This textbook is for a first course on computer networking. It can be used in both computer science and electrical engineering departments. In terms of programming languages, the book assumes only that the student has experience with C, C++, Java, or Python (and even then only in a few places). Although this book is more precise and analytical than many other introductory computer networking texts, it rarely uses any mathematical concepts that are not taught in high school. We have made a deliberate effort to avoid using any advanced calculus, probability, or stochastic process concepts (although we’ve included some homework problems for students with this advanced background). The book is therefore appropriate for undergraduate courses and for first-year graduate courses. It should also be useful to practitioners in the telecommunications industry.
What Is Unique About This Textbook?
The subject of computer networking is enormously complex, involving many concepts, protocols, and technologies that are woven together in an intricate manner. To cope with this scope and complexity, many textbooks are often organized around the “layers” of a network architecture. With a layered organization, students can see through the complexity of computer networking——they learn about the distinct concepts and protocols in one part of the architecture while seeing the big picture of how all parts fit together.
From a pedagogical perspective, our personal experience has been that such a layered approach indeed works well. Nevertheless, we have found that the traditional approach of teaching——bottom up; that is, from the physical layer towards the application layer——is not the best approach for a modern course on computer networking.
A Top-Down Approach
Our book broke new ground 16 years ago by treating networking in a top-down manner——that is, by beginning at the application layer and working its way down toward the physical layer. The feedback we received from teachers and students alike have confirmed that this top-down approach has many advantages and does indeed work well pedagogically.
Firstly, it places emphasis on the application layer (a “high growth area” in networking). Indeed, many of the recent revolutions in computer networking——including the Web, peer-to-peer file sharing, and media streaming——have taken place at the application layer. An early emphasis on application-layer issues differs from the approaches taken in most other texts, which have only a small amount of material on network applications, their requirements, application-layer paradigms (e.g., client-server and peer-to-peer), and application programming interfaces.
Secondly, our experience as instructors (and that of many instructors who have used this text) has been that teaching networking applications near the beginning of the course is a powerful motivational tool. Students are thrilled to learn about how networking applications work——applications such as e-mail and the Web, which most students use on a daily basis. Once a student understands the applications, the student can then understand the network services needed to support these applications. The student can then, in turn, examine the various ways in which such services might be provided and implemented in the lower layers. Covering applications early thus provides motivation for the remainder of the text.
Thirdly, a top-down approach enables instructors to introduce network application development at an early stage. Students not only see how popular applications and protocols work, but also learn how easy it is to create their own network applications and application-level protocols. With the top-down approach, students get early exposure to the notions of socket programming, service models, and protocols——important concepts that resurface in all subsequent layers. By providing socket programming examples in Python, we highlight the central ideas without confusing students with complex code. Undergraduates in electrical engineering and computer science should not have difficulty following the Python code.
An Internet Focus
Although we dropped the phrase “Featuring the Internet” from the title of this book, this doesn’t mean that we dropped our focus on the Internet. Indeed, nothing could be further from the case! Instead, since the Internet has become so pervasive, we felt that any networking textbook must have a significant focus on the Internet, and thus this phrase was somewhat unnecessary. We continue to use the Internet’s architecture and protocols as primary vehicles for studying fundamental computer networking concepts. Of course, we also include concepts and protocols from other network architectures. But the spotlight is clearly on the Internet, a fact reflected in our organizing the book around the Internet’s five-layer architecture: the application, transport, network, link, and physical layers.
Another benefit of spotlighting the Internet is that most computer science and electrical engineering students are eager to learn about the Internet and its protocols. They know that the Internet has been a revolutionary and disruptive technology and can see that it is profoundly changing our world. Given the enormous relevance of the Internet, students are naturally curious about what is “under the hood.” Thus, it is easy for an instructor to get students excited about basic principles when using the Internet as the guiding focus.
Teaching Networking Principles
Two of the unique features of the book——its top-down approach and its focus on the Internet——have appeared in the titles of our book. If we could have squeezed a third phrase into the subtitle, it would have contained the word “principles”.
The field of networking is now mature enough that a number of fundamentally important issues can be identified. For example, in the transport layer, the fundamental issues include reliable communication over an unreliable network layer, connection establishment/teardown and handshaking, congestion and flow control, and multiplexing. Three fundamentally important network-layer issues are determining “good” paths between two routers, interconnecting a large number of heterogeneous networks, and managing the complexity of a modern network. In the link layer, a fundamental problem is sharing a multiple access channel. In network security, techniques for providing confidentiality, authentication, and message integrity are all based on cryptographic fundamentals.
This textbook identifies fundamental networking issues and studies approaches towards addressing these issues. The student learning these principles will gain knowledge with a long “shelf life”——long after today’s network standards and protocols have become obsolete, the principles they embody will remain important and relevant. We believe that the combination of using the Internet to get the student’s foot in the door and then emphasizing fundamental issues and solution approaches will allow the student to quickly understand just about any networking technology.
Chapter Dependencies
The first chapter of this book presents a self-contained overview of computer networking. Introducing many key concepts and terminology, this chapter sets the stage for the rest of the book. All of the other chapters directly depend on this first chapter.
After completing Chapter 1, we recommend instructors cover Chapters 2 through 6 in sequence, following our top-down philosophy. Each of these five chapters leverages material from the preceding chapters.
After completing the first six chapters, the instructor has quite a bit of flexibility. There are no interdependencies among the last three chapters, so they can be taught in any order. However, each of the last three chapters depends on the material in the first six chapters. Many instructors first teach the first six chapters and then teach one of the last three chapters for “dessert.”
Jim Kurose & Keith Ross
2017