provides an overview of the online part of the common charging architecture of Figure 188.8.131.52
. The Figure 184.108.40.206.1
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 220.127.116.11
, 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 18.104.22.168
are not completely applicable to the S-CSCF. Clause 22.214.171.124.2
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 126.96.36.199
for information on the applicability of CAP or Ro per NE type.
The following sub-clauses summarise the tasks of the functions comprising the OCS. Details of the OCS, and the role of each of its functional components, are described in TS 32.296
The OCF consists of two distinct modules, namely the Session Based Charging Function (SBCF) and the Event Based Charging Function (EBCF).
The Session Based Charging Function is responsible for online charging of network / user sessions, e.g. voice calls, IP CAN bearers, IP CAN session or IMS sessions.
The Event Based Charging Function performs event-based online charging (also referred to as "content charging"
) in conjunction with any application server or service NE, including SIP application servers.
Online charging in the CS and PS domains may be performed using the CAP reference point from the MSC and SGSN, respectively, to the OCF (refer to TS 23.078
for details on CAP). Online charging communication between the S-CSCF and the SBCF is described in clause 188.8.131.52.2
. All other network elements employ the Ro reference point for online charging (refer to TS 32.299
). Refer to TS 32.296
for details on the relation between the network elements (i.e. the embedded online enhanced CTF) and the SBCF or EBCF, respectively.
As stated above, the S-CSCF does not trigger any online charging events and thus does not include the CTF online charging enhancements described in clause 184.108.40.206
(in contrast, it does have a CTF for offline charging, as described in clause 220.127.116.11
). Instead, the ISC interface is employed by the S-CSCF online charging, implying that online charging is transparent to the S-CSCF and appears like any other service logic controlled by a SIP application server. Therefore, if support for Ro based online charging is required instead of / or in addition to application server or MRFC, a special CTF is needed in order to mediate between the Ro based SBCF and the SIP based service control. This role is taken by the IMS Gateway Function (IMS GWF), which translates between SIP service control towards the S-CSCF and Ro Credit-Control on the OCS side.
From the perspective of the online charging architecture, the IMS GWF is an online charging capable CTF; from the perspective of the S-CSCF, the IMS GWF is a SIP application server and is triggered the same way. It is out of scope of the 3GPP standards whether the IMS GWF is embedded in the S-CSCF, embedded in the OCS/SBCF, or exists as a stand-alone component.
The Rating Function (RF) determines the value of the network resource usage (described in the charging event received by the OCF from the network) on behalf of the OCF. To this end, the OCF furnishes the necessary information, obtained from the charging event, to the RF and receives in return the rating output (monetary or non-monetary units), via the Re reference point. The RF may handle a wide variety of rateable instances, such as:
Rating of data volume (e.g. based on charging initiated by an access network entity, i.e. on the bearer level);
Rating of session / connection time (e.g. based on charging initiated by a SIP application, i.e. on the subsystem level);
Rating of service events (e.g. based on charging of web content or MMS, i.e. on the service level).
The Account Balance Management Function (ABMF) is the location of the subscriber's account balance within the OCS or the CCS. The ABMF is put into functional context within TS 32.296
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 18.104.22.168, 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 22.214.171.124, is employed by the OCS in order to generate / manage CDR files and provide these files to the BD.