Though this book presents a fair amount of theory, we have gone to great lengths to keep the material as practical as possible. It has been written so that you can read a chapter, apply that chapter, and come back to learn more. IT professionals, a large piece of this book's target audience, are often the type of people who learn best by doing , so that's how the material is presented. In fact, you'll notice that the book looks at telephony more from a packet networking engineer's perspective than from a telephone network engineer's perspective, even going so far as to apply the OSI model to telephone systems, which were invented decades before the OSI model was.
But anybody who's new to VoIP should get a handle on its terminologies, implications, and scope by reading this book. IT managers, telecommunications directors, and hands-on CIOs will all benefit from the proper (and one might say refreshing) perspective this book has toward Voice over IPnot the textbook perspective of a legacy telephone system engineer, but the hands-on viewpoint of an IP networking pro who recently completed a number of legacy-to-VoIP system conversions. In this case, it can truly be said that I am cast from the same mold as my readers.
Prospective VoIP adopters, Cisco-certified network specialists, and those with a persuasion toward open standards may want to read this book on account of its vendor neutrality. Linux, Windows, and Mac solutions are discussed, while Cisco, Grandstream, Digium, and other hardware vendors play prominent roles in the hands-on projects. This is no accident . The world of telephony is a multivendor domain in which interoperability is critical and failure of competing vendors ' systems to work together, unlike desktop computing, is unacceptable. This book therefore advocates strongly for international standards ratified by the International Telecommunications Union, the Internet Engineering Task Force, and other bodies.
Asterisk is an open source telephony server that runs on Linux, FreeBSD, and Mac OS X. It was chosen as a platform for illustrating many of the examples in this book for several reasons. It supports many of the standards needed to teach VoIP signaling concepts; it runs on regular, easy-to-get PC equipment; and perhaps most importantly, it's free. If you want to experiment with VoIP without spending a lot on hardware, Asterisk is a great starting point. And while commercial solutions have their place, you might also find that Asterisk is a worthwhile end solution. You'll find a partial Asterisk reference and appendixes at the end of the book.