For those who haven't heard of Asterisk, I like to describe it as "all things 'phone' for the Linux geek." The offical site describes it as "a complete PBX in software." Up until now, the best way to find information about Asterisk was wading though a very high traffic mailing list or browsing a good, but ever changing wiki dedicated to the subject. A few times I've even resorted to reading the project's source code looking for answers to my questions about configuring Asterisk. O'Reilly's book Asterisk: The Future of Telephony goes along way toward filling the void of good documentation on the software PBX.

One of the things that makes it hard to get started with Asterisk is figuring out what it is and what it can do. For those who may still be wondering exactly what Asterisk is or does, I quote further from the official site:

Asterisk is a complete PBX in software. It runs on Linux, BSD and MacOSX and provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in many protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware.

Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response and Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway). Check the Features section for a more complete list.

That's a mouthful. Don't worry too much if that adds to the confusion, the book will help you get it all figured out.

I've been playing with Asterisk for a little over a year. It's hard to remember how just how steep the learning curve was. Most Asterisk newcomers are probably a bit like I was. I had some Linux sysadmin experience but was new to voice, telephones and VoIP. The idea of being able to use cheap (relatively speaking), commodity hardware and Open Source software to run my small office phone system was very appealing. This book will help any such Asterisk newcomer do exactly that - and much more.

In all honesty (and in the spirit of full disclosure), one of the coauthors of the book is a casual acquaintance of mine. I would email him for help when I got stuck on an Asterisk or VoIP concept and he would point me in the right direction. I feel like this book is an extension (ouch, bad Asterisk pun) of that relationship; I still get the answers I need, but now, I get them faster, with less begging and I get them in print :) .

Asterisk: The Future of Telephony sports a bold title. The point is reinforced in the first chapter "A Telephony Revolution" and picked up again in the last chapter that sports the same name as the title of the book. These few pages focus on making the case that Asterisk is, and will be a disruptive force in telephony. I believe that. My favorite line in the whole book, "Telecommunication companies who choose to ignore Asterisk do so at their peril" comes from the first chapter. Between these bookends are nine additional well written chapters that will help you pick the right hardware, get Asterisk installed, configure the basics, tweak it to your needs and learn a few advanced tricks.

They do something interesting in this book, something unexpected. They hold off on priming you with the basics of telephony until Chapter 7 after you get Asterisk installed and mostly configured. This is a good approach. That kinda thing might bore Linux sysadmins. All we want to do is breakout the shell and get hacking! After we have our fun, it's time to sit down and learn the nuts and bolts of the telephone system.

Chapters 4, 5 and 6 are where most Asterisk newcomers will find themselves spending time, reading and rereading. There you will learn, in a straight forward manner, how to get Asterisk working with your system and behaving as you would like. The core of your new phone system is the "dialplan." Dialplans can range from very simple to extraordinarily complex. The authors of the book realize this and give you two chapters (5 & 6) covering topic in various depths.

The fun stuff comes in the last few chapters. Here you will learn how to hack Asterisk using AGI (the Asterisk Gateway Interface) and other advanced topics. If the book has a fault, it would be not making these chapters into their own section and really beefing them up. For example, I would have enjoyed more information on the Manager Interface.

I've read quite a few technical books in the past and have developed a few pet-peeves about them. In no particular order they are: bad editing, lame illustrations for the sake of having them, overly lengthy code listings used as filler, weak or nonexistent appendixes and selling other books in the footnotes.

Asterisk: The Future of Telephony suffers from none of these. The book is very well done and lives up to O'Reilly's deserved reputation for quality. The book does contain a few well placed suggested readings which are not limited to the publisher's offerings. It also uses appropriate file and code listings. That's a hard one to get just right, but the authors seem to strike a good balance. All 5 appendixes are thorough references and add real value to the book.

In case you had not guessed it, I strongly recommend this book. Between the time I first read the text and actually wrote this review, I had a discussion with someone who was getting into Asterisk for the first time. They had tons of questions for me which I happily answered (like any enthusiastic geek might). When I suggested he pick up a copy of the book, he replied that it wouldn't be necessary because all of the information was available on the Internet. He may have been right, but clearly he failed to find it! Asterisk: The Future of Telephony is simply a must for anyone getting into Asterisk

gundy dot org is Gabriel Gunderson's blog about stuff and things. You can also find additional Asterisk resources at his site.