Question: Under what condition(s) will a Traffic Detection Function (TDF) stop time measurement for a Monitoring Key if no packets are received, assuming an Inactivity Detection Time value is provided?
Option 1: Immediately after the Inactivity Detection Time expires, regardless of subsequent packet arrivals.
Option 2: After the Inactivity Detection Time interval, but only if no packets belonging to the Monitoring Key are received; measurement resumes with the next packet arrival.
Option 3: When usage monitoring is explicitly disabled by the Policy and Charging Rules Function (PCRF), without considering packet arrivals.
Option 4: Upon reaching a predefined volume threshold, irrespective of the Inactivity Detection Time.
Explanation: This option correctly reflects the behavior described for time-based usage monitoring. The TDF stops measuring time after the specified Inactivity Detection Time if no packets are received for the Monitoring Key but resumes measurement upon the arrival of a further packet belonging to that key.