This book explains why people and companies are using SIP based IP Telephony equipment and software to efficiently upgrade existing telephone systems, develop their own advanced communications services, and to more easily integrate telephone network with company information systems. SIP technology is a well-established standardized communication protocol that has many low cost devices and software application development tools available. The use of SIP product and software allows companies to cost-effectively upgrade and eventually replace existing (legacy) telephone systems with more cost effective and easy to use telephone equipment. Because SIP is a standardized protocol, this allows end-users and system administrators to have more control and even develop communication services (such as smart voice mail) that have been traditionally been unchangeable and limited. SIP is a text-based protocol (similar to web HTML) and this allows for relatively easy development and integration with existing company information systems to produce new revenue producing services (such as integrating telephone and order processing systems). Although SIP is an industry standard, not all SIP systems and services are the same. There are cost and quality tradeoffs along with common problem areas and risks. There are many ways SIP systems can reduce telecommunication costs along with the ability to create new revenue producing services. This book will help you to understand what SIP is, how it operates, what services it can provide, and your company can benefit from implementing SIP. Some of the most important topics featured are: - Descriptions of the function parts of SIP systems - Fundamentals of how SIP works - What key services are possible through the use of SIP - How existing phone systems can be upgraded to SIP capabilities - Why it is easy to integrate SIP with information systems - How to develop new advanced revenue producing services - The basic SIP system development process - How to manage SIP systems - Typical costs of SIP systems - How SIP is changing