Having recently received the foreword for the sixth edition of Computer Networks: A Systems Approach from David Clark, we thought it would be fun to pull out his original foreword from 1996, which will also be republished in the forthcoming book. 

"Plus ça change, plus c'est la même chose​."

Foreword to the First Edition

The term *spaghetti code* is universally understood as an insult. All good computer scientists worship the god of modularity, since modularity brings many benefits, including the all-powerful benefit of not having to understand all parts of a problem at the same time in order to solve it. Modularity thus plays a role in presenting ideas in a book, as well as in writing code. If a book’s material is organized effectively—Modularly—the reader can start at the beginning and actually make it to the end.

The field of network protocols is perhaps unique in that the “proper” modularity has been handed down to us in the form of an international standard: the seven-layer reference model of network protocols from the ISO. This model, which reflects a layered approach to modularity, is almost universally used as a starting point for discussions of protocol organization, whether the design in question conforms to the model or deviates from it.

It seems obvious to organize a networking book around this layered model. However, there is a peril to doing so, because the OSI model is not really successful at organizing the core concepts of networking. Such basic requirements as reliability, flow control, or security can be addressed at most, if not all, of the OSI layers. This fact has led to great confusion in trying to understand the reference model. At times it even requires a suspension of disbelief. Indeed, a book organized strictly according to a layered model has some of the attributes of spaghetti code.

Which brings us to this book. Peterson and Davie follow the traditional layered model, but they do not pretend that this model actually helps in the understanding of the big issues in networking. Instead, the authors organize discussion of fundamental concepts in a way that is independent of layering. Thus, after reading the book, readers will understand flow control, congestion control, reliability enhancement, data representation, and synchronization, and will separately understand the implications of addressing these issues in one or another of the traditional layers.

This is a timely book. It looks at the important protocols in use today—especially the Internet protocols. Peterson and Davie have a long involvement in and much experience with the Internet. Thus their book reflects not just the theoretical issues in protocol design, but the real factors that matter in practice. The book looks at some of the protocols that are just emerging now, so the reader can be assured of an up-to-date perspective. But most importantly, the discussion of basic issues is presented in a way that derives from the fundamental nature of the problem, not the constraints of the layered reference model or the details of today’s protocols. In this regard, what this book presents is both timely and timeless. The combination of real-world relevance, current examples, and careful explanation of fundamentals makes this book unique.

​David Clark of MIT has written the foreword for every edition of "Computer Networks: A Systems Approach" since its inception. Here is his foreword to the soon-to-be-released sixth edition.

Readers: before you start the book, first take a moment and set your time machine to 1996. That is when the first edition of this book was published. Do you remember 1996? Were you alive then?  People forget how long ago the foundations of the Internet were laid.

In 1996, the NSFNET had just been decommissioned, and the commercial phase of the Internet was just beginning. The first search engine (Alta Vista—do you remember?) had just been demonstrated. Content delivery networks did not exist-- Akamai was founded two years later in 1998, the same year Google was officially born. Cloud was only a distant haze on the horizon. And there was no such thing as residential broadband or consumer wireless.  We used dialup modems—the 56K modem had just been invented. There were packet radios before then, but they were slower than dialup and the size of a beer fridge. You needed a truck or at least a Jeep to be mobile.

And in 1995 or so, Larry and Bruce decided to write this book. It may be hard, from today’s perspective, to remember how important a book like this was in 1996. It captured a lot of tacit knowledge and made it available to anyone who would read. And rather than just reciting a series of protocol descriptions, it taught how the parts fit together. It taught how the Internet worked, not just what the parts were.

One way to think about how the Internet has evolved is through the lens of the application designer. After all, the purpose of the Internet as a packet transport system is to support apps. Only geeks and performance freaks send packets for the fun of it.  In 1996, if you wanted to build an application, the ecosystem included the IP packet transport service, TCP to smooth out the losses at the Internet layer, the DNS, and that was about it. Anything else the application designer needed had to be built from scratch.

Now an application designer has lots of resources to build on: cloud and cloud networks, other global networks that can hook services together, CDNs, app development environments and so on. Some of these may seem quite different from what we had in 1996 and in detail they are. Consider cloud. (I hate the choice of the term—to me “cloud” suggests something soft and fluffy, but if you have ever seen a data center the size of a football field that sucks megawatts, you would not think soft and fluffy. But never mind…) Data centers have become very sophisticated about cost, energy efficiency, performance and resilience. There is a lot to learn about how to build a modern data center. But the fundamentals are the same: packet forwarding, statistical capacity sharing, transport protocols, routing protocols, the pursuit of generality and broad utility, and the like.

Looking forward, technologies such as cloud are clearly central and this edition devotes considerable attention to cloud. Requirements such as improving security are critical, and the book discusses additional issues related to security: trust, identity, and the latest hot topic—blockchain.  However, if you were to look at the first edition, many of the foundational concepts are the same. But this edition is the modern version of the story, with up to date examples and modern technology. Enjoy.


David Clark
MIT
October 2020