1.11 Summary

In this chapter we've covered a tremendous amount of material! We've looked at the various pieces of hardware and software that make up the Internet in particular, and computer networks in general. We started at the "edge" of the network, looking at end systems and applications, and at the transport service provided to the applications running on the end systems. Using network-based distributed applications as examples, we introduced the notion of a protocol - a key concept in networking. We then dove deeper inside the network, into the network core, identifying packet-switching and circuit switching as the two basic approaches for transporting data through a telecommunication network, and examining the strengths and weaknesses of each approach. We then looked at the lowest (from an architectural standpoint) parts of the network -- the link layer technologies and physical media typically found in the access network.

In the second part of this introductory chapter we then took the broader view on networking. From a performance standpoint, we identified the causes of packet delay and packet loss in the Internet. We identified key architectural principles (layering, service models) in networking. We then examined the structure of today's Internet. We finished our introduction to networking with a brief history of computer networking. The first chapter in itself constitutes a mini-course in computer networking.

So, we have indeed covered a tremendous amount of ground in this first chapter! If you're a bit overwhelmed, don't worry. In the following chapters we will revisit all of these ideas, covering them in much more detail (that's a promise, not a threat!). At this point, we hope you leave this chapter with a still-developing intuition for the pieces that make up a network, a still-developing command for the vocabulary of networking (don't be shy to refer back to this chapter), and an ever-growing desire to learn more about networking. That's the task ahead of us for the rest of this book.

Roadmapping This Book

Before starting any trip, we should always glance at a roadmap in order to become familiar with the major roads and junctures that lie between us and our ultimate destination. For the trip we are about to embark on, the ultimate destination is a deep understanding of the how, what and why of computer networks. Our roadmap is the sequence of chapters of this book:

Computer Networks and the Internet
Application Layer
Transport Layer
Network Layer and Routing
Link Layer and Local Area Networks
Multimedia Networking
Security in Computer Networks
Network Management

Taking a look at this roadmap, we identify Chapters 2 through 5 as the four core chapters of this book. You should notice that there is one chapter for each of the top four layers of the Internet protocol stack. Further note that our journey will begin at the top of the Internet protocol stack, namely, the application layer, and will work its way downward. The rationale behind this top-down journey is that once we understand the applications, we can then understand the network services needed to support these applications. We can then, in turn, examine the various ways in which such services might be implemented by a network architecture. Covering applications early thus provides motivation for the remainder of the text.

The second half of the book -- Chapters 6 through 8 -- zoom in on three enormously important (and somewhat independent) topics in modern computer networking. In Chapter 6 (Multimedia Networking), we examine audio and video applications -- such as Internet phone, video conferencing, and streaming of stored media. We also look at how a packet-switched network can be designed to provide consistent quality of service to audio and video applications. In Chapter 7 (Security in Computer Networks), we first look at the underpinnings of encryption and network security, and then examine how the basic theory is being applied in broad range of Internet contexts, including electronic mail and Internet commerce. The last chapter (Network Management) examines the key issues in network management as well as the Internet protocols that address these issues.

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