Section: 5.2.1.1 Transfer of charging events via Rf
Content: In event based charging, a network / user event (e.g. MM submission) corresponds to a single chargeable event. In session based charging, at least two chargeable events are needed, one each to describe the start and the end of the session, respectively. Multiple interim events are possible in order to describe changes to session characteristics (generally termed "change of charging condition", e.g. tariff time switch, change of PDP context QoS or change of IMS session media types), or when certain limits, e.g. time or volume, are exceeded. The CTF transforms each chargeable event into a charging event and forwards these charging events to the CDF in real-time. The relation between chargeable events and charging events is 1:1. For event based charging, the relation between charging events and CDRs is 1:1. For session based charging, the relation between charging events and CDRs is m:n with m >=n. The middle tier TSs specify the chargeable events per domain / service / subsystem even if Rf does not exist as an open interface in the respective domain / service / subsystem, as it is always required to identify the connection between chargeable events and triggers for CDR generation and information addition. If charging events are generated for unsuccessful resource usage attempts, the charging event must describe the reason and the circumstances of the failure. Details, including if and when those events are generated, are specified in the middle tier TSs. Details on the protocol application for the open Rf interface, including the message types and the domain / subsystem /service independent contents of the messages, can be found in TS 32.299[ Telecommunication management; Charging management; Diameter charging applications ]  [50].