1 TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL OVERVIEW

This first chapter provides an overview of Transmission Control Protocol (TCP)/Internet Protocol (IP), which is an Internet protocol stack to perform com-munications between two computers, or hosts, through the Internet. It is a collection of different protocols. A protocol is a set of rules that controls the way data is trans-mitted between hosts. 1.1 FUNDAMENTAL ARCHITECTURE Figure 1.1 shows the Open Systems Interconnection (OSI) reference model and the Internet protocol stack. The International Standardization Organization (ISO) speci-fies a guideline called the OSI reference model. It is an abstract description for layered communications and computer network protocol design. It consists of seven layers, which are, from the bottom, physical, data link, network, transport, session, presen-tation, and application, as shown in Figure 1.1a. The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. At the physical layer, data is recognized, or handled, as bits. At the data link layer, data is handled as frames. At the network layer, data is recognized as packets. In the transport layer, data is handled as segments or datagrams. In the remaining upper layers, users ’ information is recognized