Question: What function ensures that a UE has valid subscription at a Closed Subscriber Group (CSG) where it performs an access, specifically for closed mode?
Option 1: CSG Subscription Handling Function
Option 2: Admission and Rate Control Function
Option 3: CSG Charging Function
Option 4: CSG Access Control Function
Explanation: The CSG Access Control Function is responsible for ensuring that a UE has valid subscription at a CSG where it performs an access, specifically for closed mode. This function prevents unauthorized UEs from accessing the CSG cell, thereby maintaining the security and integrity of the network.