This book presents an Internet Service Provider Billing System with unique characteristics and rich feature content, enabling significant cost reduction. The main mechanism of this system is controlling the Online Charging System (OCS). The support for high user load capacity, traffic management, and revenue management makes this system ideal for any small/medium/large ISP. The features of this System are: Tracking, Re-invoicing, Adjustments/credits account creation, verifying and controlling the access time for both LAN and WAN systems in a real time environment. The system includes unlimited scalability, Industry-leading billing capabilities, Webbased administration. It was tested and ran successfully on an Intranet system, that contains a Windows Domain Controller and each PC was a member of that Domain Controller.