Preface

This book is a sequel to Building Telephony Systems with Asterisk, which started you on a journey to the summit of Asterisk knowledge, taking you from base camp to camp two, from being a complete Asterisk newbie to a competent telephony system builder and manager. Now it's time to push to the top, to take your telephony knowledge to a point where you can build high-performance, resilient, and professional PBXs using the most popular open source telephony software in the world—Asterisk.

In that book, the focus was very much on installing and configuring Asterisk for a number of common scenarios, including both home and office use. This it achieved admirably, so you may now wonder why another book is needed. Well, there are three main reasons for writing this book. Firstly, Asterisk is such a highly-capable and configurable telephony engine that the 150-odd pages in the book necessarily had to exclude discussion of some of the more advanced features, which we now have the opportunity to explore. Secondly, Asterisk is invariably implemented as part of an IP network, and further examination of network considerations is warranted. Finally, like all popular open source software, Asterisk is constantly being updated, and while this book still assumes the version 1.4 of Asterisk is in use, we do point out any differences in version 1.6 where relevant, such as the change from Zaptel to DAHDI.

Therefore, the goal of this book is to give you enough knowledge to build and install a telephony system with Asterisk at its core, which will stand comparison with the market-leading commercial IP-enabled systems. Whether you are building such a system as a result of an internal company requirement, or you plan to offer it as an element of a commercial package to customers, this book will take you through all the areas that require consideration. On reading this book you will also be in a position to understand the real-life issues you are likely to experience when deploying such a system, both technical and otherwise.

By its very nature, Asterisk demands that much of the focus of this book be on the technical aspects of building your professional system. However, as with most IT implementations, success will also rely on "soft" issues such as managing expectations, understanding and meeting the customer's particular needs, and ensuring delivery is on time and up to the budget. Hence, where appropriate, we make mention of the non-technical aspects that may make a difference to your deployment.

To achieve our goal, this book will build on knowledge already gained by reinforcing that learning and adding extra skills covering: