Prepaid Billing systems, (which can also be called charging systems in day-to-day talks), run the billing process for the prepaid customer accounts.
They heavily use the online charging mechanism rather than offline charging that we typically see in the postpaid billing systems. Online charging systems rate the usage on-the-fly and charge the user account immediately.
Prepaid billing environment is composed of several different systems. And the most important one is the charging system. Prepaid Charging systems are integrated with the switches (MSC, PSTN), SMSC, MMSC, GGSN, Interconnect and other VAS applications. Those service infrastructure equipments are configured to ask an authorization from the charging manager before proceeding to give a service.
Charging systems communicate with (or employs) several other systems to charge the customer usage. One of them is the rating system which calculates the cost of the usage. Rating systems maintain the tariffs, discounts and campaign related information.
Charging systems ask rating systems the cost (in terms of dollars, credits etc) of the usage (volume, time or event based) and then try to apply it to the customer account balance. They do this by communicating with a balance manager. Balance manager systems manage the customer account balance.
There are 2 mechanisms that charging managers use in order to debit from the account balance:
First mechanism is the “direct debit” mechanism. In this approach, balance manager directly debits a pre-defined amount. For example, a debit is applied each 30 seconds (For those 30 seconds.) If you terminate the session at 25th second, the remaining 5 seconds are rated and refunded back to the account.
The second mechanism is the “unit reservation” mechanism. Here, rather directly debiting from the account, you reserve some of the balance. When the call is complete (or SMS, MMS has reached it destination) the reserved amount is committed.
Voucher management is also an important function that needs to be mentioned about. Voucher managers manage the lifecycle of the voucher that are used to credit the customer account balances. Therefore, voucher managers have a direct interface with the balance managers. (and possibly with other systems such as CRM, Fraud managers etc.)
Charging platforms also employ IVR functionalities. These are usefull to inform the user about the current balance, crediting the balance and notifying the user before any call drop due to insufficient balance.
(If the charging system cannot do the charging, due to some reasons, it outputs a CDR file including the session details. This CDR is post processed and applied to the account balance.)
Charging manager, balance manager, rating manager, voucher management and IVR can be sold separately or combined in a single “prepaid billing” platform.
Operators around the world started consolidating their prepaid and postpaid billing platforms. This is called convergent billing. This approach reduces the complexities, license/hardware costs and operational expenses. I’ll try to comment on convergent billing in another post.