The final "A" in "AAA" is for Accounting. Even though a majority of engineers believe the terms accounting and billing have the same meaning, accounting involves more than tracking a user's total number of phone call minutes or data packets. A variety of applications are defined for accounting:
Auditing: The act of verifying the correctness of an invoice submitted by a service provider, or the conformance to usage policy, security guidelines, and so on.
Cost allocation: With the convergence of telephony and data communications, there is increasing interest in understanding the cost structure associated to each of the telephony and data portions.
Trend analysis: Typically used in forecasting future usage for the purpose of capacity planning.
Each of the applications above may be processed at a different logic management entity. But in general, accounting is concerned with collection of information on resource consumption at all or specific parts of the network. This information is generally referred to as accounting data or accounting metrics. Typically, the network device providing services to a user collects information about user's resource consumption according to the accounting application's needs.
The accounting data collected by the network device is then carried by the accounting protocols over to the management entities responsible for each accounting application. As will be explained later on, each of these different accounting applications may have varying ...