Question: What is the primary function of Inter-PLMN UP Security (IPUPS) in the 5G System architecture?
Option 1: To enforce GTP-U security on the N9 interface between UPFs of different PLMNs.
Option 2: To protect control plane messages between the UE and the gNB.
Option 3: To secure the communication between the AMF and the SMF.
Option 4: To authenticate users before granting access to the network.
Explanation: IPUPS is a functionality of the UPF that enforces GTP-U security on the N9 interface between UPFs of different PLMNs, protecting user plane messages at the perimeter of the PLMN.