I want to develop a VoIP Billing System for only our company’s customer’s purpose, with MERA Softswitch.

I know the programming language PHP,ASP,Visual Basic,mySQL,MS SQL Server. But I don’t know anything about the RADIUS. I read from http://www.cisco.com/ but still I am in confused, from where I should start and what is requirement?

I will be very appreciated if any one can share me about my needs?

Thank you,