4 Architecture considerations
32.2513GPPCharging managementPacket Switched (PS) domain chargingRelease 17Telecommunication managementTS
4.0 General
This clause describes the functional entities involved in the PS domain charging architecture. It also presents the mappings of the ubiquitous offline and online charging architecture specified in TS 32.240 [1] onto physical implementations that are standardized for the 3GPP PS domain.
4.1 High-level EPS architecture
The 3GPP PS domain provides procedures for packet core networks described in TS 23.060 [201], TS 23.401 [208],
TS 23.402 [209] and TS 23.272 [213].
For offline charging the following Packet switched Core network Nodes (PCN) may generate accounting metrics sets for PS domain CDRs:
– the SGSN, to record a user’s access to PLMN resources, mobility management activities, SMS and LCS usage;
– the S-GW, to record a user’s access to PLMN resources;
– the ePDG, to record a user’s access to PLMN resources;
– the TWAG, to record a user’s access to PLMN resources (optional) ;
– the P-GW, to record a user’s access to external networks ;
– the GGSN, to record a user’s access to external networks;
– the MME, to record a user’s SMS;
– the TDF, to record a user’s access to external networks and applications.
The PCNs send the CDRs to the CGF in near real-time. The responsibility of the CGF is to provide non-volatile CDR storage and the Bp interface towards the Billing Domain (BD). Further details on the CGF can be found in TS 32.240 [1] and TS 32.297 [52].
For more information about online charging in PS domains see clause 4.3.
When P-GW provides connectivity to GERAN/UTRAN (P-GW acts as a GGSN) it employs P-GW charging defined in this specification. When the stand-alone GGSN provides connectivity to GERAN/UTRAN, it employs P-GW charging as defined in the present document:
– Stand-alone GGSN offline charging is based on FBC IP-CAN bearer charging data in P-GW;
– Stand-alone GGSN online charging is based on PS Information used for online charging.
4.2 PS domain offline charging architecture
As described in TS 32.240 [1], the CTF (an integrated component in each charging relevant NE) generates charging events and forwards them to the CDF. The CDF, in turn, generates CDRs which are then transferred to the CGF.
Finally, the CGF creates CDR files and forwards them to the BD.
If the PCN generating the charging information has an integrated CDF, then the PCN can produce CDRs. The CGF may also be integrated in the PCN, or it may exist as a physically separate entity.
If the CGF is external to the PCN, then the CDF forwards the CDRs to the CGF across the Ga interface.
In this case, the relationship between PCN/CDF and CGF is m:1.
If the CGF is integrated in the PCN, then there is only an internal interface between the CDF and the CGF.
In this case, the relationship between PCN/CDF and CGF is 1:1. An integrated CGF may support the Ga interface from other PCN/CDFs.
If the CDF is external to the PCN, the charging events are transferred from the PCN to the CDF via the Rf interface specified in TS 32.299 [50]. In this case, the relationship between PCN and CDF is m:1.
When an external CGF is used, this CGF may also be used by other, i.e. non-PS, network elements, according to network design and operator decision. It should be noted that the CGF may also be an integrated component of the BD – in this case, the Bp interface does not exist and is replaced by a proprietary solution internal to the BD.
Figure 4.2.1 depicts the architectural options described above.
Bp
PS Domain
PCN
BS
Bp
PCN
CGF
Ga
Bp
PCN
CGF
Ga
CDF/CGF
CDF
CDF
Billing
Domain
PCN
CDF
CGF
Ga
Bp
CTF
CDF/CGF
Rf
PCN
Figure 4.2.1: PS domain offline charging architecture
The P-GW includes a Policy and Charging Enforcement Function (PCEF) to support Flow Based bearer Charging (FBC) functionality; this is not depicted in figure 4.2.1. The Traffic Detection Function (TDF) supports Application Based Charging (ABC) functionality. The Rf, Ga and Bp interfaces include the required functionality, e.g. defined for the Gz/Gzn reference point in TS 23.203 [215]. Refer to clause 5.2.1.3, TS 32.240 [1] and TS 23.203 [215] for further details on FBC.
The PCNs may provide inter-operator charging functionality for Multimedia Broadcast/Multicast Services (MBMS) defined in TS 23.246 [207] and TS 32.273 [33], not for subscriber charging.
It is mandatory to support at least one of the options Rf, Ga or Bp interfaces from the PCN as described in the specification.
NOTE: The Rf interface details are specified for S-GW, ePDG, TWAG, MME, TDF and P-GW in this release.
4.3 PS domain online charging architecture
PS domain online charging based on SGSN functions is implemented by CAMEL techniques as described in TS 23.078 [206] and TS 29.078 [202], i.e. outside the scope of the 32-series of charging TSs. Note, however, that the CDRs described in the present document contains CAMEL information. This is because some of that information is relevant to offline charging in case of CAMEL control of (part of) the session, and thus needs to be captured in the offline charging information. However, this is not related to the online charging functions for the PS domain.
Mechanisms to enable PS domain online charging from the P-GW with included PCEF and theTDF are specified in the present document, utilising the Ro interface and the associated Diameter application as specified in TS 32.299 [50].
The reason for this alternative solution to CAMEL is that operators may enforce the use of HPLMN P-GWs and TDF in the case of roaming, hence P-GW or TDF service control and charging can be executed in the HPLMN in all circumstances. The P-GW and TDF based PS domain online charging architecture is depicted in figure 4.3.1.
Figure 4.3.1: PS domain online charging architecture
The Ro reference point includes the functionality defined for the Gy reference point (required for the PCEF) and the Gyn reference point (required for the TDF) in TS 23.203 [215]. Refer to clause 5.2.1.3, TS 32.240 [1] and TS 23.203 [215] for further details on FBC.
Details on the interfaces and functions can be found in TS 32.240 [1] for the general architecture components,
TS 32.296 [53] for the OCS, and TS 32.299 [50] for the Ro application.