Question: What does the 'UE User Plane CIoT Support Indicator' primarily indicate in the context of E-UTRAN?
Option 1: The support for Voice over LTE (VoLTE) services on the User Equipment (UE).
Option 2: Whether User Plane Cellular Internet of Things (CIoT) EPS Optimisation is supported for the UE.
Option 3: The capability of the UE to handle multiple simultaneous S1 connections.
Option 4: The preferred radio access technology (RAT) for the UE when multiple are available.
Explanation: This indicator relates to the support for User Plane CIoT EPS Optimisation on the UE, crucial for efficient IoT service provision over cellular networks, particularly for low-bandwidth, low-power IoT devices.