Offline Charging System (OFCS) - introduction to Gx interface

Last time I tried to familiarize You with Online Charging System (OCS), with was a introduction to Gy based on a diameter. But before I will go to the diameter, and all those CCRs and CCAs just I wanted to talk about Offline Charging System.

What is Offline Charging System (OFCS)?
According to TS 32.240 and TS 32.299 3GPP documentation:
Offline charging is a process where charging information for network resource usage is collected concurrently with that resource usage. The charging information is then passed through a chain of logical charging functions, which are described below. At the end of this process, CDR files are generated by the network, which are then transferred to the network operator's Billing Domain for the purpose of subscriber billing and/or inter-operator accounting (or additional functions, e.g. statistics, at the operator’s discretion). The BD typically comprises post-processing systems such as the operator's billing system or billing mediation device.

Generally offline charging is a mechanism where charging information does not affect, in real-time, the service rendered.
As it's always good to start with a high level design picture, let's start.

Fig. 1. Offline Charging high level architecture

Where:

CTF: Charging Trigger Function

CDF: Charging Data Function

CGF: Charging Gateway Function

BD: Billing Domain. This may also be a billing system/ billing mediation device.

Online Charging System (OCS) - introduction to Gy interface

Previously I wrote about network elements and interfaces between them, now it's time to write about most important thing in a mobile network, from operator's side.
How to charge customers for the fact they are using mobiles to many activities, including web surfing. Today I'm going to present some informations about Online Charging System (OCS), how does it work, its call flow basics scenarios, and last but not least basic principles.

As always is good to know about what we will be talking about, so please have a look at high level architecture concept of online charging.
Ro is reference point from the Charging Trigger Function (CTF) to the Charging Data Function (CDF) and the Online Charging Function (OCF) respectively, and are intended for the transport of charging events. Ro reference point is equivalent to Gy interface.

Fig. 1. Online charging high level architecture

Where:
CTF: Charging Trigger Function
CDF: Charging Data Function
CGF: Charging Gateway Function
BD: Billing Domain. This may also be a billing mediation device / post-processing system.