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Bruce Hartpence
Packet Guide to Voice over IP
www.it-ebooks.info
Packet Guide to Voice over IP
by Bruce Hartpence
Copyright © 2013 Bruce Hartpence. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
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February 2013:
First Edition
Revision History for the First Edition:
2013-02-21: First release
See http://oreilly.com/catalog/errata.csp?isbn=9781449339678 for release details.
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responsibility for errors or omissions, or for damages resulting from the use of the information contained
herein.
ISBN: 978-1-449-33967-8
[LSI]
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Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
1.
Introduction to Voice over the Internet Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What Is VoIP? 2
Real-time Versus Nonreal-time Data 5
Why Change to VoIP? 7
The Business Case 8
VoIP and FCC Regulation 9
911 10
A Note on Power 11
General VoIP Topologies 11
Power over Ethernet 15
PoE Basic Operation 16
VoIP Protocols 17
Signaling Protocols 18
Transport Protocol 20
VoIP Basic Operation 21
Performance 29
Unified Communications 30
Summary 31
Standards and Reading 31
Review Questions 32
Review Question Answers 32
Lab Activities 33
Activity 1—Review of the Standards 33
Activity 2—Download Wireshark and the Capture Files for This Chapter 33
Activity 3—Examine VoIP Offerings in Your Area 33
Activity 4—Take a Look at the FCC Website 34
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Activity 5—Latency, Packet Loss, and Jitter 34
2. Traditional Telephony. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Introduction 35
Overview 37
Organizations 38
Connecting to the Traditional World 40
Telecommunication Companies 42
Telephone Wiring 47
Data Cabling, EIA568 A and B 48
POTS and the Local Loop 50
T-1 53
Integrated Services Digital Network 55
Basic Telephone-Call Operation 56
Summary 58
Standards and Reading 59
Review Questions 59
Review Question Answers 60
Lab Activities 60
Activity 1—Review Your Local Telephone Connections 60
Activity 2—Experiment with the Desktop Telephone or VoIP Phone 61
Activity 3—Wiring to the PBX or Central Office 61
Activity 4—ITU-T Recommendations 61
3.
Session Initiation Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Introduction 63
Protocol Description 64
Components 64
Addressing 66
Basic Operation 67
SIP Messages and Message Structure 71
Requests 72
Responses 72
Header Fields 73
Basic Operation Continued 76
Session Description Protocol (SDP) 76
Trunks 87
Security 88
Summary 90
Standards and Reading 90
Review Questions 91
Review Question Answers 91
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Lab Activities 92
Activity 1—Build the Topology Shown 92
Activity 2—Packet Capture 93
Activity 3—Packet Capture Analysis 93
Activity 4—Phone-Call Analysis 93
Activity 5—SDP 94
4.
The Real-Time Transport Protocol and the Real-Time Control Protocol. . . . . . . . . . . . . . 95
Protocol Description 96
Profiles 97
Basic Operation 97
Protocol Structure 99
RTP Control Protocol 108
Detailed Operation 112
Security 113
Vectors 113
SRTP Operation 114
Summary 116
Standards and Reading 117
Review Questions 117
Review Answers 118
Lab Activities 118
Activity 1—Topology Build 118
Activity 2—Analysis of the RTP Stream 119
Activity 3—The Codec 120
Activity 4—Analysis of the RTCP Stream 120
5.
Codecs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Audio Frequencies 121
Voice Signals 122
Audio Coders and Decoders 124
Sampling 125
Quantizing 125
ITU-T G Series Specifications 128
Codec Selection and Performance 130
Transcoding 132
Packet Loss and Packet Loss Concealment (PLC) 134
What Codec Are You Using? 135
Video Signals 135
Sending a Series of Pictures 137
Video Encoding 138
Standards Groups for Video 140
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Profiles 141
ITU-T Video Recommendations 141
ISO/IEC Video Standards 144
Summary 144
Standards and Reading 145
Review Questions 145
Review Question Answers 146
Lab Activities 146
Activity 1—Colors 146
Activity 2—File Sizes 147
Activity 3—Audio Quality 148
Activity 4—Video Quality 148
6. H.323 ITU-T Recommendation for Packet-Based Multimedia Communications Systems 151
Recommendation Description 153
Subprotocols 155
Basic Operation and Message Structure 156
H.225 Messaging 158
Q.931 Fields 159
H.225 Message Format 161
H.225 RAS 163
H.225 Standard Messages 170
H.225 Modes 173
Other H.225 Messages 175
H.245 177
Voice Data 182
Termination 183
Summary 185
Standards and Reading 185
Review Questions 186
Review Question Answers 186
Lab Activities 187
Activity 1—Build the Topology Shown 187
Activity 2—Capture Setup 188
Activity 3—Packet Capture Analysis 188
Activity 4—Phone-Call Analysis 188
Activity 5—H.245 189
7.
Skinny Client Control Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Protocol Description 192
Structure 192
Basic Header Format 192
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Topology Construction 193
Operational Stages 196
Startup 197
Registration 197
Picking up the Handset—Going Off-Hook 202
Dialing a Number 203
At the Receiver 205
Back at the Source Phone 208
Voice Data 209
Teardown of the Call 210
Performance Measuring 211
Off-Site Calling 215
Summary 218
Reading 218
Review Questions 220
Review Answers 220
Lab Activities 221
Activity 1—Basic Topology Build 221
Activity 2—Going Off-Hook 222
Activity 3—Show and Debug 222
Activity 4—Call-Flow Diagram 223
Activity 5—Multiple Call Managers 223
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[...]... protocol Adopting late might put you behind the competition or make you rush to deploy a system that is not well understood by the local staff Voice over the Internet Protocol, a.k.a Voice over IP, or VoIP, is a huge topic Those trying to really understand how VoIP systems operate and the issues associated with their deployment must delve into protocols and architecture requirements such as power over. .. developers do not want to concern themselves with lost or delayed packets Performance of the application might suffer if they did The packet in Figure 1-5 also happens to encapsulate a Real-Time Transport Protocol (RTP) message RTP is used by VoIP deployments to transfer voice and video data Figure 1-5 UDP packet Why Change to VoIP? With all of this disruption, why would we switch to Voice over IP? Probably... protocols and architectures used by VoIP-based systems as we track connections from the time VoIP phones boot, through calls and during subsequent connection tear‐ down Like the previous Packet Guide books (O’Reilly’s Packet Guide to Core Network Protocols and the Packet Guide to Routing and Switching), the tool of choice for viewing ix www.it-ebooks.info the packets will be Wireshark, which is still... common web protocols such as the Hypertext Transfer Protocol, making it easy to understand and read Chapter 4, The Real-Time Transport Protocol and the Real-Time Control Protocol VoIP protocols are broken into two categories: signaling and transport The RealTime Transport Protocol (RTP) and its sidekick, the Real-Time Control Protocol (RTCP), fall into the latter category Almost every voice or video... trying to understand telecom—may you meet in the middle xiv | Preface www.it-ebooks.info CHAPTER 1 Introduction to Voice over the Internet Protocol Enter the expansion of Voice over IP with its disruptive transition of voice from the old circuit switched networks to new IP- based networks —Mark Spencer in the foreword for Asterisk: The Future of Telephony Several years ago, most of the writing about Voice. .. Introduction to Voice over the Internet Protocol This chapter provides the foundation for the book It includes the requirements for a basic VoIP topology and describes the issues associated with deploying packetized voice and video Readers will also come to understand critical topics such as codecs and power over Ethernet Chapter 2, Traditional Telephony Every data network must eventually connect to the... had to compete with whatever was running on the computer at the time Today, we have a mix of desktop VoIP phones and telephony applications, or softphones 14 | Chapter 1: Introduction to Voice over the Internet Protocol www.it-ebooks.info Non-VoIP components The VoIP system depends on a number of services that are not VoIP specific Many of the services, such as the Dynamic Host Configuration Protocol... signaling or potential problems can lead to quick problem resolution VoIP Protocols As mentioned earlier, there are several VoIP-specific protocols but only two categories: signaling and transport The signaling protocols handle the functions derived from the telephone system architecture, and the transport protocols carry the voice packets gen‐ erated from the codec Phones use the signaling protocol to register... Session Initiation Protocol, or SIP Session Initiation Protocol The Session Initiation Protocol (SIP) is a nonproprietary standard from the Internet Engineering Task Force, or IETF The format of SIP messages is very close to that of Hypertext Transfer Protocol (HTTP) packets and so is very familiar to folks in the data networking world SIP had a slow start but has largely taken over the world Though... Employees using the VoIP endpoints may experience greater mobility if wireless phones are supported, but softphones and the ability to log into any phone may also increase mobility and productivity Pundits often point to these advantages as well as integration with other applications as nonfinancial reasons to switch to VoIP 8 | Chapter 1: Introduction to Voice over the Internet Protocol www.it-ebooks.info . www.it-ebooks.info
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Bruce Hartpence
Packet Guide to Voice over IP
www.it-ebooks.info
Packet Guide to Voice over IP
by Bruce Hartpence
Copyright © 2013. Like the previous Packet Guide books (O’Reilly’s Packet Guide to Core Network
Protocols and the Packet Guide to Routing and Switching), the tool of choice
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