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In computer security, AAA commonly stands for authentication, authorization and accounting. It refers to a security architecture for distributed systems, which enables control over which users are allowed access to which services, and how much of the resources they have used. Two network protocols providing this functionality are particularly popular: the RADIUS protocol, and its newer Diameter counterpart.
Authentication refers to the process where an entity's identity is authenticated, typically by providing evidence that it holds a specific digital identity such as an identifier and the corresponding credentials. Examples of types of credentials are passwords, one-time tokens, digital certificates, digital signatures and phone numbers (calling/called).
The authorization function determines whether a particular entity is authorized to perform a given activity, typically inherited from authentication when logging on to an application or service. Authorization may be determined based on a range of restrictions, for example time-of-day restrictions, or physical location restrictions, or restrictions against multiple access by the same entity or user. Typical authorization in everyday computer life is for example granting read access to a specific file for authenticated user. Examples of types of service include, but are not limited to: ip address filtering, address assignment, route assignment, quality of Service/differential services, bandwidth control/traffic management, compulsory tunneling to a specific endpoint, and encryption.
Accounting refers to the tracking of network resource consumption by users for the purpose of capacity and trend analysis, cost allocation, billing. In addition, it may record events such as authentication and authorization failures, and include auditing functionality, which permits verifying the correctness of procedures carried out based on accounting data. Real-time accounting refers to accounting information that is delivered concurrently with the consumption of the resources. Batch accounting refers to accounting information that is saved until it is delivered at a later time. Typical information that is gathered in accounting is the identity of the user or other entity, the nature of the service delivered, when the service began, and when it ended, and if there is a status to report.
Usage of AAA servers in CDMA data networks 
AAA servers in CDMA data networks are entities that provide Internet Protocol (IP) functionality to support the functions of authentication, authorization and accounting. The AAA server in the CDMA wireless data network architecture is similar to the HLR in the CDMA wireless voice network architecture.
Types of AAA servers include the following:
- Access Network AAA (AN-AAA) – Communicates with the RNC in the Access Network (AN) to enable authentication and authorization functions to be performed at the AN. The interface between AN and AN-AAA is known as the A12 interface.
- Broker AAA (B-AAA) – Acts as an intermediary to proxy AAA traffic between roaming partner networks (i.e., between the H-AAA server in the home network and V-AAA server in the serving network). B-AAA servers are used in CRX networks to enable CRX providers to offer billing settlement functions.
- Home AAA (H-AAA) – The AAA server in the roamer's home network. The H-AAA is similar to the HLR in voice. The H-AAA stores user profile information, responds to authentication requests, and collects accounting information.
- Visited AAA (V-AAA) – The AAA server in the visited network from which a roamer is receiving service. The V-AAA in the serving network communicates with the H-AAA in a roamer's home network. Authentication requests and accounting information are forwarded by the V-AAA to the H-AAA, either directly or through a B-AAA.
Current AAA servers communicate using the RADIUS protocol. As such, TIA specifications refer to AAA servers as RADIUS servers. However, future AAA servers are expected to use a successor protocol to RADIUS known as Diameter.
The behavior of AAA servers (radius servers) in the CDMA2000 wireless IP network is specified in TIA-835.
- C. Rigney, S. Willens, A. Rubens, W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", IETF RFC 2865, June 2000.
- P. Calhoun, J. Loughney, E. Guttman, G. Zorn, J. Arkko, "Diameter Base Protocol", IETF RFC 3588, September 2003.
- Sasu Tarkoma, "Mobile Middleware: Architecture, Patterns and Practice", John Wiley and Sons, 2009, pp. 248–251. ISBN 987-0-470-74073-6.
- Bernard Aboba, Jari Arkko, David Harrington, "Introduction to Accounting Management", RFC 2975, IETF, Oct. 2000.