Foreword to the Sixth Edition

​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.

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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