Radius is a protocol for carrying information related to authentication, authorization, and configuration between a Network Access Server (NAS) that desires to authenticate its links and a shared Authentication Server.
This tutorial starts off with an overview of Radius followed by its features, operations, packet format, and attributes. Subsequently, the tutorial provides a few examples of Radius request and response, and terminates with a brief introduction to Diameter, a planned replacement of Radius.
This is an introductory tutorial designed for beginners to help them understand the basics of Radius.
There are no prerequisites as such, however it would help if you have a basic understanding of client/server environment.