Question: What is the primary focus of the X2 Application Protocol (X2AP) in the context of Evolved Universal Terrestrial Radio Access Network (E-UTRAN)?
Option 1: User Plane Data Transfer between eNBs and Core Network Elements
Option 2: Management of UE Subscription Profiles across Different Networks
Option 3: Radio Network Layer Signalling Procedures for Control Plane between eNBs
Option 4: Configuration of QoS Parameters for End-to-End IP Connectivity
Explanation: The X2 Application Protocol (X2AP) is crucial for communication between eNodeBs (eNBs) in E-UTRAN, focusing on control plane aspects. Its primary role is to specify signalling procedures at the radio network layer, ensuring efficient control and management of resources, handovers, and interference mitigation directly between eNBs, facilitating seamless mobility and optimized network performance.