Question: Upon receiving a `Usage-Monitoring-Information` AVP with `Usage-Monitoring-Report` set to `USAGE_MONITORING_REPORT_REQUIRED`, how must the PCEF report accumulated usage if both volume and time thresholds were provided for a specific monitoring key?
Option 1: The PCEF reports only the volume usage, as it is the primary metric for billing.
Option 2: The PCEF reports only the time of usage, since time thresholds indicate session-based charging.
Option 3: The PCEF shall report both the volume usage and time of usage for the specified monitoring key.
Option 4: The PCEF ignores the thresholds and reports usage for all enabled monitoring keys without differentiation.
Explanation: According to the specified procedures, when both volume and time thresholds are provided for a monitoring key, the PCEF is required to report both metrics to ensure comprehensive billing and resource management. This dual reporting allows for flexible charging schemes (e.g., volume-based, time-based, or hybrid) as defined by the PCRF's policies.