RADIUS as developed with the idea of allowing its users or clients to be able to authenticate to a dial-in access server. So basically it is a client server protocol and he client here is the firebox and the server is the RADIUS server.
The authentication mechanism start by user who sends a message to the RADIUS server. Then the RADIUS server upon receiving the message accept or denies it. It accepts if the client is configured to the server.
A large amount of additional information can be sent by the RADIUS server in its Access-Accept messages with users so we can say that RADIUS is uitable for what are called "high-volume service control applications" such as dial-in access to a corporate network.
Programming languages have functions because, they are the set of operations that may be applied to objects of that particular class. for an example I will attach a function, you just check it
