Thanks to Flavio E. Goncalves, a new edition of "Building Telephony Systems with OpenSIPS" is available. It covers the latest stable release, the OpenSIPS 1.6, updating existing topics (NAT traversal, Accounting, etc) , but also approaching new 1.6 specific technologies (using caching, dialogs, etc).
The book teach you how to build scalable and robust telephony systems using SIP
* Build a VoIP Provider based on the SIP Protocol
* Cater to scores of subscribers efficiently with a robust telephony system based in pure SIP
* Gain a competitive edge using the most scalable VoIP technology
* Learn how to avoid pitfalls using precise billing
* Packed with rich practical examples and case studies on the latest OpenSIPS version 1.6