Asterisk: The Definitive Guide, 4th Edition

Foreword

When we were thinking of who we could ask to write a foreword for the fourth edition of the book, lots of names were tossed around. We had already had Mark Spencer (author of Asterisk) write it for the first two editions of the book. Next, John Todd did a fantastic job for the third edition. After batting around several names (of which you will see below), we thought, “This is a book written by the community, how about we do a community foreword?” With that idea in mind, we picked several people whom we respect, and who have been using Asterisk as long as (if not longer than) ourselves. When we were thinking of people, we wanted to get several perspectives and loosely answer several questions about Asterisk. The questions we were looking at included:

• How has Asterisk helped in communities?

• What worldly endeavors has Asterisk contributed to?

• Where has Asterisk been and where is it going?

• Why is Asterisk being deployed and what needs does it solve?

These are all questions that most people who have used Asterisk for an extended period of time are either asked, or have asked themselves. After posing those questions to the following authors, they all came back with various viewpoints about the Asterisk software, and how it has changed the telecommunications industry and the lives of people. We hope you enjoy reading about their contributions as much as we did.

Matt Jordan (Engineering Manager, Digium)

When Leif asked me to write a foreword for the updated edition of Asterisk: The Definitive Guide, he posed the following question: “Where has Asterisk been and where is it going?” This means some prognostication is ahead—you’ve been warned!

To answer the first part, I looked at how Asterisk has evolved over the past several versions. Each version has built upon the previous in an iterative fashion, while still remaining true to what made Asterisk great: a free and open source platform to build telephony applications. As time passed and the telephony landscape changed, Asterisk changed with it. Asterisk evolved with new functionality to meet the changing needs of the people who used and developed it. At times, Asterisk has pushed the telephony industry; at times it has responded to it. The result of this push and pull is the state of Asterisk today—it is in many things and in many places. It powers the phone systems of my local grocery store, drug store, and pizza chain—it is the engine of choice that powers the PBXs of everyone from hobbyists to large enterprises.

The second part is trickier. As Asterisk nears its 15^th birthday, the question in my mind isn’t so much “where is Asterisk going,” but “where is the telephony industry going?” The convergence of mobile platforms, hosted solutions, and WebRTC will fundamentally change not only our definition of a phone, but how businesses deploy their communication infrastructure and what it means to communicate. So how does Asterisk respond to fundamental shifts in deployment, operability, and usage?

In my mind, the way it always has—by being innovative. By leading the way in adopting standards for communication. By exposing new APIs that make it easier for anyone to use Asterisk to build communication applications for a wide range of business needs. And finally, by being willing to change. Asterisk has traditionally provided applications for you—if you wanted call queues, you used the Queue application. If you wanted voice mail, you used VoiceMail. As we go forward in the next major versions of Asterisk, I see the emphasis being less on providing functionality for you and more on providing the building blocks to build whatever communications functionality you need.

It is an exciting time to be a user and developer of Asterisk—and I look forward to building Asterisk with you.

Alex Balashov (Principal, Evariste Systems)

Asterisk is most often celebrated for its free licensing and its generous feature set. However, as most adopters of open source technology know, or quickly discover, it has implementation costs, too. The essential value of Asterisk does not, in my view, lie in the economic or technical efficiency of a free PBX, but in the disruptive structural effect it has had upon the larger domain of innovation in which it participates. It has irrevocably shifted the conversation about possibilities in telephony.

Asterisk did not merely offer an open source challenge to incumbent PBX vendors. The fact that it could run on commodity PC hardware and small, PC-compatible embedded devices set off a tectonic shift toward the commoditization of business problems that were previously solvable only by complex data interchange performed on expensive, proprietary hardware or expensively licensed software, such as, for instance, interactive voice response (IVR) systems that provide self-service interfaces to banks. Asterisk has numerous integration pathways and APIs that allow it to connect to other commodity services using open standards and ubiquitous protocols, drastically lowering the cost of making it talk to other systems. It is impossible to overstate the transformative impact this has had, enabling entirely new business models to take flight, untethered by hitherto prohibitive capital drag.

Asterisk can take credit for the fact that there are now entirely new, generational answers to the question, “can we make the phone system do this?” Incumbent telecom vendors, irrespective of the degree to which they view Asterisk as a competitor, have had to re-frame their marketing message in terms of the possibilities that it has forced open. Asterisk has changed the observational language—the vocabulary, the thought process, the basic economic assumptions—of business telephony systems.

Asterisk’s interoperability and attachment to commodity hardware has also weakened the walls of formidable fortresses of telecom monopoly that were previously thought impregnable. I have witnessed its use with libss7 as an interconnection element by competitive operators in several emerging-market countries, and as the backbone of toll bypass applications and cost-efficient calling card services. The impact of this Asterisk-driven pressure wave of innovative, low-cost alternatives is titanic, having created entirely new social connections, jobs, and livelihoods around the world, enriching the lives of many people. My own family is scattered around the globe, and my Asterisk PBX has made that world a whole lot smaller. We simply could not afford to communicate so closely, regularly, and richly before.

In sum, I think that in the overall continuum of technological development, Asterisk may well be remembered less for what is inside of it and more for what it has shoved aside outside of it with its powerful elbows.

Kevin McAllister (VP of Engineering, CoreDial, LLC)

In the late summer of 2005 I was offered a job at a startup that planned to deliver hosted IP PBX services to businesses. At the time I knew Linux system administration, IP networking, and enough to be scared to death of voice.

The first reason for the fear of voice was that I knew how the Internet worked. Voice is the canary in the coal mine that is the Internet—when the network breaks, the voice dies first. The second reason to be afraid is that people are very familiar with phones, and therefore they have strong ideas about what phones should do to help run their business, and expect voice service to be more reliable than electricity. I would be responsible for trying to make feature after feature work under these demanding circumstances.

The plan was to build on top of an existing prototype based on Asterisk. So not only would I have the daunting task of pushing voice through my network, but also learning how to use a complex piece of open source software that traditionally offers documentation that is incomplete and often inaccurate. So the situation was I didn’t know what I wanted it to do, I didn’t know how to make the software do it, and I had no way to find out.

Luckily, there was only one book available to help at that time: Asterisk™: The Future of Telephony. That first version of this book helped me to quickly understand not only the Asterisk software, but the basics of VoIP. The presentation allowed me to see how I could quickly combine the many and very flexible features of the Asterisk software to build complex and reliable features demanded by my customers.

Now—almost eight years and countless millions of successful calls later—I have learned firsthand the things that do and do not work when building Internet VoIP systems. But I continue to rely heavily on Asterisk and on the authors of this book to help me quickly understand this constantly changing and improving software. You’ve chosen a great starting point for working with Asterisk. I wish you even more success than I have had.

Brian Capouch (Computer Science Department, Saint Joseph’s College [Indiana])

“Well, you can actually do that pretty easily.” That observation, over and over, burned itself into my brain back when I first began hacking with Asterisk. I had already been playing around—enjoying some success but suffering a lot of misery, too—with some early IP telephony products, when one day I first saw mention of Asterisk on a mailing list. I fetched the code and built it (before it was versioned!), and I’ll forever remember the first sound I heard: Allison Smith’s “Comedian Mail” voice prompt. I laughed and laughed. What was going on here??!!??

I dug in, and it changed my life. At the time, I operated a wireless ISP. It was an indescribable thrill that I was able to set up a network of Asterisk servers running on cheap eBay hardware, connected to local telco lines at fifteen POPs scattered over 500 square miles of mostly desolate Indiana farmland. I not only got my own wide-area toll-free calling zone, it was free—back in the days when minutes actually cost something.

For another project, I hooked up Asterisk and a $20 USB camera I bought on eBay, and got live video surveillance of an old railroad hotel I own in Medaryville, Indiana. It was built in 1853, and had not yet been outfitted with modern electrical service. The system ran off a marine battery that I replaced every few days.

Later on, one summer evening my friend Bob staged a faux break-in at the hotel while I was giving a late-afternoon presentation at a technical conference in faraway California. My audience and I watched the entrance door through a live feed from the camera, and before the image of Bob’s entry had refreshed on the display monitor, a portable SIP phone in my pocket rang, annunciating a “security situation” at my hotel. Asterisk servers handled the call point-to-point between the hotel and the conference center.

Asterisk is about all kinds of telephony functionality, for all kinds of situations, perfectly free for anyone to use. It’s another example of the way open source products not only save a lot of money, but do a better job than the commercial products from the big players. For me, Asterisk is about empowerment, about freedom from the dying tyranny of the greedy monopolists, and about new worlds yet to come. No matter what new communications trick you could think to try, the answer is likely, “Well, you can do that pretty easily.” This book was created by great friends who were, like me, almost present at the creation. They energetically and creatively maintain an invaluable, friendly, and comprehensive guide to one of the greatest open source products ever. Enjoy!