The Rx reference point, which is based on Diameter, is defined between the PCRF and the AF.
If the AF supports RESTful HTTP and XML, a Protocol Converter (PC) is needed. The interface
between the AF and the PC is named REST-Rx. The REST-Rx interface shall be used in non-IMS scenarios only.
The PC converts the information, received over the REST-Rx interface, into information that can be used on the
Diameter-based Rx interface in order to get an access to the PCC architecture and vice versa. The PC manages RESTful
resources, which are an integral part of the REST-Rx interface.
This interface essentially uses the Accounting-Request (ACR) and Accounting-Answer (ACA) commands defined in RFC 6733 (Diameter), section 9 (Accounting).
In the case of event-based offline charging, when the network element receives the indication that the service has been used/delivered, it sends (acting as a CTF) the charging parameters to the CDF via an EVENT_RECORD ACR.
In the case of session-based offline charging, when the network element receives a service request, it sends (acting as a CTF) a START_RECORD ACR to the CDF, which will open a CDR. At regular interval times (Acct-Interim-Interval proposed by the CDF) the CTF will send an INTERIM_RECORD ACR and the CDF will update the CDR. When the service is terminated, the CTF will send a STOP_RECORD ACR and the CDF will close the CDR.
The information contained in the charging events and the
relevant chargeable events are specific to the domain / subsystem / service and are detailed in the respective middle tier
TSs (see Charging).
This reference point allows applications to create, read, modify and delete any user profile data using the harmonized access interface. The GUP Server locates the data repositories responsible of the storage of the requested profile component(s).
For online charging the Diameter Credit-Control Application (DCCA) defined in RFC 4006 is used.
Three cases for online charging can be distinguished: Immediate Event Charging (IEC), Event Charging with Unit
Reservation (ECUR) and Session Charging with Unit Reservation (SCUR).