A few months ago I was asked by Packt Publishing to review the book "Building Telephony Systems with OpenSIPS 1.6" by Flavio E. Goncalves. They sent me a free physical copy of this book. Thanks to them for it.
Before exploring OpenSIPS, you will be taught the basics of SIP. The book will help you install OpenSIPS, and after that you'll be able to work with it. It's good for newbies who want to learn OpenSIPS from scratch.
The main part of the book explains principles needed to create an OpenSIPS routing script for real solutions. You will be able to set up authentication, integrate OpenSIPS with media server, integrate Asterisk Real Time with OpenSIPS, solve NAT traversal problems, configure accounting, and, most importantly, will understand how it works.
Unfortunately, a part of complex issues is not covered in the book. These are, primarily: building high availability solutions with OpenSIPS; SIP presence problems; MediaProxy; etc.
This book is an upgraded version of the "Building Telephony Systems with OpenSER: A step-by-step guide to building a high performance Telephony System" book. Some examples remain actual for Openser, but not for OpenSIPS. Some new OpenSIPS modules are not covered in the book. I've also found several typos in the example scripts. So, if you have problems with the examples in the book, just check the current documentation.
An excellent start to learn OpenSIPS is to read this unique book. The on-line documentation is your friend too.