A billing system is composed of a series of independent applications that, when run together, are referred to as the billing system. Its major components are as follows:

• CDR—This is used to record the details of the call. Usual information on a CDR includes start time of call, end time of call, duration of call, originating number, and terminating number. The CDR is stored until time of billing.

• guiding—This matches calls to customer calling plans. The application uses the start and end number and the duration and time of call to decide what the charge should be, based on the calling plans on the customer's record.

• rating application—This program applies the rate for the individual guided calls. Rating gives the call a value to be charged at the time of billing (not including any promotions, discounts, or taxes).

• billing—This is usually performed once a month. This job collects all of the rated calls that have been stored over the past 30 days. The program adds any promotions and discounts that are associated with the customer account. For example, if customers have called over a certain number of minutes, they might get a volume discount. In addition, taxes and credits are applied.

• invoicing—When the billing job is complete, a file is created that includes all of the customer's information. This file is sent to a print house to be converted to paper invoices. These invoices are then stuffed into envelopes, along with specific inserts targeted to the customer. Many companies will also create electronic statements and send customers their invoices via diskette, tape, or even e-mail; alternative billing practice is especially common for business customers.