802.11n: A Survival Guide

Preface

People still move. Networks still don’t.

A decade ago, I first wrote that people moved, and networks needed to adapt to the reality that people worked on the go. Of course, in those days, wireless LANs came with a trade-off. Yes, you could use them while moving, but you had to trade a great deal of throughput to get the mobility. Although it was possible to get bits anywhere, even while in motion, those bits came slower. As one of the network engineers I worked with put it, “We’ve installed switched gigabit Ethernet everywhere on campus, so I don’t understand why you’d want to go back to what is a 25-megabit hub.” He underestimated the allure of working on the go.

In the rubble of the early 2000s Internet bust, wireless LANs were one of the first new technologies to cut through the gloom. As they gained in popularity, they morphed from an expensive toy to show off and became a must-have technology. My apartment had a wireless LAN very early, and I remember when I showed it off with pride. In the days of 2 Mbps 802.11 networks (or, if you were rich, an 11 Mbps 802.11b network!), all you had to do was beat the speed of your Internet link, which was not particularly hard.

What made 802.11n the next big step in the wireless revolution is that it was the first time that a wireless LAN delivered reasonable performance. Wireless LANs first took root in industries with highly mobile employees: hospital medicine, logistics, and education. Trading speed for mobility is a good exchange when you are on the move. It looks less attractive when you are relatively stable. 802.11n was the technology that buried the trade-off of speed for mobility. For the first time, it was possible to build a wireless network without compromise.

To build your network without wires, you don’t have a choice: you’re about to get familiar with 802.11n.

Audience

This book is about 802.11n, which was itself a major revision to the previous specification. To get the most out of it, you’ll need to be familiar with the basics of the 802.11 MAC and how it orchestrates access to the medium. It will help to be somewhat familiar with how 802.11 networks were designed before 802.11n came along. In a sense, this book is the 802.11n-specific companion to the earlier 802.11 Wireless Networks: The Definitive Guide (2nd edition), which was last revised in 2005.

The intended reader is a network professional who needs to delve into the technical aspects of 802.11n network operations, deployment, and monitoring, such as:

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

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

One class of people for which I’ve specifically not written is the security officer. Ten years ago, “802.11” and “security” were not usually used together in the same sentence, unless it was derisive. Of the many changes that have occurred in the world of 802.11 since I last put virtual pen to virtual paper, none pleases me more than the acceptance of 802.11 as a readily secured network access layer. As an industry, we fought the battle to secure wireless LANs, and we won. My position as chair of the Wi-Fi Alliance’s security efforts is generally boring—and I hope it stays that way!

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Acknowledgments

It has been just long enough since I last wrote a book for me to forget the long slog that is writing. Although some writers will tell you that there is a tyranny in staring at a blank page, I have found that the hardest part is turning a completed rough draft into an actual book. As always, I benefited from a tremendous supporting cast at O’Reilly, starting with Mike Loukides, who got the project off the ground, and Meghan Blanchette, who took on the much harder task of making me finish.

I could not have asked for a better review team, which includes several 802.11 luminaries who are famous in their own right. My all-star review team consisted of (in alphabetical order):

David Coleman

A well-known wireless LAN author in his own right, and one of the longest serving technical instructors on Wi-Fi there is, David devoted his own precious time to his review of the manuscript. I can’t figure out where he found the time, since David is one of the few people who travels more than I do.

Joe Fraher

Joe is simply the best tech writer I know in the networking industry, and granted my request for a review without hesitation. When I write, I have a large supporting cast at O’Reilly who take my draft work and turn it into something professional. When Joe writes, he does everything himself, including the illustrations. For a long time, he even had the unthinkable task of producing all of Aerohive’s documentation himself.

Craig Mathias

Craig is one of the best-known wireless LAN analysts in the industry. He has been a champion of the first edition of my book since it came out a decade ago, and I was happy that he took the chance to correct this book before publication.

Bob O’Hara

Bob was the original technical editor of the 802.11 standard when it came out, and he later co-founded the wireless LAN company Airespace. He graciously gave his time and shared a great deal of historical knowledge about why 802.11 is designed the way it is.

Changming Liu

When he started Aerohive, Changming went all-in on 802.11n as the future of both wireless LANs and his newborn company. In addition to being dead right about 802.11n, he is a person that I learn something from every time I talk with him. I only wish that I’d had more opportunities to learn from him in the past two years.

Andrew von Nagy

Andrew is the wireless architect at a major retailer, and creates incredibly deep and detail-oriented posts on the technology at Revolution Wi-Fi. In building a network, you have to blend the theoretical knowledge of the protocol with practical expertise in how equipment works. Andrew contributed commentary based on living, breathing network deployment every day.

Adrian Stephens

Adrian knows 802.11 as well as anybody I know, with the added benefit that he can explain almost any detail better than anybody else alive. Adrian gets around Cambridge by bicycle, and it is a long-running item of gallows humor in the 802.11 working group that a bus driver in Cambridge having a bad day could easily set back the 802.11 standards effort years by hitting the wrong person. I am indebted to Adrian for his guidance when I served as chair of the 802.11 revision task group, as well as for the foreword.

Tim Zimmerman

Tim was present at the creation of 802.11. He was a voting member of the working group that approved the first published 802.11 specification, and he was involved in an organization called the Wireless LAN Association, which became the Wi-Fi Alliance. Few people can combine deep historical knowledge with a broad sweep of knowledge across an industry from the vantage point of an analyst.

In addition to the formal review team, I benefited from the assistance of several others.

Many companies treat authors with suspicion, if not outright hostility, and I am lucky that Aerohive is an exception to this practice. Adam Conway, my boss, immediately supported my book proposal, even though having one of his employees write a book was a novel experience for him. Aerohive’s marketing team was a source of repeated encouragement throughout the process; I would specifically like to recognize Stephen Philip, Zena Baloca, and Jenni Adair for their many motivational conversations during the book’s gestation.

Terry Simons, a talented test engineer for a major Wi-Fi player, was a never-ending source of commentary and suggestions—and I mean that in a good way! Chris Hessing never fails to inspire me to learn more about technology, and offered to read this book before I asked.

I owe special thanks to the Wi-Fi Alliance’s marketing staff. Kelly Davis-Felner was incredibly responsive to my permission requests. My day-to-day work as a task group leader at the Wi-Fi Alliance has been ably supported by both Sarah Morris and Kevin Robinson, both of whom contribute to the industry in ways too innumerable to list here.