Question: What is the primary focus of the 3GPP document regarding the Cx interface in the context of IP Multimedia (IM) Subsystem?
Option 1: Network Architecture and Topology Definitions
Option 2: Functional Requirements, Procedures, and Message Parameters for Communicating Entities
Option 3: Quality of Service (QoS) Management and Policy Control
Option 4: Interoperability Testing Scenarios for Multi-Vendor Environments
Explanation: The correct answer is Option 2 because the document emphasizes functional classification of procedures, describes these procedures, and outlines message parameters specifically for entities communicating over the Cx interface, crucial for seamless interaction within the IP Multimedia Subsystem.