TACACS (Terminal Access Controller Access Control System) is a protocol within the AAA framework. It was originally developed to provide centralized authentication, authorization, and accounting for remote network access, typically used with terminal servers.

There are two versions of TACACS: TACACS and TACACS+:

TACACS: This is an older version of the protocol and stands for Terminal Access Controller Access Control System. It primarily provides authentication services, and it separates the authentication, authorization, and accounting functions into three separate transactions. It doesn't support encryption for data transmission.

TACACS+: This is an extended and improved version of TACACS, and the "+" sign indicates its enhanced capabilities. TACACS+ is more comprehensive, supporting all three aspects of AAA (Authentication, Authorization, and Accounting) within a single packet exchange. It offers improved security through encryption, making it more suitable for modern network security requirements. TACACS+ is often used in environments where strong security and detailed control over network access are essential.

In summary, TACACS protocol (specifically TACACS+) is used as part of the AAA framework to manage network access by providing authentication, authorization, and accounting services. It helps ensure secure and controlled access to network resources while maintaining a record of user activities.