12.153GPPGeneral Packet Radio Service (GPRS)GPRS ChargingRelease 1997TS
The following figures 1 and 2 show the GPRS logical architecture and GPRS charging logical architecture.
Figure 1: Overview of the GPRS Logical Architecture
GPRS is logically implemented on the GSM structure through the addition of two network nodes, the Serving GPRS Support Node and the Gateway GPRS Support Node. No inference should be drawn about the physical configuration on an interface from figure 1.
Figure 2: GPRS charging logical architecture
4.1 Charging gateway functionality
The Charging Gateway Functionality (CGF) provides a mechanism to transfer charging information from the SGSN and GGSN nodes to the network operator’s chosen Billing Systems (BS). The Charging Gateway concept enables an operator to have just one logical interface between the CGF and the BS. The CGF may be supported in one of the following ways:
– as a centralised separate network element (Charging Gateway);
– as a distributed functionality resident in the SGSNs and GGSNs.
Support of the centralised or distributed CGF in a network is implementation dependent, and subject to vendor/manufacturer agreement. Regardless of the way in which the CGF is supported in the network, the functionality of the CGF is similar. Figure 3 gives an overview of the two basic configurations: In scenario 1, the GSNs support an external interface to the charging gateways they are connected to. In scenario 2, the GSNs support the charging gateway functionality internally.
Figure 3: Basic architectural scenarios for the CGF location
If the GSNs with internal charging gateway functionality also support the external interface, additional configurations as shown in figure 4 are possible. In scenario 3, the GSN with integrated charging gateway function also acts as CGF for other GSNs. In scenario 4, the GSN with integrated charging gateway function also supports the transmission of CDRs to external CGFs.
Figure 4: Optional scenarios for the CGF configuration
The above four scenarios are not exhaustive.
The CGF provides the mechanism to transfer charging information from the SGSN and GGSN nodes to the network operator’s chosen Billing Systems(s) (BSs). The main functions of the CGF are:-
– the collection of GPRS CDRs from the GPRS nodes generating CDRs
– intermediate CDR storage buffering
– the transfer of the CDR data to the billing systems
The CGF acts as a storage buffer for real time CDR collection. It provides the CDR data to the billing system. The present document identifies the external interfaces of the CGF, but does not specify the internal functionality of the CGF. However, in order to assist in the understanding of the CGF, it may perform specific activities, such as consolidation of CDRs, pre-processing of CDR fields, filtering of unrequired CDR fields, and adding of Operator defined fields for specific billing systems. These specific activities may be performed to optimise the charging information that is to be forwarded to the Billing System, which should reduce the load in the Billing System.
In addition to the centralised CGF it is possible to have the CGF distributed to the SGSNs and/or GGSNs.
The CGF can reside in a separate network element (Charging Gateway) or be integrated in the GSNs. It can receive CDR fields from the GSNs in real time mode. It should have enough storage to enable it to transmit the collected charging data to the Billing System in file mode.
The CGF may have to support several transmission protocols towards the Billing System, depending on the Billing System(s) used. One of the main purposes of the CG (or even just a CGF) is to reduce the number of different interfaces between the billing system (BS) and the GGSNs and SGSNs sending charging data. If a new BS is introduced it must be interfaced to the CGF, i.e. the protocol stacks and configurations of the GSNs do not need not to be updated. The usage and load of mass memory media can be more evenly distributed. The portion of the CGF embedded into a single physical device is called the Charging Gateway entity. The CGF may be distributed to several physical Charging Gateways or GSNs, to facilitate redundancy. If that Charging Gateway entity that is the Primary Charging Gateway entity, does not respond to communication originating from the GSNs, the GSNs will try to send the CDR data to a Secondary Charging Gateway entity. Here each GSN will have several IP addresses (of different priority) for the Charging Gateway entities, thus avoiding downtime of the CGF.