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Asterisk: The Future of Telephony

Leif Madsen, Jared Smith and Jim Van Meggelen
Published by O'Reilly Media
ISBN:978-0-596-51048-0
602 pages
£ 27.99
Published: September 2007
reviewed by Raza Rizvi
   in the December 2007 issue (pdf), (html)
bookcover  

Two years separates the first and second editions of this book and in this time the breadth and capabilities of Asterisk have increased massively. By all accounts this is shown in the size of this second edition which is nearly double the length of the first (this edition covers the current version 1.4 so it isn't out of date yet!).

Presuming no prior knowledge of Asterisk but a basic understanding of Linux (the examples use Red Hat) the book does a reasonable job of leading one through to complicated PBX programming topics. Much of the information can be found online but the collation into a single volume will clearly aid those responsible for the installation, administration, and maintenance of any reasonable sized deployment.

Starting at the beginning then, we are lead through the reasons why Asterisk came about in the first place, and the flexibility such a softPBX gives the end user. There are some sensible and admittedly obvious recommendations for the hardware environment for hosting the (normally business critical) telephony platform, and then a run down of the Red Hat installation procedure.

We now, in chapter 4, start the actual configuration of the server software itself for the combinations of analogue or SIP handsets, and pleasingly there are details of connecting two Asterisk boxes via both SIP and IAX (the originally Asterisk specific VOIP based protocol). Details of selecting, creating and extending a dialplan are given in the next two chapters. These tell Asterisk what to do when it sees a string of digits...

Chapters 7 and 8, perhaps rather lately in a book that starts with no requirement to have knowledge of telephony, describe what happens to place and receive a call in the traditional and VOIP environments. On first reading I had expected these to be the initial chapters but in hindsight, one doesn't actually need to know any of this in order to get an Asterisk server up and running, and perhaps that shows why this is a book aimed at administrators rather than being a academic reference text just using Asterisk as an example.

Programmatic interfaces are covered from chapter 9 to 12 and again they seem out of sequence because one has to wait until chapter 13 (and partially chapter 14) before the system administration are (too briefly) covered.

There is naturally a bias to number examples following US style sequences but the examples do seem easily convertible to UK style numbers. More difficult might be the assumption that one would be happy with the default US style ringtones and sound files -- hint: one can get some from http://www.tel.net/voice.html

Elsewhere the book does recognise it will get read in Europe and there are references to E1 circuits and suppliers of suitable equipment.

Whilst I spotted no errors on my initials trawls through the book I note that (trivially) the initial paragraph from the Colophon section is at the end of the details for Madsen in the `About the Authors' section. Things will move on a pace and readers would be wise to check online at the release notes for whichever dot-version of Asterisk they install to see what the latest changes to configuration or coding are.

To my mind the book would actually be better split into two for the administrator and programmer audiences even though there would be many chapters in common at the start. This would have also meant that the long appendices could be segregated to the correct readership. I would have liked to see more information on the administration of the system and perhaps at least an acknowledgement that one might interact with Asterisk as a managed solution run by a service provider `in the cloud'. There is very little about the role that ENUM (simply put, phone number mapping onto DNS) will play in placing incoming communications. That said, there are plenty of pointers to places on the net to assist the reader and the layout is typically clear and easy to read, and for that I recommend the text to those who are planning to dabble with Asterisk.

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