Content for  TS 32.240  Word version:  18.1.0

Figure 4.3.1.0.1 provides an overview of the offline part of the common charging architecture of Figure 4.2.2.1. The Figure 4.3.1.0.1 depicts the logical charging functions as well as the reference points between these functions and to the BD.

The Charging Trigger Function (CTF) generates charging events based on the observation of network resource usage as described in clause 4.1.1. In every network element and service element that provides charging information, the CTF is the focal point for collecting the information pertaining to chargeable events within the network element, assembling this information into matching charging events, and sending these charging events towards the CDF. The CTF is therefore a mandatory, integrated component in all network elements that provide offline charging functionality, as depicted in Figure 4.2.2.1. It is made up of two functional blocks:

• Accounting Metrics Collection
  The process that monitors signalling functions for calls, service events or sessions established by the network users, or the handling of user traffic for these calls, service events or sessions, or service delivery to the user via these calls, service events or sessions. It is required to provide metrics that identify the user and the user's consumption of network resources and/or services in real-time. The exact behaviour and functionality of this process e.g.:
  • trigger conditions for collection of charging information,
  • information elements to collect,
  • which service events, signalling or user traffic to monitor,
  • relationship to services / bearers / sessions,
  depends on functions / services that the NE provides. The Account Metrics Collection can therefore be considered as the network element dependent part of the CTF.
  Depending on implementation choice, NE functions (e.g. the handling of service events or signalling / user traffic) may be distributed among multiple physical "devices" within the NE. In order to be able to capture the required charging information from the service events or signalling / user traffic, the design of the Accounting Metrics Collection has to match the physical design / distribution of these functions within the NE. This implies that in case of such distributed NE functionality, the Accounting Metrics Collection becomes a distributed functionality itself.
• Accounting Data Forwarding
  This process receives the collected accounting metrics and determines the occurrence of chargeable events from a set of one or more of these metrics. It then assembles charging events that match the detected chargeable events, and forwards the charging events towards the CDF via the Rf reference point. The charging events provide information pertinent to the chargeable event, i.e. characterising the network resource usage together with an identification of the involved user(s). There is no assumption of any synchronisation between the reception of individual accounting metrics, however, it must be possible for the Accounting Data Forwarding to complete its overall functionality per charging event in real-time.
  While the exact information received by the Account Data Forwarding from the Account Metrics Collection, and the relevant chargeable events, are specific to each type of network element, the overall functionality of receiving, assembling and forwarding the charging information can be considered generic. Hence the Accounting Data Forwarding is considered the NE independent part of the CTF.

Even when distributed within the network element or service element, the CTF is considered to be part of the network element or service element. In service-specific cases, the CTF functional components of Accounting Metrics Collection and Accounting Data Forwarding are divided between the UE and the network element or service element. This architecture extension, conditionally required for specific services, is specified in Annex D. The behaviour of the CTF with respect to the definition of the chargeable events, the matching charging events and the information elements to collect is specified per domain, subsystem and service in the respective middle tier TS 32.25x, TS 32.26x and TS 32.27x ([10] - [49]).

The Charging Data Function (CDF) receives charging events from the CTF via the Rf reference point. It then uses the information contained in the charging events to construct CDRs. This procedure is characterised by the following conditions:

• CDRs may be constructed from single charging events, i.e. a 1:1 relation between event and CDR.
• CDRs may be constructed from a set of several charging events, i.e. a n:1 relation between event and CDR.
• Each charging event is used for exactly one CDR, i.e. a 1:n relation between event and CDR (with n>1) is not possible.
• Multiple charging events that are used to create a single CDR may not necessarily be of the same type.
• There is no requirement or assumption of any synchronisation between the reception of the charging event(s) and the creation of the resulting CDR. However, the CDF shall be capable of receiving and processing charging events and generating the resulting CDR in near real-time.
• The relationship between CDF and CTF may be 1:1 (integrated CDF) or 1:n (separated CDF) (refer to clause 4.5 for possible physical configurations of the logical charging functions). This includes the possibility of NEs of different types feeding charging events into the same CDF.
• All charging events used to build a CDR must originate from the same NE, i.e. there is no cross-NE or cross-NE-type correlation of charging events in the CDF.

The results of the CDF tasks are CDRs with a well-defined content and format. The content and format of these CDRs are specified per domain / subsystem / service in the related middle tier TS (e.g. TS 32.250 for the CS domain and TS 32.251 for the PS domain, etc,).

The CDRs produced by the CDF are transferred immediately to the Charging Gateway Function (CGF) via the Ga reference point. The CGF acts as a gateway between the 3GPP network and the BD. It uses the Bx reference point for the transfer of CDR files to the BD. The entity relationship between the CDF and the CGF is m:1, i.e. one or more CDFs may feed CDRs into a single CGF. The CGF comprises the following main functions:

• CDR reception from the CDF via the Ga reference point in near real-time. The protocols that may cross the Ga reference point are specified in TS 32.295.
• CDR pre-processing:
  • Validation, Consolidation and (Re-) Formatting of CDRs.
  • CDR error handling.
  • Persistent CDR storage.
• CDR routing and filtering, i.e. storing CDRs on separate files based on filtering criteria such as CDR type, CDR parameters, originating CDF, etc.
• CDR File Management, e.g. file creation, file opening / closure triggers, file deletion.
• CDR file transfer to the BD.

For further details of those functions see TS 32.297.

The Offline Charging System (OFCS) is a grouping of charging functions used for offline charging. It collects and processes charging events from one or more CTFs, and it generates CDRs for subsequent offline downstream billing processes.

Figure 4.3.2.0.1 provides an overview of the online part of the common charging architecture of Figure 4.2.2.1. The Figure 4.3.2.0.1 depicts the logical charging functions in the network and the OCS and the reference points between these functions.

As outlined in clause 4.1.2, online charging is a process where charging information is collected in the network element in the same fashion as in offline charging. This implies that, from the functional perspective, the CTF defined in clause 4.3.1.1, also creates the charging events used for online charging. While the accounting metrics used in online charging are generally the same as in offline charging (i.e. the charging mechanism is transparent to the Accounting Metrics Collection), the following functional enhancements concerning the Accounting Data Forwarding are required in the CTF in order to support online charging:

• The information collected for, and included in, the online charging events is not necessarily identical to the offline charging case (i.e. the chargeable events may not necessarily be identical to those observed in offline charging);
• The charging events are forwarded to the Online Charging Function (OCF) in order to obtain authorisation for the chargeable event / network resource usage requested by the user;
• The CTF must be able to delay the actual resource usage until permission by the OCS has been granted;
• The CTF must be able to track the availability of resource usage permission ("quota supervision") during the network resource usage;
• The CTF must be able to enforce termination of the end user's network resource usage when permission by the OCS is not granted or expires.

The underlying principles for requesting, granting and managing resource usage permissions are described in detail in clause 5.1. Note that the S-CSCF, although involved in online charging, does not create any online charging events, therefore clauses 4.3.2.1 and 4.3.2.2 are not completely applicable to the S-CSCF. Clause 4.3.2.2.2 describes online charging specifically for the S-CSCF. The charging events for online charging are transferred to the OCS using the CAP or Ro reference points. Refer to Figure 4.2.2.1 for information on the applicability of CAP or Ro per NE type.

In offline charging, CDRs are generated in the network and forwarded to the BD for further processing, e.g. generating subscriber bills. In online charging, network resource usage is granted by the OCS based on a subscriber account on the OCS. If required by the operator, CDRs may additionally be generated for online charged subscribers. One way of achieving this is by performing online charging and offline charging simultaneously for these subscribers. Alternatively, the OCS can accomplish this by the use of the appropriate offline charging functions as follows:

• A CDF, as specified in clause 4.3.1.2, is employed by each of the OCFs that are required to generate CDRs from the charging events they receive from the CTF;
• A CGF, as specified in clause 4.3.1.3, is employed by the OCS in order to generate / manage CDR files and provide these files to the BD.

Figure 4.3.3.0.1 provides an overview of converged charging architecture. The Figure 4.3.3.0.1 depicts the logical charging functions in the network and interface between these functions and to the BD. This charging architecture is used for 5G system.

The Charging Trigger Function (CTF) interacts with the Charging Function (CHF) of the Converged Charging System (CCS) using Nchf interface for consuming CHF services as defined in TS 32.290:

• converged charging (Nchf_ConvergedCharging service) wich operates:
• with quota management (online charging);
• without quota management (offline charging);
• offline only charging (Nchf_OfflineOnlyCharging service).

The behaviour of the Charging Trigger Function (CTF) embedded in the service element, sub-system component or Core Network element is specified in the respective middle tier charging specifications.

The Charging Enablement Function (CEF) is a consumer of Nchf charging services, and for the purpose of charging information collection may consume management services, services exposed by other network functions or both.