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Telecommunication companies need an effective and accurate billing system to be able to assure their revenue. Billing systems process the usage of network equipment that is used during the service usage into a single Call Detail Record (CDR). The billing process involves receiving billing records from various networks, determining the billing rates associated with the billing records, calculating the cost for each billing record, aggregating these records periodically to generate invoices, sending invoices to the customer, and collecting payments received from the customer.

Billing system is very complex starting from network elements that generate usage to the billing system to usage collection, mediation, rating, and invoicing. To simplify the process I will introduce a simple system usage scenario as shown in the following figure. The system user navigates through the company site and views company services, and he decides to order one of the available services. If he has no account, he signs up for a new account, else he signs in. Then the user asks to conduct an order with the selected service. The service may be prepaid where he has to pay to have credits to use the service, or it may be postpaid, where he has to pay if the service has installation or setup fees, and later on he will pay for his usage of each billing cycle.