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Implementing Voice Over IP
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 anyform 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, withouteither the prior written permission of the Publisher, or authorization through payment of theappropriate 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. 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Neither the publisher nor author shall be liable for any loss of profit or any othercommercial damages, including but not limited to special, incidental, consequential, or otherdamages.For general information on our other products and services please contact our Customer CareDepartment within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002.Wiley also publishes its books in a variety of electronic formats. Some content that appears inprint, however, may not be available in electronic format.Library of Congress Cataloging-in-Publication Data is available.ISBN 0-471-21666-6Printed in the United States of America10987654321 IMPLEMENTING VOICEOVER IPBHUMIP KHASNABISHLexington, Massachusetts, USAA JOHN WILEY & SONS, INC. PUBLICATION This book is dedicated to:Srijesa, Inrava, and Ashmita;My parents, sisters, and brothers;My teachers, present and pastColleagues, and friends; andAll of those who consciously andhonestly contributed tomaking me what I am today. CONTENTSPreface xiAcknowledgments xv1 Background and Introduction 1The Paradigms, 2VoIP for Residential Customers, 2VoIP for Enterprise Customers, 3Functionally Layered Architectures, 6Organization of the Book, 12Epilogue, 14References, 142 Technologies Supporting VoIP 15Voice Signal Processing, 15Low-Bit-Rate Voice Signal Encoding, 16Voice Signal Framing and Packetization, 16Packet Voice Transmission, 18Mechanisms and Protocols, 18Packet Voice Bu¤ering for Delay Jitter Compensation, 25QoS Enforcement and Impairment Mitigation Techniques, 26Preventive Mechanisms, 27Reactive Mechanisms, 27Future Directions, 29Epilogue, 30References, 30vii 3 Evolution of VoIP Signaling Protocols 32Switch-Based versus Server-Based VoIP, 34H.225 and H.245 Protocols, 34Session Initiation Protocol (SIP), 35MGCP and H.248/Megaco, 39Stream Control Transmission Protocol (SCTP), 41Bearer Independent Call Control (BICC), 42Future Directions, 43The Promising Protocols, 43Interworking of PSTN and IP Domain Services, 45Hybrid Signaling Model, 45References, 474 Criteria for Evaluating VoIP Service 49Service Requirements Before Call Setup Attempts, 50Service Requirements During Call Setup Attempts, 50Service Requirements During a VoIP Session, 51Voice Coding and Processing Delay, 52Voice Envelop Delay, 53Voice Packet Loss, 55Voice Frame Unpacking and Packet Delay Jitter Bu¤er, 55Management of Voice Quality During a VoIP Session, 56Service Requirements After a VoIP Session Is Complete, 57References, 585 A Testbed for Evaluating VoIP Service 59Description of the Testbed/Network Configuration, 60PSTN Emulation, 63IP Network and Emulation of Network Impairments, 64SS7 Network Emulation and Connectivity, 65Network Time Server, 65Telephone Call Emulation Suites, 65Epilogue, 67References, 676 VoIP Deployment in Enterprises 68IP-Based Endpoints: Desktop and Conference Phones, 69IP-PBX, IP Centrex, and IP-Based PBX Tie Lines, 71IP-VPN and VoIP for Tele-Workers, 77Web-Based Call and Contact Centers, 79Next-Generation Enterprise Networks, 81Customers’ Expectations, 81Process Reengineering and Consolidation, 83viiiCONTENTS Proactive Maintenance, 83Support for QoS, 84Support for Multimedia, 84Improving Wired Access, 85Wireless Access, 86Enterprise Network Management, 88Epilogue, 88References, 917 VoIP in the Public Networks 93IP-Based Tandem or CLASS-4 or Long-Distance Services, 93Elements Required to O¤er VoIP-Based LD Service, 95A Simple Call Flow, 96Network Evolution Issues, 98VoIP in the Access or Local Loop, 99PSTN Networks, 102An Architectural Option, 104An Alternative Architectural Option, 105CATV Networks, 107Broadband Wireless Access (Local Loop) Networks, 110IP-Based Centrex and PBX Services, 111Epilogue, 113References, 1168 VoIP for Global Communications 117VoIP in Multinational Corporate Networks, 117VoIP for Consumers’ International Telephone Calls, 122Epilogue, 125References, 1259 Conclusions and Challenges 127Guidelines for Implementing VoIP, 129VoIP Implementation Challenges, 132Simplicity and Ease of Use, 133Nonstop Service, 133High-Quality Service, 133Scalable Solutions, 133Interoperability, 134Authentication and Security, 134Legal and Public Safety–Related Services, 134Cost-E¤ective Implementation, 135Epilogue, 135References, 136CONTENTSix [...]... VoIP Session, 51 Voice Coding and Processing Delay, 52 Voice Envelop Delay, 53 Voice Packet Loss, 55 Voice Frame Unpacking and Packet Delay Jitter BuÔer, 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. .. me xv 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,... interconnected by an IP network. Here the network access from the terminal device (e.g., a black phone) can still be provided by a traditional CLASS-5 switch, but the inter-LATA transmission of a voice signal is oÔered over an IP network. The resulting architecture demands VoIP GWs to convert the TDM-formatted voice signal into IP packets at the ingress and vice versa at the egress. The VoIP GK controls... generates a 64 Kbps voice stream. G.723 uses (CELP) technique to produce a 5.3 Kbps voice stream, and G.723.1 uses (MP-MLQ) technique to produce a 6.4 Kbps voice stream. Both G.729 and G.729A use (CS-ACELP) technique to produce an 8 Kbps voice stream. Usually a 5 to 48 msec voice frame sample is encoded, and sometimes mul- tiple voice frames are packed into one packet before encapsulating voice signal in... of the voice signal, which commonly results in degrada- tion of voice quality. Additional hardware-based echo-canceller and higher- speed transmission mechanisms are generally required to improve voice quality in such scenarios. As shown in Figure 2-2, IP- based transmission of a digitized voice signal for (real-time) telephony service requires the addition of multiple levels of encapsulation overheads.... Delivering Voice over Frame Relay and ATM, John Wiley & Sons, New York, 1998. 5. G.764 Recommendation, Voice Packetization—Packetized Voice Protocols, ITU-T, Geneva, 1990. 30 TECHNOLOGIES SUPPORTING VoIP ACKNOWLEDGMENTS My hat goes oÔ to my children who inspired me to write this book. They naively interpreted the VoIP network elements as the legos during their visits with me to many of the VoIP Labs.... 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,... both IP and various types of DSL tech- nologies for integrated voice, data, and video communications is shown in Figure 1-5 [6]. For very large corporations with nationwide branch o‰ces and for multi- national corporations with international o‰ces, VoIP implementation may be preferable because such corporations may already have a large operational IP or overlay -IP network in place. The addition of VoIP... and budgetary constrains. VoIP FOR RESIDENTIAL CUSTOMERS In the traditional PSTN networks, the network elements and their intercon- nections are usually organized into five hierarchical layers [3] or tiers, as shown 3 VoIP GW translates time division multiplex (TDM) formatted voice signals into a real-time transport protocol (RTP) over a user datagram protocol (UDP) over IP packets. 4 The GK controls... of voice quality is usually more sensi- tive to packet loss and delay jitter than to packet transmission delay. Some information on various voice coding schemes and quality degradation because Figure 2-2 Encapsulation of a voice frame for transmission over the Internet. PACKET VOICE TRANSMISSION 19 For survivability, all of these protocols must interwork gracefully with H.323- and/or SIP-based VoIP . VoIP Deployment in Enterprises 6 8IP- Based Endpoints: Desktop and Conference Phones, 6 9IP- PBX, IP Centrex, and IP- Based PBX Tie Lines, 7 1IP- VPN and VoIP. general, voice transmission over the Internet protocol (IP) , or VoIP, meanstransmission of real-time voice signals and associated call control informationover