TCP/IP Analysis and Troubleshooting Toolkit

CHAPTER 6

Transmission Control Protocol

As you move up higher and higher into each layer of the OSI model, protocols become more complex. TCP is no exception to this statement. Its complexity derives from TCP's rich set of features and functionality. By not learning its inner functions, you risk missing the ability to completely understand the protocol, which, in troubleshooting scenarios, can be deadly. This chapter seeks to help you understand TCP from the inside out.

Introduction to TCP

Chapter 6 is broken down into four main sections.

• First is the one you are reading, the introduction. In it I discuss TCP at the 10,000-foot level, briefly glancing over its many intricacies. TCP is a difficult protocol to explain without getting into its many intricate details. I have purposely left out many of these details in the first section. I simply want you to be familiar with their existence before we talk about their use. Thus, I immediately describe the TCP Header, which will be the basis for our discussion on the rest of the protocol's functionality. I also talk about what a reliable transport protocol does and what it needs to be able to do its job. Again, these subjects will be at a very broad level so that the reader may glean a look at what is to come later in the chapter.
• Second, I talk about the connection-oriented nature of TCP, how it opens, closes, and handles connection problems between hosts.
• Third, I talk in depth about how TCP handles flow control between two hosts and ...