Stafford M. Signaling and Switching for Packet Telephony

Издательство Artech House, 2004, -272 pp.Off and on since 1998, we have worked on projects investigating packet voice technology. We often wished that we could find an expository introduction to the topic (especially when we were new to the subject). Our first purpose is to set forth such an exposition, focusing on architectural design of packet voice switches. We take on this task in Part I, taking care to introduce as little technical terminology as possible (and trying especially hard to avoid acronyms). We hope that this portion of the book is accessible to readers who do not have engineering backgrounds, as well as those who do.
In Part I of this book, we will see that the new paradigm draws on many areas that used to be disparate—at one time, it would have been very surprising to hear mention of data-network protocol stacks in the same breath as new voice-encoding techniques. This is no longer such an unusual juxtaposition, as these developments find common cause in next generation switching products. Our second purpose, which is served in Part II, is to provide information on some of the disparate technical areas that are such newly-acquainted bedfellows. This book is not encyclopedic and is far from being the last word on the technical topics that we cover (many of which merit entire books on their own). Our aim in introducing these topics is to flesh out the view of packet voice switches that we develop in the early part of the book. To this end we highlight essential features of each technical topic, and provide pointers to other sources for in-depth coverage. The technically-oriented portion of this book will likely be of greatest interest to readers who have engineering backgrounds. Our intention is that the prerequisites for reading this book are nonspecific, however. Many people have good knowledge of telephony but not of data networking, or extensive knowledge of data networking but not of telephony. Others may have had limited exposure to both topics, but find that they are interested in the subject of this book because they are starting to hear about Voice over Internet Protocol. We hope that technically inclined people of all stripes will find useful information here.
Last but not least, we hope to give the reader some insight regarding the difficulty of migrating from circuit-switched telephony to packet telephony. We emphasize that this difficulty is economic at least as much as it is technical; its scale has often been underestimated in the past. Throughout the book, our mindset is tilted toward large-scale deployments and interworking with existing public telephone networks.
When we were first exposed to the arguments of Sections 1.2 and 1.4, we were rarin’ to go. That was several years ago, and carriers have been very slow to adopt the new paradigm in the intervening time. Although there are many compelling plusses for packet telephony (and surely they would win the day if we were building networks from scratch), there are also many reasons why large telephone service providers’ interest in packet telephony has been tepid.
We touched on some of the barriers to migration in Section 1.5, and will elaborate on these barriers as the discussion progresses. We believe that, if we can impart a sense of the sheer enormity of the undertaking, then readers can more accurately envision the new paradigm’s road to economic viability.Part I.Switching Architectures for Packet Telephony: An Expository Description
Essentials of Next Generation Switching
Motivation for Packet Telephony Revisited
Signaling and Services
Part II. Components of Packet Telephony: Technical Descriptions
Introduction to Part II
Protocols
A Closer Look at Internet Protocol
A Closer Look at SS7
The Bearer Plane
Media Gateway Control and Other Softswitch Topics
Session Control
More on SIP and SDP
Implementing Services
Properties of Circuit-Switched Networks
Evolving Toward Carrier-Grade Packet Voice: Recent and Ongoing Developments
Data Link Layer Protocols