802.11ac: A Survival Guide

Preface

People keep moving. Networks still don’t, but they are being forced—sometimes quite painfully!—to accommodate the motion of users.

Wireless LANs are well established as The Way to Connect to the Network. When I first moved to Silicon Valley in the late 1990s, it was common to hear people talk about how they had run Ethernet through their homes so that every room had a network jack. Friends of mine worked with their home builders to install their own wiring, and occasionally a renovated home’s listing would breathlessly tout network connectivity. (To those who knew the technology, networking was always more than a patch panel installed someplace convenient.)

Today, network wiring no longer has a monopoly on that initial connection to the network edge. From Ethernet, the world has shifted to using wireless LANs, almost exclusively based on the 802.11 family of standards. In the space of a decade, Ethernet has been transformed from the underlying technology that made jokes like “will code for Internet access” possible into a mere support system for the wireless network that everybody attaches to.

The road to becoming the “first hop” technology in the network has required several steps. When 802.11 was first standardized in 1997, many of the networks ran at just one megabit, with a really fast network (for that point in time) running at double that speed. At that time, there was a huge debate between the proponents of frequency hopping technology and direct sequence technology. Direct sequence won out and led to the first mainstream technology, 802.11b. The wireless network community would move from a single radio carrier to multi-carrier technology with 802.11a and 802.11g, and on to multiple-input/multiple-output (MIMO) with 802.11n.

The next big milestone for 802.11 is a speed that is, as Dogbert would say, “big and round”^[1]—a gigabit per second of raw speed. That project is currently in development as 802.11ac. If you wished 802.11n were faster, buckle up and start reading!

Audience

This book is about 802.11ac, the draft standard “gigabit WiFi” specification. After the massive revision that was 802.11n, the technology changes in 802.11ac are (fortunately) not quite as large. To get the most out of this book, you’ll need to be familiar with the basics of the 802.11 Medium Access Control (MAC) layer, and have some familiarity with how pre-802.11ac networks were designed and built.

Note

Think of this book as the 802.11ac-specific companion to the earlier 802.11 Wireless Networks: The Definitive Guide from 2005, and 802.11n: A Survival Guide, published in 2012.

The intended reader is a network professional who needs to get in-depth information about the technical aspects of 802.11ac network operations, deployment, and monitoring. Readers in positions such as the following will benefit the most from this book:

• Network architects responsible for the design of the wireless networks at their places of business, whether the 802.11ac network is the first wireless LAN or an upgrade from a previous 802.11 standard

• Network administrators responsible for building or maintaining an 802.11ac network, especially those who want to make the transition from earlier 802.11a/b/g or 802.11n technologies

If you have picked up this book looking for information on security in 802.11ac, it’s in here. Fortunately, 802.11ac is just as secure as previous generations of 802.11. Security is part of the protocol, so if you are comfortable with 802.11 security in 802.11n or earlier, you know everything you need to know about 802.11ac.

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, email addresses, filenames, and file extensions.

Note

This icon signifies a tip, suggestion, or general note.

Caution

This icon indicates a warning or caution.

Safari® Books Online

Note

Safari Books Online (www.safaribooksonline.com) is an on-demand digital library that delivers expert content in both book and video form from the world’s leading authors in technology and business.

Technology professionals, software developers, web designers, and business and creative professionals use Safari Books Online as their primary resource for research, problem solving, learning, and certification training.

Safari Books Online offers a range of product mixes and pricing programs for organizations, government agencies, and individuals. Subscribers have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kaufmann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and dozens more. For more information about Safari Books Online, please visit us online.

How to Contact Us

Please address comments and questions concerning this book to the publisher:

O’Reilly Media, Inc.

1005 Gravenstein Highway North

Sebastopol, CA 95472

800-998-9938 (in the United States or Canada)

707-829-0515 (international or local)

707-829-0104 (fax)

We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at http://oreil.ly/80211ac_guide.

To comment or ask technical questions about this book, send email to [e-mail].

For more information about our books, courses, conferences, and news, see our website at http://www.oreilly.com.

Find us on Facebook: http://facebook.com/oreilly

Follow us on Twitter: http://twitter.com/oreillymedia

Watch us on YouTube: http://www.youtube.com/oreillymedia

Acknowledgments

This is my second book written with Meg Blanchette as editor. Meg kept the book moving along as best she could, which is no small feat given that I successfully pursued a pilot cetificate as I wrote this book. Meg regularly sought out opportunities for me to experiment as an author, most notably by encouraging me to participate in the early release program starting six months before the book’s final release. All the delays in publication are due entirely to my preoccupation with aviation, and would no doubt have been much worse without Meg’s diligent efforts to keep me on track.

I could not have asked for better readers to keep me motivated. As a direct result of all the notes and questions that I received, the book grew substantially during the review cycle. The review team included several 802.11 luminaries who are famous in their own right. My all-star review team consisted of (in alphabetical order, so I do not need to try and rank their many valuable and varied contributions in any sort of order):

Joe Fraher

Joe is a technical writer and colleague of mine at Aerohive, where he consistently produces documentation that is lucid, complete, and easy to use. Unlike me, he has mastered all the tools of his trade and handles the whole project from start to finish. One of Joe’s main contributions to the finished product you now hold is that he does not let me get away with glossing over anything. If you find that the book is consistent and complete, your thanks are properly given to Joe.

Changming Liu

Changming is the CTO at Aerohive, and a fountain of ideas both for Aerohive’s customers, and for me personally. I cannot name a conversation with him that I did not wish were longer.

Chris Lyttle

Chris heads up the wireless LAN practice at a major integrator, where he helps customers figure out how to use the technology that we build as an industry. Along the way, he chronicles the journey on his blog at Wi-Fi Kiwi, sharing valuable bits of information with anybody who is trying to run a wireless LAN.

Craig Mathias

At the Farpoint Group, Craig has been a prolific writer on 802.11 for many years. I am indebted to him for his many kind words over the years, and the encouragement he has always given me to continue writing on 802.11. Craig has asked me to be on many panels at industry events over the years, and has never failed to promote my books in his thoughtful introductions. As an analyst on the cutting edge, Craig is able to talk about new developments throughout the development process.

Matthew Norwood

Matthew, a senior technologist at an integrator, is one of the many people in the industry who has to do useful things with the crazy collection of technology parts we create. His networking mad science, which is about many components in addition to wireless LANs, unfolds at In Search of Tech.^[2] Matthew brought the sensibility of an expert network engineer to the book, and his review of the planning and integration parts of this book was particularly valuable.

Adrian Stephens

Adrian is one of the leaders of the 802.11 working group, where he has consistently used computers to save work instead of creating more of it. Talking to Adrian is like dropping questions into a deep well of technical knowledge. (For the record, I have yet to find the bottom.) I benefited from Adrian’s prodigious knowledge when we worked together on the 802.11-2012 revision, and he continues to serve the 802.11 community in ways too numerous to count. His comments on advanced MAC features and beamforming particularly strengthened the text, and his humourous^[3] comments added levity to the long slog of finishing the book, the effect of which was to help me see the light at the end of the tunnel.

Tim Zimmerman

Tim is an analyst with a technology advisory firm, and one of the most plugged-in people in the Wi-Fi industry. I am grateful for his time, and his many comments expanded multiple parts of the book in ways that will benefit you.

In addition to the formal review team, I benefited from the assistance of many other readers. Early release readers came from all across the world. Some of the most helpful were:

Jeff Haydel

Jeff is a talented field engineer for Aerohive, and was all that an author could ask for in an early release reader. He religiously read multiple drafts of the book, and was particularly helpful in striking the right balance between remaining faithful to the specification while trying to be concise and comprehensible.

Colleen Szymanik

Colleen Szymanik runs one of the largest and most complex wireless networks in the world, and her comments kept me focused on how to keep the book focused on information that would help working network administrators everywhere.

Ben Wilson

My colleague Ben Wilson has helped deploy more wireless networks than I care to count. His work takes him all across the UK, and I cannot figure out how he found time to review the book, let alone offer numerous useful suggestions.

One of the advantages of publishing the book early was that readers were able to interact with each other, both in person and on blogs. As I was working on incorporating technical review comments, I finally met Lee Badman face-to-face at Interop, and our brief discussion was critical to refining my thinking about the connectivity that will support future generations of 802.11ac access points.

I am grateful to readers who served as valuable sanity checks during the writing process, and helped keep me as focused as possible on the end goal. Terry Simons, who works on wireless LAN integration for Nest Labs, found the time to review the draft of this book and give me the detailed technical feedback of somebody who knows what it takes to make Wi-Fi just work. Tom Hollingsworth offered encouragement at a critical juncture. Michele Chubirka, the security podcaster for Packet Pushers, provided a much-welcomed reality check during the middle of the long twilight of the book. Kelly Davis-Felner and Bill Solominsky at the Wi-Fi Alliance offered encouragement both in person at the Wi-Fi Alliance meeting where much of this book was written, and by drafting me into writing for the Wi-Fi Alliance on 802.11ac.

---

^[1] As always, Dogbert was ahead of the curve. He was frightening people way back in 1994.

^[2] Matthew also wrote the nicest thing I’ve ever read about my writing on his own blog at http://www.insearchoftech.com/2013/04/11/the-curse-of-matthews-books/.

^[3] Adrian is English, so I deviate from the American spelling just to show him that I can be bilingual.