Question: In a 3GPP system, what type of charging data recording is mandatory for control plane transfer of small data messages in IoT scenarios?
Option 1: Online charging with real-time credit control
Option 2: Offline charging with periodic billing cycles
Option 3: Both online and offline charging depending on UE configuration
Option 4: Offline charging for all control plane small data message transfers
Explanation: For IoT resource efficiency, especially in scenarios involving small data transmissions, the 3GPP system is required to optimize its operations. Given the nature of control plane transfers, which are typically signaling-related and not continuously generating large volumes of data, offline charging (where charging information is collected and processed in batches) is more suitable for such low-volume, high-frequency transactions. This approach aligns with the need for resource efficiency in IoT deployments, making Option 4 the correct answer as it specifically addresses the requirement for control plane transfers of small data messages.