How does the Remote Authentication Dial-In User Service (RADIUS) function?

What will be an ideal response?

ANSWER: RADIUS is an open-source standard developed by Livingston Enterprises in 1991 and later standardized by the IETF. It runs in the Application layer and can use either UDP or, as of 2012, TCP in the Transport layer. RADIUS treats authentication and authorization as a single process, meaning that the same type of packet is used for both functions, while accounting is a separate process. RADIUS can operate as a software application on a remote access server or on a computer dedicated to this type of authentication, called a RADIUS server. Because RADIUS servers are highly scalable, many ISPs use a RADIUS server as a central authentication point for wireless, mobile, and remote users. RADIUS services are often combined with other network services on a single machine.