Question: What is the primary purpose of the Serial Number parameter in an ETWS (Earthquake and Tsunami Warning System) Primary Notification message, as per 3GPP standards?
Option 1: To identify the source of the warning, distinguishing between different alert initiators.
Option 2: To track changes to the ETWS Primary Notification message when its content is updated for a given Message Identifier.
Option 3: To provide a unique identifier for every recipient device (UE: User Equipment) receiving the alert.
Option 4: To specify the priority level of the warning, influencing how quickly it must be displayed by the UE.
Explanation: The correct answer is Option 2 because the Serial Number parameter is specifically altered every time the content of an ETWS Primary Notification message (identified by a given Message Identifier) is changed. This ensures that updates to alerts can be identified and processed correctly by receiving devices, highlighting its role in version control for alert messages rather than source identification, recipient tracking, or priority signaling.