Fax, Modem, and Text for Ip Telephony

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  • Edition: 1st
  • Format: Paperback
  • Copyright: 2008-06-11
  • Publisher: Cisco Press
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Master the basics of modems, fax, and text telephony technologies, including how modems and faxes work in an IP network infrastructure.

Author Biography

David Hanes, CCIE No. 3491, currently works as an engineer for the Cisco Customer Assurance Engineering (CAE) group based out of Research Triangle Park, North Carolina supporting various emerging technologies through product testing and field trials. In addition, David is a technical expert for Cisco in the area of fax over IP technologies and assists with network design and troubleshooting for critical fax over IP deployments. Since joining Cisco in 1997, he has worked as a Technical Assistance Center (TAC) engineer for the WAN, WAN Switching, and Multiservice Voice teams, a team lead for the Multiservice Voice team, and an Escalation Engineer covering a variety of voice and fax technologies. David has troubleshot escalated issues in Cisco customer networks worldwide and remains a technical resource for other Cisco employees and customers. Before working at Cisco, David was a Systems Engineer for Sprint, where he gained his first computer networking experience working on the Frame Relay and X.25 protocols. He holds a bachelor of science degree in electrical engineering from North Carolina State University.


Gonzalo Salgueiro, CCIE No. 4541, is a senior engineer for the Unified Communications Infrastructure Escalation team of the Technical Assistance Center (TAC) in Research Triangle Park, North Carolina. In his current role, he is a technical leader for fax and voice over IP technologies working directly with Cisco development engineering, TAC support teams, and product serviceability organization, providing support for various Unified Communications products and technologies. Over the past 12 years at Cisco, he has specialized in troubleshooting complex issues for some of the largest VoIP networks and has provided technical leadership for some of the most critical worldwide voice and fax deployments. Before joining the Escalation team in 1999, Gonzalo had roles as a TAC engineer for both the Access/Dial and Multiservice Voice teams and as a team lead for the Access/Dial team. Gonzalo has developed and delivered all levels of training and documentation on these technologies both internally to Cisco technical teams and externally to Cisco customers worldwide. He holds a bachelor of science degree in physics from Jacksonville University and a master of science degree in physics from the University of Miami.


Table of Contents

Introductionp. xxiii
Laying the Groundworkp. 3
How Modems Workp. 5
A Brief History of Modemsp. 5
Modem Architecturep. 8
Modem Typesp. 10
External Versus Internal Modemsp. 10
Hardware Versus Software Modemsp. 10
Fax Modemsp. 12
Terminal-to-Modem Communicationp. 14
DTE and DCEp. 15
RS-232 Signalingp. 15
Asynchronous Framingp. 19
User Interfacep. 20
Modem-to-Modem Communicationp. 26
Modulationp. 26
Frequency Shift Keying (FSK)p. 28
Phase Shift Keying (PSK)p. 29
Amplitude Modulation (AM)p. 30
Quadrature Amplitude Modulation (QAM)p. 31
Trellis Coded Modulation (TCM)p. 32
Modulation Standardsp. 33
Modem Call Analysisp. 34
Call Setupp. 35
Network Interactionp. 36
Probing/Rangingp. 38
Equalizer and Echo Canceller Trainingp. 40
Final Trainingp. 41
Data Modep. 42
Retrains and Speedshiftsp. 42
Error Controlp. 45
Data Compressionp. 48
Call Disconnectp. 49
Summaryp. 51
How Fax Worksp. 53
A Brief History of Faxp. 54
Fax Componentsp. 56
Group Classificationsp. 57
Specifications and Standardsp. 58
Fax Modulationsp. 59
Fax Messagingp. 61
Phases of a Fax Callp. 62
Message Format Overviewp. 63
Analyzing a Basic Fax Callp. 65
CNG Tonep. 66
CED Tonep. 67
DIS, NSF, and CSI Messagesp. 68
DCS and TSI Messagesp. 71
TCF, CFR, and FTT Messagesp. 73
MPS, EOP, EOM, MCF, RTP, RTN, and DCN Messagesp. 75
Other T.30 Messagesp. 77
Understanding Error Correction Modep. 81
ECM Call Analysisp. 82
PPS and PPRp. 84
Important G3 Timersp. 86
Super G3 Faxingp. 88
Comparison of SG3 and G3p. 89
Super G3 Call Analysisp. 89
Page Encodingp. 91
Modified Huffmanp. 92
Modified READp. 97
Modified Modified READp. 103
Summaryp. 105
How Text Telephony Worksp. 107
A Brief History of Text Telephonyp. 107
Text Telephone Terminologyp. 110
Standards and Specificationsp. 110
Carrier Based Versus Carrierless Protocolsp. 111
ITU-T Recommendation V.18p. 112
Text Telephone Operationp. 112
Acoustic Coupling Versus Direct Connectionsp. 113
Originating and Receiving Text Telephone Callsp. 114
Conversation Conventionsp. 116
Text Telephone Relay Servicesp. 118
HCO (Hearing Carry Over)p. 119
VCO (Voice Carry Over)p. 120
Baudot Protocolp. 121
Baudot Character Setp. 121
Baudot Modulation Detailsp. 123
Summaryp. 124
IP Solutions and Designp. 127
Passthroughp. 129
Passthrough Fundamentalsp. 130
NSE-Based Passthroughp. 137
Fax Passthrough with NSEp. 139
Modem Passthrough with NSEp. 141
Protocol-Based Pass-Through for Faxp. 143
Fax Pass-Through with H.323 Signalingp. 144
Fax Pass-Through with SIP Signalingp. 145
Text over G.711p. 146
A Future Look at ITU-T V.152p. 147
Summaryp. 148
Relayp. 151
Relay Fundamentalsp. 151
Fax Relayp. 154
T.38 Fax Relayp. 155
NSE-Based Switchover for T.38p. 167
Protocol-Based Switchover for T.38p. 169
Cisco Fax Relayp. 173
Modem Relayp. 175
Cisco Text Relayp. 181
A Future Look at ITU-T T.38, V.150.1, and V.151p. 185
Summaryp. 185
T.37 Store-and-Forward Faxp. 189
Overview of T.37 Store-and-Forward Faxp. 189
SMTP Overviewp. 191
SMTP Commands and Sample Sessionsp. 192
DSN and MDNp. 195
T.37 Onrampp. 201
T.37 Offrampp. 203
Summaryp. 204
Design Guide for Fax, Modem, and Textp. 207
General Passthrough and Relay Design Considerationsp. 208
Bandwidthp. 209
Call Control Protocolp. 214
QoSp. 215
Redundancyp. 221
Resource Utilizationp. 224
Table of Contents provided by Publisher. All Rights Reserved.


Introduction IntroductionThe advent of VoIP has led to revolutionary changes in the world of telecommunications. Information that was transported on traditional telephony infrastructures such as voice, video, and modulated data is transitioning to IP backbones. However, in this transition process, modulated data such as fax, modem, and text is often overlooked. Fax, modem, and text are treated like regular voice communications in many cases when in fact they have different transport requirements and usually need unique transport protocols for communication to be reliable.We, the authors of this book, have about 25 years of combined networking experience with the majority of it focusing on faxes, modems, and VoIP. We have seen and experienced firsthand as Cisco TAC engineers the problems that are encountered with fax and modem communications. While one of the most common problems we encounter is the failure to take into account the unique transport requirements of fax, modem, and text, we also have seen problems with the configuration of the multitude of fax-, modem-, and text-related commands in Cisco voice gateways. In addition, we have realized that many times there is just a lack in understanding of basic passthrough and relay fundamentals as they are implemented on Cisco voice products. Addressing these problems and how to troubleshoot them were our main focus while writing this book.Therefore, you will notice that this book includes a comprehensive design guide for getting fax, modem, and text deployments working successfully from the start, a commonsense configuration section, and a thorough troubleshooting guide. Equally as important, we devoted a whole section to the fundamentals of passthrough and relay and how they are implemented on Cisco voice products. In this book, we address all the main difficulties that we have seen with the implementation of fax and modems in IP environments.We have written this book to be the definitive resource for understanding, designing, configuring, and troubleshooting fax, modem, and text in today's IP networks. Whether you are a network designer, voice engineer, or simply someone who must support fax, modem, and text communications over IP networks, this book is practically a necessity. If you understand basic VoIP, this book will just build upon that core knowledge.Many books and other resources are available that discuss VoIP, and some even have a casual mention of transporting fax or modem communications. However, this book is the only one that provides a comprehensive, one-stop reference for addressing all aspects of fax, modem, and text communication. Target Release: Cisco IOS Software Version 12.4(9)T1The examples and features explained throughout this book for Cisco IOS voice gateways target Cisco IOS Software Release 12.4(9)T1. However, other IOS versions should be applicable to the majority of this book, too. Be aware, however, that features and implementations might differ somewhat in other IOS versions. Other software versions for devices such as Cisco Unified Communications Manager, 6608, and the VG248 are noted in the text when applicable. Goals and MethodsThis book is designed to be the only resource you will ever need for handling fax, modem, and text communications in IP telephony environments. From basic theory to design solutions to configuration to troubleshooting, all aspects are covered in a clear, concise manner. Who Should Read This Book?Just about every IP telephony (IPT) installation has at least one fax machine, and larger installations often include modems and text telephony devices, too. If you work with IPT, your job has already required or more than likely will require in the future that you handle fax, modem, and text communications in your network. For this reason, this book is an indispensable resource that shoul

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