Question: What is the primary purpose of the Accounting-Request Interim-Update message sent from GGSN/P-GW to AAA server in a PLMN supporting packet-based services?
Option 1: To request authentication for a new user
Option 2: To update the accounting records for an ongoing session
Option 3: To notify the AAA server of a change in the user's location
Option 4: To provide interim usage information for billing and charging purposes
Explanation: The Accounting-Request Interim-Update message is used to provide interim usage information, such as volume of data transferred or duration of session, to support billing and charging processes. This allows the AAA server to keep track of the user's usage in real-time, enabling accurate billing and charging.