Today we will start with Online Charging, or Ro interface in our terminology. And because Online Charging is a bit more complex than Offline Billing, we’ll split it into several posts. In this first one we will take a look at so-call Direct-Debiting, which is used mainly for charging of SMS Service.
Perhaps from our Charging Overview you remember that we can use two different approaches to the Online Charging – Session based or Event based. SMS Ro Charging is using Event based mechanism. It is easier than the Session based and we will also need it later to complement the Session based Charging for the Voice service.
The SMS Charging architecture is standardized in 3GPP 32.274, the SMS online charging then uses the Credit-Control application as specified in TS 32.299.
The Online Charging is triggered over Ro Reference point. It is up to a Mobile Operator if they will signal charging operations from IP-SM-GW, SMSC, SMS Router or any combination of these. Typically the charging requests are sent from SMSC only. For simplicity we will refer only to the SMSC in the following text. SMSC may either directly support Ro interface, or it can use CAP (CAMEL) protocol which is then translated to Ro by an Interworking Function (IWF) as described in 3GPP 32.293.
The SMS charging may use two different models:
- Immediate Event Charging (IEC)
- Event Charging with Unit Reservation (ECUR)
In this post we will rather focus on IEC, as the ECUR is more complex and in my personal experience it is less common than IEC. The ECUR principle is specified in TS 32.299.