Revision with unchanged content. How to understand the fundamental nature of wired and wireless networks is a critical and interesting issue. With the rapid development of networks, the performance is obtaining more and more attention. This book is trying to answer the following questions. (i) what are the stability characteristics of TCP flows over a wired networks, which is in the linear scale, including the definition of stability, the normalized fluid model, general AIMD parameter pairs, etc; (ii) what are the performance of TCP flows under an aggressive scale, including the stochastic model, homogeneous round trip time, heterogeneous round trip time, mixture of long live and short live flows, etc; (iii) when TCP is applied to wireless networks, how to characterise the TCP influence? How to set up a two-level model? What is the packet level performance and what is the call level performance. This book is useful to the professionals in network community like professors, graduate students, and researchers.