Offline Charging System

Featuring a Charging Data Function (CDF), a Charging Gateway Function (CGF) and a Billing Function (BF) emulating a Billing System as well as extensions to the PCRF and the PDN GW for the differentiation of bearers for charging, the OpenEPC Offline Charging System enables flexible models of billing as well as an extended GUI for enabling the showcasing of the correlation opportunities. The implementation is based on the 3GPP TS 32.240 specification as well as on the OpenEPC DIAMETER stack implementation.

The OpenEPC Offline Charging System is fully integrated with the Fraunhofer FOKUS Open IMS Core as well as with the FOKUS Broker and other applications servers. Based on customer requirements, specific configurations can be deployed for the testbed services and applications.

Charging Data Function (CDF)

The CDF function has role of gathering data traffic information and generating Call Data Records (CDRs) which are then forwarded to the Charging Gateway Function (CGF) for further processing.

For the information gathering, the CDF uses the Rf interface communication TS 32.299 with an OpenEPC Charging Triggering Function co-located with PDN GW. Additionally the CDF is able to receive information from service platforms such as IMS related to communication sessions accounting as well as from the applications directly enabling application based differentiation towards the billing system.

The CDF support both event and volume based charging which enables complex charging models in which specific bearers are differentially accounted. The event based charging allows scenarios such as billing for whenever a specific content is accessed by a specific subscriber. The volume based charging allows the billing per data or signaling transmitted through the network, differentiated by subscriber, by bearer and correlated with application related information.

CDF functionality includes:

• receiving and processing of charging information from the PDN GW
• receiving and processing of charging information from the service platforms and applications
• Rf interface implementation
• correlation of the received information
• generation of subscriber specific Call Data Records (CDRs)
• sending to CGF the CDRs
• GUI based monitoring of the momentary state of the CDF

Charging Gateway Function (CGF)

The CGF function has as goal the aggregation of the charging information from multiple CDFs as well as from other sources and in other formats and to present this information towards the billing system.

OpenEPC CGF is capable of handling Call Data Records as transmitted by multiple CDFs which are first validated according to the format specified in 3GPP TS 32.298.

Additionally, the CGF may receive information through monitoring of multiple local folders (or remote folders mounted as local) supporting XML format and the ASN.1. The information as ASN.1 may be packaged directly by PDN GWs or GGSNs following the format defined in 3GPP TS 32.298. In OpenEPC, the ASN.1 CDRs are first re-formated in XML format and then are manipulated through the same procedure as the ones received from the CDFs.

CGF functionality includes:

• receiving and processing XML CDRs from multiple CDFs
• receiving and processing ASN.1 CDRs from PDN GWs and GGSNs directly
• DIAMETER based communication interface with the CDF (similar to Rf)
• monitoring for CDRs in local folders
• reading and processing of CDRs from the local folders
• specific CDR parsing and correlation
• correlation of the received information
• generation of subscriber specific billing information
• sending the information to Billing System

Billing Function (BF)

OpenEPC Billing Function (BF) represents a simple and highly flexible Billing System implementation concentrating on the visualization of the CDR information as received from mulitple CGFs. It has the role to aggregate different level CDRs from EPC core network data path, from service platforms and from applications based on common shared information such as IMSI, IMS Charging ID, Access Network Charging Information.

The BF generates and assigns billing entries to subscribers or to service providers. This information can be visualized on a dynamic GUI, easy customizable for the services which are demonstrated on top of the OpenEPC architecture. In the default configuration of the OpenEPC, the BF GUI contains information on the billing associations with different entities such as subscribers and service platforms as well as different bill entries configurable based on a set of administrative controlled rules.

BF functionality includes:

• receiving and processing of CDR information from multiple CGFs
• DIAMETER based communication similar to Rx interface towards the CGF
• correlation of charging information based on specific common shared information
• presentation in a customizable GUI of the bill entries

Other Entities

• PCRF - includes in the bearer establishment, modification and deletion requests send to

• PDN GW information related to the charging identifiers enabling the association between service and bearers. PDN GW - transmits Accounting Requests for the data traffic associated to different subscriber identities including the charging identifier received from the PCRF

• IMS P-CSCF and S-CSCF - The Open Source IMS Core was extended to support the transmission of Accounting Requests related to IMS registrations and session establishment, modification and delete procedures. Additionally, the P-CSCF transmits to the PCRF the IMS Charging Identifier enabling the billing system to correlate the CDR information

• IMS Application Servers - specific Application Servers can be extended on demand to transmit CDRs based on the communication volume or based on application level events.