Section: 4.3.2.1 Charging Trigger Function
Content: 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 4.2.1 for information on the applicability of CAP or Ro per NE type.