While Internet protocol (IP) telephony is very often compared to low-cost telephony over the Internet, the recent advances in quality of service (QoS) and broadband access to residential home users create a major market opportunity for service providers offering voice over IP (VoIP) services to enterprise and home users.

This book is an essential guide to the protocols underlying VoIP communications. The book covers the two major signaling protocols, session initiation protocol (SIP) and H.323, as well as the media gateway control protocol (MGCP).

Chapter 1 introduces the basics of VoIP. It covers the real-time protocol (RTP), used to transport digitally encoded voice data over packet networks, and describes how more advanced features are supported.

Chapter 2 is devoted to the H.323 signaling protocol and its associated standards, H.245, H.450, H.246, and H.235. The presentation is highly technical and detailed, and most of the concepts and protocol operations are described with examples. It is very difficult to accurately describe telecommunications protocols without ending up with complex, lengthy, and difficult-to-read material. The authors succeed in providing such an accurate description, interleaved with some historical facts about the evolution of H.323. The second major signaling protocol (SIP) comes from the Internet world. Even though it was initially considered to be a more lightweight protocol, capable of challenging H.323 and becoming an alternative for both users and companies wishing to gain share in the incumbent VoIP market, managing its current features and operational deployment requires substantial expertise and advanced knowledge.

Chapter 3 is an outstanding tutorial for SIP. The authors give a high-level overview on the origins of SIP, discuss its driving forces and the evolution of its standardization and deployment, and then describe its technical details. The logical flow of the presentation is excellent.

The fourth chapter describes how to connect VoIP with traditional telephony networks (PSTN) using MGCP.

The next two chapters address more advanced features like call redirection and network address translation (NAT) traversal. NAT devices are a major problem for any protocol based on using layer three device information (IP addresses) encapsulated at the application layer, since this information can be modified by intermediary devices (NAT firewalls) without having these changes reflected at the application layer. This chapter will be of major interest to readers needing to deploy SIP.

The book has two minor shortcomings. First, the reader is encouraged frequently to consult another book written by the same authors. Second, I wished the authors had included links to or descriptions of open source SIP/H.323 tools.

In conclusion, this book is highly recommended for a very technically oriented group of readers. The technical details and accuracy are outstanding, and those having to implement or design VoIP software will surely benefit from reading this book. Graduate students or engineers wishing to learn about the commonly encountered VoIP protocols are another possible audience for this book.