Preface

We are starting a new era in the collaboration area. Voice and Video over IP are starting to dominate the world of telecommunications in a disruptive movement capable of changing the whole industry. The SIP (Session Initiation protocol) technology is at the center of this revolution. I believe, at present, SIP is the most used protocol for Voice and Video over IP.

In the future, when people learn how to use the technology, SIP will be for voice communications what email is today for text communications. We are starting with islands of SIP communications inside VoIP providers, enterprises, and even governments. In the near future, the barriers between the islands will be broken and you will be able to communicate with anyone in anyplace without paying high fees. The only fees you will pay in the future will be the access to the data network, because with the pervasiveness of VoIP and Video over IP, everything will be simply data. I remember the first days of Internets email in the early 90s. It took some years until everyone had an email address. The same thing could be happening in the SIP world now. Unfortunately, the SIP providers still behave as islands not, usually, allowing free inter-domain routing.

With the introduction of 3G, 4G, and WiMAX, fast data communications are becoming widespread in the mobile industry. Newer phones from mainstream manufacturers are starting to support WiFI, WiMAX, and obviously 3G. SIP clients can run in these platforms changing the whole mobile communication industry in the near future. Sure, the telephone companies will try, legitimately, to protect their revenue sources, but they cannot hide for ever the SIP communication infrastructure already in place. Slowly, users will start to use SIP clients in their mobile phones hugely cutting the communication costs. The movement, even without a huge sponsor, will spread by word of mouth until it becomes pervasive.

The infrastructure required for SIP communication has as its main component a "SIP Proxy" server. OpenSER is one of the best SIP Proxies in the market. It is robust, scalable, and licensed according to GNU GPL. OpenSER is now in the stage of early adopters. It is still hard to learn and to use. The idea of this book is to teach you how to implement the architecture of the SIP protocol using OpenSER. I hope this book helps you, if you are starting to learn SIP, or implement a SIP infrastructure in your company, school, or government. I wish you success in your implementations and I sincerely hope that this material helps you.