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Practical VoIP Using VOCAL by Luan Dang, Cullen Jennings, David Kelly

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This book is the product of a Silicon Valley success story called Vovida Networks, a high-technology start-up founded by Alan Knitowski and Luan Dang. Vovida recruited an international team of talented developers to build an open source (http://www.opensource.org) phone system that became known as the Vovida Open Communication Application Library (VOCAL). Vovida’s aim was to enable a community of developers to produce new Voice over IP (VoIP) applications that would challenge the established companies, dispel popular beliefs about phone systems, and contribute to a new world of interactivity and interoperability. All of the technololgy that Vovida built is open source. You can build a complete phone system from it, and this book describes how to acquire, compile, install, and work with the applications as an end user, and how to work with the code as a developer.

During the time that Vovida was building its team and developing its applications, the industry was going through an exciting period of growth and innovation. The Telecommunications Act of 1996 (http://www.fcc.gov/telecom.html) had opened up a previously closed industry to “...promote competition and reduce regulation in order to secure lower prices and higher quality services for American telecommunications consumers and encourage the rapid deployment of new telecommunications technologies.” At the same time, many venture capital firms had relaxed their guidelines about lending and initial public offerings (IPOs). This mixture of new law and new money helped establish more than 1000 new telecom service providers, along with many new software and hardware manufacturers. A strong stock market also permitted established organizations to expand their capabilities by acquiring innovative start-ups.

At the height of this prosperity, Vovida Networks was acquired by Cisco Systems, which enabled VOCAL and a new web site called http://Vovida.org (http://www.vovida.org) to continue growing and expanding their communities. VOCAL is currently being developed not only at Cisco, but also inside the laboratories, cubicles, and basements of community members scattered throughout the world. http://Vovida.org is a communications community site dedicated to providing a forum for open source software used in datacom and telecom environments. From April 2001 to January 2002, the number of downloads of VOCAL source code[1] grew from 697 to 1293 per month, almost a 100% increase in 10 months, demonstrating the steady momentum of the open source movement in Voice over IP.

Whether it is through the mailing lists, from meeting developers at different trade shows, or from talking directly to people who have worked with VOCAL in their corporate labs, we hear a consistent story coming from the community: those who have built their projects on top of VOCAL components, rather than from scratch, have significantly reduced their development costs and time to market.

We want you to share in our success by creating the next killer application, hosting a friends and family phone system at home, or finding another creative outlet that satisfies your curiosity about VoIP. We look forward to receiving your messages on our mailing lists as we hope to find out more about your experiences with running VOCAL.

How to Use This Book

This book has been written to appeal to three types of VOCAL users:


One who is interested in using VOCAL as a small phone system, who may make some minor code changes but has no interest in turning it into a commercially viable product

System administrator

One who has been tasked to maintain a VOCAL-based phone system but who has no interest in VoIP software development

Professional developer

One who is using VOCAL to test commercial applications or who is building new commercial applications on top of the VOCAL source code

Here are some suggestions about how each type of user can get the most out of this book:


Use the instructions in Chapter 2 to install VOCAL onto a single host and to test your installation, and then refer to Chapters 4, 5, and 6 for information about working with users, dial plans, and servers. Refer to Chapter 8 to learn about the SIP stack architecture and Chapter 9 to learn about the base code. Afterward, refer to the chapters from the second half of the book for more information about the other VOCAL modules.

System administrator

Refer to Chapters 2 and 3 for information about installing VOCAL and configuring IP phones and gateways, and then refer to Chapters 4, 5, and 6 for information about provisioning users, dial plans, and servers.


Refer to Chapter 2 about installing VOCAL; refer to Chapters 4, 5, and 6 about provisioning users, dial plans, and servers; and then refer to the chapters in the rest of the book that best suit your needs.

[1] There is no correlation between number of downloads and active VOCAL systems. Any given person could download one copy of VOCAL over another or could run multiple systems from a single download. However, the growth in the monthly number of downloads is a strong indication of the growth of the community.

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