Question: Which of the following functions is NOT supported by the Gx reference point between the PCEF and PCRF, according to standard telecom practices for Policy and Charging Control?
Option 1: Provision of PCC decision from the PCRF to the PCEF
Option 2: Direct Modification of UE Subscription Data by the PCEF
Option 3: Reporting of the start and stop of detected applications from the PCEF to the PCRF
Option 4: Negotiation of IP-CAN bearer establishment mode (UE-only or UE/NW)
Explanation: The Gx reference point is defined for dynamic control over PCC behavior, including decision provisioning, session management, and reporting. However, direct modification of UE subscription data is not a function attributed to the Gx interface in standard Policy and Charging Control architectures. Such modifications typically involve other interfaces or administrative processes, ensuring separation of concerns and security.