This book explains in clear, unambiguous terms the meaning of quality of service and how to develop an infrastructure that will provide this elusive characteristic. More importantly, it provides a vendor-independent view of network performance and capacity management.
I particularly liked how the author distinguished between quality of service (QoS) and classes of service - these are important distinctions that will influence how you develop strategies for achieving either or both.
The heart of this book is the section titled Performance Toolkit. The clear explanations of all of the "moving parts" at the physical and protocol layers are the best I have ever read. These were augmented by illustrations that effectively conveyed conplex information and interrelationships without confusing the reader. Most of the illustrations have two basic elements: a physical or logical network diagram on top, with timing or interaction information below. This, in my opinion, is one of the key strengths of the book because I was able to immediately understand what the author was trying to convey.
In addition to a structured approach to QoS the book is also sprinkled with interesting information that is set in text boxes. Examples are web links to additional information, interesting discussions that support the main text (I loved the discussion on the "Speed of Light Problem"), and anecdotal information that liven up the book.
After reading this book I felt I had not only a firm grasp on what it takes to achieve QoS, but that I also understood with a great deal of clarity how networks work at the physical and protocol layers. This alone speaks highly of the book because I have more than 12 years of network experience.
Regardless of whether you are working towards or are certified in a particular vendor technology (i.e., MCSE, CCIE, etc.), this book will expand your knowledge of networking in general and QoS in particular.
If you are a network architect this book with provide you with a strong foundation upon which you can build a solid QoS strategy. It also gives a sound approach to performance and capacity management, which would be nicely augmented by either (or both) of the following books: Capacity Planning for Web Performance, and Scaling for E-Business, both by Daniel A. Menasce and Virgilio A. F. Almeida.