This chapter covers
- How the Transmission Control Protocol and User Datagram Protocol provide Layer 4 addressing and session multiplexing
- How TCP provides features like reliable communication and flow control
- Comparing TCP and UDP, and the situations in which each is preferred
In chapter 3 of this book, we covered physical cables, connectors, and ports—Layer 1 of the TCP/IP model. In other chapters, we covered the Data Link Layer (Layer 2): MAC addresses, frame switching, VLANs, STP, and other related topics. We have also spent many pages on the Network Layer (Layer 3): IPv4 and IPv6 addressing, subnetting, packet forwarding, static and dynamic routing, first-hop redundancy protocols, etc. In this chapter, we will venture beyond those first three layers and take a look at Layer 4 of the TCP/IP model: the Transport Layer. Specifically, we will examine the two major Layer 4 protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), which are exam topic 1.5: Compare TCP to UDP.
22.1 The role of Layer 4
In chapter 4 of this book, we took a high-level look at the role of each layer of the TCP/IP model. For review, figure 22.1 summarizes the role of each layer.