Understanding Policy and Charging Enforcement Function (PCEF)
The policy and charging enforcement function (PCEF) of the Service Control Gateway enforces policy decisions that are specified by policy and charging control (PCC) rules for the treatment of subscriber packets. A PCC rule is installed on, and enforced by, the Service Control Gateway PCEF. The PCC rules can be under static control, under dynamic control of the policy and charging rules function (PCRF), or under activation/deactivation control of a RADIUS server, depending on the PCEF profile that is assigned to a Service Control Gateway subscriber.
Static Policy Control
For static policies, the PCEF enforces PCC rules that are predefined on the Service Control Gateway with no interaction from the PCRF or a RADIUS server, as shown in Figure 1.
Dynamic Policy Control
For dynamic policies, the PCEF acts upon messages received from the PCRF. The PCRF is the central entity that makes policy and charging decisions based on input from different sources, such as mobile operator configuration, user subscription information, and services information. The PCC rules are either provisioned by the PCRF and sent to the PCEF over the Gx interface using Diameter AVPs, or the PCC rule is predefined on the Service Control Gateway and the PCRF sends a Diameter message to activate that rule. The PCEF also provides the PCRF with subscriber and access information. See Figure 2.
When PCC rules are under dynamic control, the PCEF gives precedence to rules sent by the PCRF over rules that are predefined on the PCEF.
RADIUS Server Policy Control
For polices under control of a RADIUS server, a RADIUS server activates and deactivates policy and PCC rules that you have predefined on the Service Control Gateway, as shown in Figure 3.