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5GS – UE‑Triggered Service Request – 06 of 36
Signalling flow for TS 23.502 UE-Triggered Service Request: UPF selection

Step 5, verbatim
If the PDU Session ID corresponds to a LADN and the SMF determines that the UE is outside the area of availability of the LADN based on the UE location change notification from the AMF, the SMF decides to (based on local policies) either:
keep the PDU Session, but rejects the activation of user plane connection for the PDU Session and informs the AMF about it. If the procedure has been triggered by a Network Triggered Service Request as described in clause, the SMF may notify the UPF that originated the Data Notification to discard downlink data for the PDU Sessions and/or to not provide further Data Notification messages; or
to release the PDU Session: the SMF releases the PDU Session and informs the AMF that the PDU Session is released.
In any case of the two cases above the SMF answers to the AMF (step10) with an appropriate reject cause and the User Plane Activation of PDU Session is stopped.
Otherwise, based on the location info received from the AMF, the SMF checks the UPF Selection Criteria according to clause 6.3.3 of TS 23.501 [2], and determines to perform one of the following:
accepts the activation of UP connection and continue using the current UPF(s);
accepts the activation of UP connection and selects a new intermediate UPF (or add/remove an intermediate UPF), if the UE has moved out of the service area of the UPF that was previously connecting to the AN, while maintaining the UPF(s) acting as PDU Session Anchor. The steps to perform I-UPF addition/change/removal are described as conditional steps in the following of the current procedure; or
NOTE 1: If the old and/or new I-UPF implements an UL CL or BP functionality and a PDU Session Anchor for connectivity to the local access to the Data Network as described in TS 23.501 [2] clause, the signalling described in the current clause is intended as the signalling to add, remove or change the PDU Session Anchor, and must be complemented by the signalling to add, release or change the UL CL or BP as described respectively in clauses, and
rejects the activation of UP connection of a PDU Session of SSC mode 2, and trigger re-establishment of the PDU Session after Service Request procedure to perform the allocation of a new UPF to act as PDU Session Anchor, e.g. the UE has moved out of the service area of the anchor UPF which is connecting to RAN.