IMPLEMENTING VOICE OVER IP Copyright 6 2003 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, e-mail: [email protected]. 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Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data is available. ISBN 0-471-21666-6 Printed in the United States of America 10987654321 IMPLEMENTING VOICE OVER IP BHUMIP KHASNABISH Lexington, Massachusetts, USA A JOHN WILEY & SONS, INC. PUBLICATION This book is dedicated to: Srijesa, Inrava, and Ashmita; My parents, sisters, and brothers; My teachers, present and past Colleagues, and friends; and All of those who consciously and honestly contributed to making me what I am today. CONTENTS Preface xi Acknowledgments xv 1 Background and Introduction 1 The Paradigms, 2 VoIP for Residential Customers, 2 VoIP for Enterprise Customers, 3 Functionally Layered Architectures, 6 Organization of the Book, 12 Epilogue, 14 References, 14 2 Technologies Supporting VoIP 15 Voice Signal Processing, 15 Low-Bit-Rate Voice Signal Encoding, 16 Voice Signal Framing and Packetization, 16 Packet Voice Transmission, 18 Mechanisms and Protocols, 18 Packet Voice Bu¤ering for Delay Jitter Compensation, 25 QoS Enforcement and Impairment Mitigation Techniques, 26 Preventive Mechanisms, 27 Reactive Mechanisms, 27 Future Directions, 29 Epilogue, 30 References, 30 vii viii CONTENTS 3 Evolution of VoIP Signaling Protocols 32 Switch-Based versus Server-Based VoIP, 34 H.225 and H.245 Protocols, 34 Session Initiation Protocol (SIP), 35 MGCP and H.248/Megaco, 39 Stream Control Transmission Protocol (SCTP), 41 Bearer Independent Call Control (BICC), 42 Future Directions, 43 The Promising Protocols, 43 Interworking of PSTN and IP Domain Services, 45 Hybrid Signaling Model, 45 References, 47 4 Criteria for Evaluating VoIP Service 49 Service Requirements Before Call Setup Attempts, 50 Service Requirements During Call Setup Attempts, 50 Service Requirements During a VoIP Session, 51 Voice Coding and Processing Delay, 52 Voice Envelop Delay, 53 Voice Packet Loss, 55 Voice Frame Unpacking and Packet Delay Jitter Bu¤er, 55 Management of Voice Quality During a VoIP Session, 56 Service Requirements After a VoIP Session Is Complete, 57 References, 58 5 A Testbed for Evaluating VoIP Service 59 Description of the Testbed/Network Configuration, 60 PSTN Emulation, 63 IP Network and Emulation of Network Impairments, 64 SS7 Network Emulation and Connectivity, 65 Network Time Server, 65 Telephone Call Emulation Suites, 65 Epilogue, 67 References, 67 6 VoIP Deployment in Enterprises 68 IP-Based Endpoints: Desktop and Conference Phones, 69 IP-PBX, IP Centrex, and IP-Based PBX Tie Lines, 71 IP-VPN and VoIP for Tele-Workers, 77 Web-Based Call and Contact Centers, 79 Next-Generation Enterprise Networks, 81 Customers’ Expectations, 81 Process Reengineering and Consolidation, 83 CONTENTS ix Proactive Maintenance, 83 Support for QoS, 84 Support for Multimedia, 84 Improving Wired Access, 85 Wireless Access, 86 Enterprise Network Management, 88 Epilogue, 88 References, 91 7 VoIP in the Public Networks 93 IP-Based Tandem or CLASS-4 or Long-Distance Services, 93 Elements Required to O¤er VoIP-Based LD Service, 95 A Simple Call Flow, 96 Network Evolution Issues, 98 VoIP in the Access or Local Loop, 99 PSTN Networks, 102 An Architectural Option, 104 An Alternative Architectural Option, 105 CATV Networks, 107 Broadband Wireless Access (Local Loop) Networks, 110 IP-Based Centrex and PBX Services, 111 Epilogue, 113 References, 116 8 VoIP for Global Communications 117 VoIP in Multinational Corporate Networks, 117 VoIP for Consumers’ International Telephone Calls, 122 Epilogue, 125 References, 125 9 Conclusions and Challenges 127 Guidelines for Implementing VoIP, 129 VoIP Implementation Challenges, 132 Simplicity and Ease of Use, 133 Nonstop Service, 133 High-Quality Service, 133 Scalable Solutions, 133 Interoperability, 134 Authentication and Security, 134 Legal and Public Safety–Related Services, 134 Cost-E¤ective Implementation, 135 Epilogue, 135 References, 136 x CONTENTS Appendix A Call Progress Time Measurement in IP Telephony 137 Appendix B Automation of Call Setup in IP Telephony for Tests and Measurements 152 Appendix C Evaluation of VoIP Services 169 Glossary of Acronyms and Terms 178 Index 205 PREFACE In general, voice transmission over the Internet protocol (IP), or VoIP, means transmission of real-time voice signals and associated call control information over an IP-based (public or private) network. The term IP telephony is com- monly used to specify delivery of a superset of the advanced public switched telephone network (PSTN) services using IP phones and IP-based access, transport, and control networks. These networks can be either logically over- layed on the public Internet or connected to the Internet via one or more gate- ways or edge routers with appropriate service protection functions embedded in them. In this book, I use VoIP and IP telephony synonymously, most of the times. This book grew out of my participation in many VoIP-related projects over the past several years. Some of the early projects were exploratory in nature; oscillators had to be used to generate certain tones or signals, and oscilloscopes were used to measure the dial-tone delay, call setup time, and voice transmis- sion delay. However, as the technology matured, a handful of test and mea- surement devices became available. Consequently, we turned out to be better equipped to make more informed decisions regarding the computing and net- working infrastructures that are required to implement the VoIP service. Many of the recent VoIP-related projects in the enterprise and public network indus- tries involve specifying a VoIP service design or upgrading an existing VoIP service platform to satisfy the growth and/or additional feature requirements of the customers. These are living proof of the facts that all-distance voice trans- mission service providers (retailers and wholesalers) and enterprise network designers are seriously deploying or considering the deployment of VoIP ser- vices in their networks. xi xii PREFACE This book discusses various VoIP-related call control, signaling, and trans- mission technologies including architectures, devices, protocols, and service requirements. A testbed and the necessary test scripts to evaluate the VoIP ser- vice and the devices are also included. These provide the essential knowledge and tools required for successful implementation of the VoIP service in both service providers’ networks and enterprise networks. I have organized this information into nine chapters and three appendixes. Chapter 1 provides some background and preliminary information on in- troducing the VoIP service for both residential and enterprise customers. I also discuss the evolution of the monolithic PSTN switching and networking infra- structures to more modular, distributed, and open-interface-based architec- tures. These help rapid rollout of value-added services very quickly and cost- e¤ectively. Chapter 2 reviews the emerging protocols, hardware, and related standards that can be used to implement the VoIP service. These include the bandwidth e‰cient voice coding algorithms, advanced packet queueing, routing, and quality of service delivery mechanisms, intelligent network design and dimen- sioning techniques, and others. No service can be maintained and managed without proper signaling and control information, and VoIP is no exception. The problems become more challenging when one attempts to deliver real-time services over a routed packet-based network. Chapter 3 discusses the VoIP signaling and call control protocols designed to provide PSTN-like call