Introduction

Ever since Alexander Graham Bell invented the telephone in 1876, telephony systems have been a part of our life. More recently, with the advent of the Internet, much of our day-to-day communication (for example, e-mail) crosses an IP network (for example, the Internet). Today, these two worlds are merging, and companies can place phone calls over their existing data network infrastructures using a technology called Voice over IP (VoIP).

The topic of VoIP attracts people of diverse backgrounds, from the private branch exchange (PBX) technician, to the network engineer, to the home user wanting to reduce his or her monthly phone bill. This book gets all readers on the same page by reviewing legacy telephony systems, and then it proceeds to delve into the brave new world of VoIP.

When I teach VoIP courses, I use plenty of metaphors to help anchor what can be complex concepts. The format of the Cisco Press First-Step Series allows me to talk with you and share stories, just as if you were attending one of my classes. So, expect plenty of metaphors, analogies, and even a little humor. Also, if you're like me, you learn best from examples. So, I've sprinkled multiple case studies and other examples throughout this book.