I've bought and enjoyed some of the author's other books (ATM Theory and Applications and QoS & Traffic Management), but was a little bit disappointed in this one.
Instead of being a book about VPN-specific technologies (things like IPsec, etc.), most of this book reads like a general overview of voice/data communications technology. Topics like SS7, VoIP, AIN, etc. as well as introductory coverage of things like IP, Frame Relay, ATM, etc. fill most of the book. Unfortunately, the coverage is pretty light, so it's not really suitable as an introductory text or for experienced network engineers (despite a few fairly math-heavy pages).
While I suppose a case could be made (and the author does try to make it) that these topics are the building blocks of VPNs, it seemed that a lot of this material was included just to fill up the book -- the mandatory OSI model chapter is now being replaced by the mandatory TCP synchronization/RED chapter and this book is no exception.
It's disappointing to get a book on VPN only to find that 80%+ of it has almost nothing to do with VPN's in particular. As usual, McDysan does an excellent job presenting the information, it's just not the information I had expected. The Wiley "Implementing IPsec" book is a much better reference if you're interested in the security aspects of VPNs.
(In all fairness, this "general technology padding" isn't unique to this book -- it seems that almost all of the 20+ technical books I read a month are part of this disturbing trend. With the (literally) hundreds of books on the market about things like IP, routing, etc., there's really no excuse for filling speciality books with technical tutorials).
