This is the Preface Excerpted from the Book, Switching to VoIP, by Ted Wallingford

Here's another excerpt.

Originally published by and (C) 2005 O'Reilly Media.

Voice over IP is a family of technologies that addresses enterprise networking, human interaction, audio and video transmission, and business management. VoIP, as its abbreviated, has sweeping implications for everybody who uses telephones, the Internet, FAX machines, e-mail, and the Web. VoIP borrows from, and enhances, many disciplines of communication technology. Internet Protocol, analog telephony, digital telephony and T1 circuits, digital audio signal processing, high-availability networking and a host of other concerns are all touched by growing borders of the vast, ambitious realm of VoIP.

VoIP has found its way into business phone systems, desktop messaging software, and residential telephony service. Your mortgage or insurance company's web site may now offer you the ability to communicate by VoIP with a customer service rep using your computer. Or, you may subscribe to VoIP-based telephone services like Packet8, AT&T CallVantage, or Broadvox Direct as a replacement to your old, traditional phone service.

In the late 1990s, VoIP was lauded as a way to save on long distance charges by calling grandma and grandpa using a PC with a headset and a microphone. But today's definition of VoIP is far broader, and certainly more important. Hundreds of thousands of VoIP-based devices are in use in the United States, and fast-growing shipments of VoIP-compatible telephone systems have revitalized the data-networking industry, creating the next evolutionary step for the Internet and IP networks: Making Internet Protocol and its physical-layer counterparts robust and reliable enough to replace the global telephone network as we know it.

So, VoIP is a disruptive technology family that promises to revolutionize the way we communicate, while driving decreases in the cost of that communication, and increases in the speed, reliability, and availability of the Internet itself. That's what VoIP does. But you're reading this book because you want to know how it does it. Here's what you'll encounter while reading Switching to VoIP:

o A basic definition of public and private legacy voice systems, and a quick review of their evolution.
o A moderately detailed description of the core technologies of digital telephony--sampling, pulse code modulation, time division multiplexing, trunking, and call-signaling.
o Examples of how VoIP networks overlay IP networks, and how voice applications reside within the OSI network model.
o An explanation of why many early VoIP adopters' implementations didn't live up to their expectations.
o An introduction to the two subsets of VoIP protocols: audio transmission and signaling.
o Introductions to SIP, H.323, and other signaling specifications that are commonly used in IP telephony.
o Some practical strategies for justifying VoIP adoption in a business scenario.
o An introduction to IP hard phones, Analog Telephone Adapters, softPBX servers, and the other devices that make VoIP systems tick.
o Strategies for dealing with quality of service issues, including policy-based, protocol-based, and practice-based approaches to ensuring tip-top operational quality of a VoIP network.
o Information about interfacing VoIP systems with traditional phone equipment and the public telephone system by way of analog trunks and T1 lines.
o The basics of enforcing low-layer security in a VoIP environment, with examples for IP Tables firewalls.
o Tips for gauging VoIP readiness on an enterprise network, or over an Internet pathway.
o Scenarios that describe what network technologies work best for voice systems, and how to compensate with quality of service measures across those that don't work so well for voice.
o Dozens of practical, hands-on projects that you can use to build the pieces of your VoIP network while learning which standards and practices will work best for your particular environment.
o A number of troubleshooting scenarios to will help you deal with, and avoid, the most common mistakes that are made when implementing this technology.
o A handy vendor reference that will put you in touch with the key software, hardware, and service players in the VoIP business.
o A reference for the basic configuration, SIP interfacing, and legacy interfacing of the world's most popular open-source telephone server, Asterisk.

Audience

Though this book presents a fair amount of theory, it has 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. I.T. 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 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. I.T. managers, telecommunications directors, and hands-on CIOs will all benefit from the proper (and one might say refreshing) perspective this book has towards Voice over IP--not 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 the author was cast from the same mold as his readers.

Prospective VoIP adopters, Cisco-certified network specialists, and those with a persuasion towards 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 multi-vendor domain where 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.

Regarding Asterisk

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. You'll find a partial Asterisk reference and appendices at the end of the book.

Assumptions Made in This Book

Some familiarity with data networking is assumed. A basic review of TCP/IP addressing and the seven-layer OSI network model is included, but proceed with caution if you aren't already accustomed to these conventions. Each chapter builds upon the concepts described in the previous chapters, so the book is intended to be read in order.

Where to Get More

There are 1000-page books about telephone systems, and there are 50-page reference pamphlets about a single protocol, like SIP. When writing a book like this, it's a challenge to strike a balance between the unwieldy tome that's filled with countless details of trivial import, and a crash-course FAQ that tells you just enough to get started. On one hand, there's nebulous reference material, and on the other, there's not enough detail but lots of conciseness.

To address this, the book is rather detailed on certain subjects, and rather brief and concise on others. If you're looking for more information in a special area, O'Reilly offers other books that may help you, including narrow but detailed books about T1 circuits, data-communications theory, network security, and Ethernet. Safari Online is O'Reilly's web-based library of books, an invaluable tool that can also provide more depth. Both O'Reilly's printed books and Safari are available at http:///www.oreillynet.com.

Acknowledgements

My first non-curricular writing was a short science fiction story I wrote after having been inspired by my third-grade teacher's reading aloud to my class. The book he read to us was The Lion, the Witch, and the Wardrobe by C.S. Lewis. So, I owe a Thank You to Mr. Dennis Streich, my third-grade teacher, for giving me a respect for the social and educational importance of the medium of books. While I can't blame any of my bad writing habits on these two gentlemen, I can certainly credit them with helping to cultivate my love of the written word--even when it's about a geeky subject like VoIP.

More recently, my reading and writing have been of an entirely different sort--the vocational sort. When I worked for J. Walter Thompson in Detroit, I was flipped a copy of O'Reilly Media's epic masterpiece Sendmail by one of the guys I worked with. This book was a godsend. If anybody could translate a deadly topic like Sendmail configuration into terms I could understand, it was Rickert, Costales, and Allman, the authors of that highly important book. The accessibility and organic approach of Sendmail were common to most O'Reilly books, I later noticed. Whether it was Practical PostgreSQL or RealBASIC: The Definitive Guide, I had an easier time learning from these “animal books” than I had from others.

When given the opportunity to write about Voice over IP for O'Reilly, it was an easy decision. I had just completed the first phase of an ambitious telephony conversion on a large construction contractor's network, and I was looking for standards-advocating documentation to help me architect the next phase. The problem was, all the decision-making intelligence for my project was provided by the VoIP equipment vendors and their salespeople--Cisco, Avaya, Nortel, Mitel, NEC, and so on. Cisco was bashing Avaya, and Avaya was bashing Nortel, ad nauseum. I was looking for the neutral, standards-respecting VoIP authority in book form, and I couldn't find it. So I decided to write it myself, more or less as an exercise to aide my project. Fortunately, Tim O'Reilly and Mike Loukides, the editor of this book, thought it would be a good book to publish.

I learned a lot about VoIP while writing this book, and I hope it engages you in the subject as much as the writing process engaged me in it. VoIP is a technology family that I feel very passionately about. It has the legitimate potential to truly revolutionize distance communication. VoIP is an expression of the Internet's promise of allowing better, faster, more accurate communication between people, and it's a culturally-impactful next step for the international telephone system. In other words, Voice Over IP is important. It is becoming a sustaining technology due to the growing adoption of enthusiastic implementers such as you and I. My sincerest hope is that this book provides you with an arsenal of fair, even-handed technical information and advice that will help you succeed in building your VoIP systems.

Switching to VoIP was made possible only with the efforts of quite a few contributors, from editorial supervision to illustrators to technical reviewers. In particular, Mike Loukides, this book's editor, kept me focused like a laser on the things that mattered, and steered me away from the things that didn't (like my original proposal for a detailed description of the telegraph). Interesting--sure. But not at all useful. The technical reviewers who participated were outstanding as well. Every one of them a master of gracious criticism, the review team improved this book immensely, fixing my technical faux pa, and offering ideas I hadn't even thought of. The review team included these immensely talented networking pros: Bernard Hayes, Ryan Courtnage, Jason Becker, Rich Adamson, Jim Van Meggelen, Jason Gintert, Jared Smith, and Todd Nathan.