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Understanding Usage Monitoring for TDF Subscribers

 

For TDF subscribers that are assigned to a dynamic policy and charging enforcement function (PCEF) profile, the Service Control Gateway can monitor the subscriber use during a session as a volume of traffic, an amount of time, or both, and send reports to the policy and charging rules function (PCRF) when a threshold is exceeded or when the PCRF requests a report. Data volume and the amount of time used can be tracked for individual or multiple data flows or applications that appear in specific policy and charging control (PCC) rules, or for the entire subscriber session.

This topic includes the following sections:

Tracked Resource Identification

Data usage for a subscriber session is tracked through an object called a monitoring key, which the PCRF configures. Traffic for a particular data flow, application, or combination of data flows and applications can be tracked as a data set by assigning a monitoring key to the PCC rules that identify those flows or applications. For predefined PCC rules, you specify the monitoring key with the PCC rule’s action profile. For dynamic PCC rules, the PCRF specifies the monitoring key for a rule.

Data usage can also be tracked for the entire TDF subscriber session by configuring the monitoring key level as SESSION.

Threshold Configuration

The PCRF specifies a threshold for reporting data usage when it configures a monitoring key. The threshold can be a combination of uplink volume, downlink volume, total volume, and time used. The Service Control Gateway reports the usage information to the PCRF when this limit is exceeded, and resets the volume to zero.

Messages and AVPs That Are Used

The PCRF must first request usage monitoring by sending the Event-Trigger AVP with the value USAGE_REPORT. This request can be sent to the Service Control Gateway in a CCA-I, CCA-U, or RAR message.

The PCRF configures a monitoring key by sending a Usage Monitoring Information (UMI) AVP that includes the following in a CCA-I, CCA-U, or RAR message to the Service Control Gateway:

  • Monitoring-key AVP, which is the identifier.

  • Granted-Service-Unit AVP, which specifies the volume threshold, time threshold, or both.

  • Usage-Monitoring-Level AVP, which indicates whether the monitoring key applies to the entire subscriber session or to particular PCC/ePCC rules.

The PCRF requests usage monitoring for traffic that matches a PCC rule’s data flows or applications by sending the following in a CCA-I, CCA-U, or RAR message to the Service Control Gateway:

  • Charging-Rule-Definition AVP, which identifies the rule.

  • UMI AVP that includes the Monitoring-key AVP, which identifies the monitoring key to which the rule is associated.

The Service Control Gateway reports usage to the PCRF by sending a UMI AVP that includes the following in a CCR-U message:

  • Monitoring-key AVP, which is the identifier.

  • Used-Service-Unit AVP, which gives a combination of uplink volume, downlink volume, total volume, and time used.

The PCRF can request a usage report, regardless of whether the threshold is reached, by sending a UMI AVP that includes the following in a CCA-U or RAR message:

  • Monitoring-key AVP, which is the identifier.

  • Usage-Monitoring-Report AVP, which is set to the value USAGE_MONITORING_REPORT_REQUIRED (0).

The PCRF requests that usage monitoring be disabled for a monitoring key by sending a UMI AVP that includes the following in a CCA-U or RAR message:

  • Monitoring-key AVP, which is the identifier.

  • Usage-Monitoring-Support, which is set to the value USAGE_MONITORING_DISABLED (0).