Part 2 book “Data communications and networking” has contents: Introduction to network layer, network-layer protocols, unicast routing, multicast routing, next generation IP, introduction to transport layer, network management, introduction to application layer, and other contents. | PA R T V Transport Layer In the fifth part of the book, we discuss the transport layer. Although this part is made of only two chapters, the chapters are long. Chapter 23 discusses the general idea and issues behind the transport layer. Chapter 24 discusses the three current protocols in the Internet: UDP, TCP, and SCTP. Chapter 23 Introduction to Transport Layer Chapter 24 Transport-Layer Protocols 689 CHAPTER 23 Introduction to Transport Layer T he transport layer in the TCP/IP suite is located between the application layer and the network layer. It provides services to the application layer and receives services from the network layer. The transport layer acts as a liaison between a client program and a server program, a process-to-process connection. The transport layer is the heart of the TCP/IP protocol suite; it is the end-to-end logical vehicle for transferring data from one point to another in the Internet. This chapter is the first chapter devoted to the transport layer; we discuss the Internet transport-layer protocols in the next chapter. We have divided this chapter into two sections: ❑ The first section introduces the idea behind a transport-layer protocol. We first discuss the general services we normally require from the transport layer, such as process-to-process communication, addressing, multiplexing and demultiplexing, error, flow, and congestion control. We then show that the transport-layer protocols are divided into two categories: connectionless and connection-oriented. We discuss the characteristics of each category and show the application of each category. ❑ The second section discusses general transport-layer protocols. These protocols concentrate on flow and error control services provided by an actual transportlayer protocol. Understanding these protocols helps us better understand the design of the transport-layer protocols in the Internet, such as UDP, TCP, and SCTP. In this section, we first describe an imaginary .
