transition, this book will help you implement it. The organization of the book arranges the content into three easy-to-use sections at suc- cessive levels of detail and an increasingly closer look at the actual implementation of the network. The first part provides guidance and overview material, the second part offers hands-on, in-the-trenches planning information, and the last part provides configuration examples for network implementation. This book is a practical guide for migrating your network to incorporate SIP trunking for PSTN access. It addresses questions such as: What is a SIP trunk, and why should I care about it for my network? What are the components of a SIP trunk solution? How much can I expect a SIP trunk to save me on my communications bill? How do I determine which service provider's offering to go with? What does SIP trunking mean to the way calls flow in my network between my data centers and remote offices? What does SIP trunking mean to my dial plan? What security issues does a SIP trunk expose my network to? How do I configure the extensive features required to implement a successful SIP trunk? Who Should Read This Book? This book is a roadmap to help you understand the path toward rich end-to-end commu- nications using SIP. Part I of this book is helpful if you want to learn about the communications industry trends and direction. It provides an overview of the TDM to SIP transition at a high, easy- to-grasp level with a handy cost-analysis right up front. Part II should be read if you are responsible for the planning and design of a network migration for your company or for your customer's network. It is also helpful if you are doing the service provider evaluation for bringing in a SIP trunk. Part III is helpful to the network engineers and implementers who configure the network equipment that carries calls to and from SIP trunks. This book is not designed to be a general networking topic book; a certain familiarity and level of experience with SIP and unified communications are assumed