Why I Ask Why (And My Review of Matthew Gast's 802.11ac Book)

802.11ac: A Survival Guide is a recently published handbook about 802.11ac.  The author is Matthew Gast, a very knowledgeable WiFi guy who follows the IEEE 802.11 Working Group closely.  I recommend the book if you work in WiFi.  It is informative.  There is great attention to detail.  All areas of the subject are covered.  But I was left uninspired.  And my uninspiration (is that a word?) was the result of the book being short on something that I always hope to find in any technical writing: the Why.

In some ways yours truly is the target audience for the book and in some ways I'm not.  I need to know the intricate details of how WiFi works.  (Point)  I already knew most of the tweaks that 802.11ac is making to 802.11n.  (Counterpoint)

The physical layer is the most important part of 802.11ac, and that is where this book wins.  For example, before I read the book I was unaware that 802.11ac allows devices with different channel bonding capabilities can access a wider channel at the same time.  That's a big deal.  One of my criticisms of 40 MHz channels in 802.11n is that channel space is wasted.  If a device that is only capable of using a 20 MHz channel wins arbitration, then the unused 20 MHz stays vacant.  That's a waste.  If you use an 80 MHz channel in 802.11ac, two 40 MHz-capable devices can use the channel simultaneously (with a small amount of dead time on one of the 40 MHz spaces), thus keeping the available RF efficient.  Matthew Gast not only explains that concept clearly, but he has great graphics to aid learning.

Unfortunately, the book itself struggles in keeping things efficient.  For example, during the MAC layer chapter the explanation of QoS rambles.  If you understand 802.11e QoS and you understand MU-MIMO, then there's a 99% chance that you understand MU-MIMO QoS without it being explained to you.  If an AP has frames with varying WMM priority levels ready to send to multiple devices using MU-MIMO, then the lower priority frames are allowed to piggyback on the higher priority frame's channel time.  That makes sense.  And it makes sense that lower priority frames that would take more channel time than the higher priority MU-MIMO frame are not allowed to piggyback.  It's a concept that takes a couple of sentences to understand.  In the book it takes two and half pages.

The fundamental reason why the book gets flabby at times is because it could use a little more focus on the Why.  For example, it's great to list all of the different PHY header fields and options.  But tell me Why first.  I want to know the spirit and the concept of why the architects of 802.11ac designed things the way they did.  Time after time I found myself reading a concept, and then stopping for several minutes to think.  I would try to envision why things are the way they are in the standard.  The book would have been richer if the author would have had that higher level view in the text.

Maybe I'm asking for too much from 802.11ac: A Survival Guide.  Maybe this book is such a technical book with such a specific audience that it should be dry and focused on the facts of the standard.  Maybe it is unnecessary for the Why to be explained.

The reason I was expecting more Why is that I believe that a broad spectrum of people care about the technical details of 802.11ac.  I believe that this book could have been made accessible to a less technical audience without turning off the hardcores.  And I believe that a lot of technical writing -- including training courses, study guides and white papers -- could be improved by a little more time being spent thinking about the Why.

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