How it Works
The Gx support for SMF uses the following two main elements in the PCC architecture.
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PCEF (Policy enforcement functionality within SMF)
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PCRF (Policy and charging rules function)
Gx reference point lies between the PCRF and the SMF. The Gx reference point allows the provisioning and removal of PCC rules. The following diagram shows the reference points between various elements involved in the policy infrastructure.

The Gx interface implementation is a part of the diameter connection. The Gx messages commonly involve installing/removing dynamic rules and activating/deactivating predefined rules, and modifying APN-AMBR and Default Bearer QoS.
Associating a rule with a bearer is the task of ‘bearer binding’. The PCEF performs this task in SMF. The binding mechanism is the procedure that associates a service data flow. The flow is defined in a PCC rule by the SDF template to the IP-CAN bearer (deemed to transport the service data flow).
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PCEF bearer binding: The PCEF binds a rule to a bearer. This rule may require to perform a bearer activation or update. The SMF service performs the task of updating or creating a new Bearer. This update happens by invoking the UBR or CBR request towards SGW/MME.
NoteIn the current release, PCEF binding only for default bearer is supported.