VoLTE Offline Charging – Voice Call

In the last post we talked about VoLTE charging on a high level. This time we will zero-in and focus on a role of Telephony Application Server (TAS) in offline charging during a Voice/Video Call. Charging on the TAS is described in the 3GPP 32.260 and 32.275. The basic charging is fairly simple, but we also have to count with Supplementary Services, Roaming Scenarios and rainy-days scenarios.

TAS Charging, Ro, Rf

We already know that the 3GPP specification requires Network Elements like TAS to provide offline billing so that service providers can collect and correlate charging information from a variety of sources as well as to generate CDRs. An IMS system is composed of many entities that can generate charging events which need to be collated in order to generate a bill for the customer. These elements are referred in our terminology as the Charging Trigger Functions (CTF). The CTF function works in connection with TAS call processing by receiving SIP call events, translating SIP messages into Diameter messages with call parameters copied into 3GPP-defined AVP set, and sending Accounting Request (ACR) messages to the external CDF. The CDF acknowledges the receipt of ACR message by sending back an Accounting Answer (ACA) message indicating success or failure of the operation. The communication between CTF (TAS) and CDF happens over the Rf interface, which uses the Base Diameter protocol. 

It’s All about Money! VoLTE Charging

Charging has been for a long time on my todo list. Now it’s the time and you can expect couple of posts related to charging, mainly Online Charging. Today we’ll go through the most basic stuff. For details refer to 3GPP 32.240.

Charging is a world of its own, it has its own rules, flows and well, also documentation. To really understand how to properly charge your calls, data, or messages is probably the same or even bigger challenge than to understand the actual service.

Charging Specification – source 3GPP 32.240

Charging Mechanisms

GSM/UMTS/EPC networks provide functions that implement offline and/or online charging mechanisms on the bearer (e.g. EPC), subsystem (e.g. IMS) and service (e.g. SMS) levels. In order to support these charging mechanisms, the network performs real-time monitoring of resource usage for those three levels in order to detect the relevant chargeable events.

In general we recognize Online and Offline charging mechanisms. They may be performed simultaneously and independently for the same charging events.