Preface
=======

It has been nearly ten years since the 5th Edition of *Computer
Networks: A Systems Approach* was published. Much has changed in that
time, most notably, the explosion of the cloud and smartphone apps onto
the scene. In many ways, this is reminiscent of the dramatic affect the
Web was having on the Internet when we published the 1st Edition of the
book in 1996.

The 6th Edition adapts to the times, but keeps the *Systems Approach* as
its north star. In broad strokes, we updated this new edition in three
main ways:

-  We refreshed the examples to reflect the current state of the world.
   This includes deleting anachronisms (e.g., dial-up modem), using
   popular applications (e.g., Netflix, Spotify) to motivate the
   problems being addressed, and updating the numbers to represent the
   state-of-the-art technology (e.g., 10-Gbps Ethernet).

- We connect the dots between the original research that led to the
   development of technologies like multicast, real-time video
   streaming, and quality-of-service, and the now-familar cloud
   applications like GoToMeeting, Netflix, and Spotify. This is in
   keeping with our emphasis on the design process and not just the
   end result, which is especially important today since so much the
   Internet is primarily available in proprietary commercial services.

- We place the Internet in the broader context of the Cloud, and just
   as importantly, in the context of the commerial forces that are
   shaping the Cloud. This has minimal impact on the technical details
   presented throughout the book, but it is discussed in a new
   *Perspective* section at the end of each chapter. We hope one
   side-effect of this discussion is to foster an appreciation for the
   Internet’s continuous evolution, and the opportunity for innovation
   this represents.

More specifically, the 6th Edition includes the following major changes:

-  New Perspective Section in Chapter 1 introduces the recurring *Cloudification* theme.
-  New Section 2.8 describes the *Access Network*, including Passive
   Optical Networks (PON) and 5G’s Radio Access Networks (RAN).
-  Section 3.4 updated to include descriptions of *White-Box Switches*
   and *Software-Defined Networks* (SDN).
-  New Perspective Section in Chapter 3 describes *VXLANs* and the
   role of overlays in the Cloud.
-  New Perspective Section in Chapter 4 describes how the *Cloud*
   impacts the Internet’s structure.
-  Section 5.3 expanded to include a description of *gRPC*.
-  Sections 6.3 and 6.4 updated to include descriptions of *TCP CUBIC,
   DCTCP,* and *BBR*.
-  Section 6.4 expanded to include a description of *Active Queue
   Management* (AQM).
-  Section 7.1 expanded to include a desciption of *Protocol Buffers*.
-  Section 7.2 expanded to include a desciption of *HTTP Adaptive
   Streaming*.
-  New Section 8.1 introduces the duality of *Threats* and *Trust*.
-  New Perspective Section in Chapter 8 describes *Decentralized
   Identity Management* and the role of *Blockchains*.
-  Section 9.1 updated to include a description of *HTTP/2*, along with
   a discussion of *REST*, *gRPC*, and *Cloud Services*.
-  Section 9.3 expaned to include a description of modern *Network
   Management Systems* including the use of *OpenConfig* and *gNMI*.

We would like to acknowledge the following people for their help with
new content:

-  Larry Brakmo: TCP Congestion Control
-  Carmelo Cascone: White-Box Switches
-  Charles Chan: White-Box Switches
-  Jude Nelson: Decentralized Identity
-  Oguz Sunay: Cellular Networks
-  Thomas Vachuska: Network Management

And the following individuals (github users) for their various
contributions:

-  Mohammed Al-Ameen
-  Andy Bavier
-  Manuel Berfelde
-  Chris Goldsworthy
-  John Hartman
-  Diego López León
-  Matteo Scandolo
-  Mike Wawrzoniak
-  罗泽轩 (spacewander)
-  Arnaud (arvdrpoo)
-  Desmond (kingdido999)
-  Guo (ZJUGuoShuai)
-  Hellman (eshellman)
-  Xtao (vertextao)

| Larry & Bruce
| August 2019