This book presents the architecture, fundamentals and analyzed the functional structure of Transmission Control Protocol (TCP). Besides, the book had focused on the congestion control mechanism used by typical TCP variants. It had reviewed the factors and the parameters that affect the behavior and the TCP performance, and had illustrated the design of the congestion control of six TCP source variants in addition to some other TCP's. Furthermore, in this book, a new TCP agent was generated with an enhanced congestion control algorithm which carry the general architecture of TCP Reno but it is based on new AIMD mechanism. This book had also discussed how to generate the agent of TCP in Network Simulator 2 (NS-2) and how to identify and configure the new TCP over NS-2 platform.