Section: 4.4.1.1 Rf
Content: The Rf reference point supports interaction between a CTF and a CDF. The following information may flow across this reference point in real-time: - Charging events for offline charging from the CTF to the CDF; - Acknowledgements for these events from the CDF to the CTF. The protocol(s) crossing this reference point shall support the following capabilities: - Real-time transactions; - Stateless mode ("event based charging") and statefull mode (“session based charging”) of operation; - Provide its own reliability mechanisms, e.g. retransmission of charging events, to run also on unreliable transport. In addition, the protocol should support changeover to a secondary destination (alternate CDF(s)) in case of the primary CDF not being reachable. This interface application is defined in TS 32.299[ Telecommunication management; Charging management; Diameter charging applications ]  [50]. The information contained in the charging events and the relevant chargeable events are specific to the domain / subsystem / service and are detailed in the respective middle tier TSs.