Data Forwarding Indication is received, the UPF (PSA) becomes as N3 Terminating Point and sends CN DL tunnel info for the old (intermediate) UPF to the SMF. The SMF starts a timer, to be used in step 20a to release the resource in old intermediate UPF if there is one.
If the N3 UPF is the UPF (PSA), and if the SMF finds that the PDU Session is activated when receiving the Nsmf_PDUSession_UpdateSMContext Request in step 4 with Cause set to indicate "establishment of user plane resources" for the PDU Session(s), it deletes the RAN tunnel info and initiates an N4 Session Modification procedure to remove Tunnel Info of AN in the UPF.