Authentication is the process of determining who the user is.
It can take the form of assuring that data has come from its claimed source, or of corroborating the claimed identity of a communicating party. Authorization is the process of enforcing policies - of determining what types or qualities of activities, resources, or services a user is permitted. Accounting is the tracking of which services are used, by whom, when, and for how long. Accounting is carried out by logging of session statistics and usage information and is used for authorization control, billing, trend analysis, resource utilization, and capacity planning activities. A AAA Server is a software application that performs these AAA functions, usually by interacting with network access or gateway devices and databases and directories containing user information.