[Conditional] SMF to UPF (PSA): N4 Session Modification Request.
Depending on the network deployment, the CN Tunnel Info of UPF (PSA) allocated for N3 or N9 interface may be changed during the Service Request procedure, e.g. UPF connected to different IP domains. If the different CN Tunnel Info need be used, and the CN tunnel info is allocated by the UPF, the SMF sends N4 Session Modification Request message to UPF (PSA). If the CN Tunnel Info is allocated by the SMF, the SMF may provide updated CN tunnel info and UL Packet detection rules in step 7 instead.