Fax, Modem, and Text for IP Telephony
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Fax, Modem, and Text for IP Telephony

5.0 1
by David Hanes, Gonzalo Salgueiro

ISBN-10: 1587052695

ISBN-13: 9781587052699

Pub. Date: 05/02/2008

Publisher: Cisco Press

IP Telephony has revolutionized many aspects of telecommunications and it continues to be deployed at a rapid pace. The benefits of transporting voice over an IP infrastructure include increased flexibility, better scalability, and a significant cost savings over traditional telephony networks. However, during the deployment of these VoIP solutions, other types of


IP Telephony has revolutionized many aspects of telecommunications and it continues to be deployed at a rapid pace. The benefits of transporting voice over an IP infrastructure include increased flexibility, better scalability, and a significant cost savings over traditional telephony networks. However, during the deployment of these VoIP solutions, other types of traditional telephony communications that can also realize these same benefits are often overlooked or ignored.

Fax, Modem, and Text for IP Telephony is a comprehensive resource that confronts the need for information on transporting alternative, non-voice communications over the IP protocol. Beginning with the basic theory and operation of fax, modem, and text telephony, this book then educates you on all of the current transport options that are available. An extensive design guide then provides the pertinent advice and best practices for making the correct planning decisions and choosing the best transport option for your network.

Fax, Modem, and Text for IP Telephony also includes meticulous configuration and troubleshooting guides. The configuration guides in this book include a number of sample configurations and tips to manage any fax, modem, or text deployment. The troubleshooting guides present the essential methodologies, debugs, and analysis tools for quickly resolving both the common and complex issues that may be encountered. This book is the perfect companion to other VoIP resources, and it is the only book that empowers you to successfully handle any fax, modem, or text implementation.

David Hanes, CCIE® No. 3491, is currently a senior engineer specializing in training, network design assistance, and troubleshooting of fax technologies for the Customer Assurance Engineering (CAE) group at Cisco®. Since joining Cisco in 1997, David has worked as a 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.

Gonzalo Salgueiro CCIE No. 4541, is a senior escalation engineer supporting voice, fax, and modem technologies for the Cisco TAC. Gonzalo has spent more than 11 years troubleshooting complex issues in large-scale VoIP networks as well as providing technical leadership for some of the most critical worldwide voice and fax deployments. Prior to joining the Escalation Team in 1999 Gonzalo had roles as a TAC engineer for both the Access/Dial and Multiservice Voice teams as well as a team lead for the Access/Dial team.

  • Learn basic and advanced operational theory and practical implementation of fax, modem, and text communications
  • Understand how to implement fax, modem, and text communications using protocols such as H.323, SIP, MGCP, and SCCP.
  • Explore the functionality and advantages of T.38 fax relay, passthrough, modem relay, T.37 Store-and-Forward Fax, and text relay for IP network deployments
  • Employ expert-recommended best practices and design solutions for deploying fax, modem, and text in an IP telephony environment
  • Optimize your network with comprehensive fax, modem, and text configuration and design tips for use with IOS and non-IOS gateways
  • Master the latest fax, modem, and text troubleshooting tools and techniques employed by Cisco engineers

Category: Cisco Press—IP Communication

Covers: Fax, Modem, and Text Telephony Technologies for Integrated IP Networks

Product Details

Cisco Press
Publication date:
Networking Technology: IP Communications Series
Edition description:
New Edition
Product dimensions:
7.20(w) x 8.90(h) x 1.50(d)

Table of Contents

Introduction xxiii

Part I Laying the Groundwork 3

Chapter 1 How Modems Work 5

A Brief History of Modems 5

Modem Architecture 8

Modem Types 10

External Versus Internal Modems 10

Hardware Versus Software Modems 10

Fax Modems 12

Terminal-to-Modem Communication 14

DTE and DCE 15

RS-232 Signaling 15

Asynchronous Framing 19

User Interface 20

Modem-to-Modem Communication 26

Modulation 26

Frequency Shift Keying (FSK) 28

Phase Shift Keying (PSK) 29

Amplitude Modulation (AM) 30

Quadrature Amplitude Modulation (QAM) 31

Trellis Coded Modulation (TCM) 32

Modulation Standards 33

Modem Call Analysis 34

Call Setup 35

Phase I: Network Interaction 36

Phase II: Probing/Ranging 38

Phase III: Equalizer and Echo Canceller Training 40

Phase IV: Final Training 41

Data Mode 42

Retrains and Speedshifts 42

Error Control 45

Data Compression 48

Call Disconnect 49

Summary 51

Chapter 2 How Fax Works 53

A Brief History of Fax 54

Fax Components 56

Group Classifications 57

Specifications and Standards 58

Fax Modulations 59

Fax Messaging 61

Phases of a Fax Call 62

Message Format Overview 63

Analyzing a Basic Fax Call 65

CNG Tone 66

CED Tone 67

DIS, NSF, and CSI Messages 68

DCS and TSI Messages 71

TCF, CFR, and FTT Messages 73

MPS, EOP, EOM, MCF, RTP, RTN, and DCN Messages 75

Other T.30 Messages 77

Understanding Error Correction Mode 81

ECM Call Analysis 82

PPS and PPR 84

Important G3 Timers 86

Super G3 Faxing 88

Comparison of SG3 and G3 89

Super G3 Call Analysis 89

Page Encoding 91

Modified Huffman 92

Modified READ 97

Modified Modified READ 103

Summary 105

Chapter 3 How Text Telephony Works 107

A Brief History of Text Telephony 107

Text Telephone Terminology 110

Standards and Specifications 110

Carrier Based Versus Carrierless Protocols 111

ITU-T Recommendation V.18 112

Text Telephone Operation 112

Acoustic Coupling Versus Direct Connections 113

Originating and Receiving Text Telephone Calls 114

Conversation Conventions 116

Text Telephone Relay Services 118

HCO (Hearing Carry Over) 119

VCO (Voice Carry Over) 120

Baudot Protocol 121

Baudot Character Set 121

Baudot Modulation Details 123

Summary 124

Part II IP Solutions and Design 127

Chapter 4 Passthrough 129

Passthrough Fundamentals 130

NSE-Based Passthrough 137

Fax Passthrough with NSE 139

Modem Passthrough with NSE 141

Protocol-Based Pass-Through for Fax 143

Fax Pass-Through with H.323 Signaling 144

Fax Pass-Through with SIP Signaling 145

Text over G.711 146

A Future Look at ITU-T V.152 147

Summary 148

Chapter 5 Relay 151

Relay Fundamentals 151

Fax Relay 154

T.38 Fax Relay 155

NSE-Based Switchover for T.38 167

Protocol-Based Switchover for T.38 169

Cisco Fax Relay 173

Modem Relay 175

Cisco Text Relay 181

A Future Look at ITU-T T.38, V.150.1, and V.151 185

Summary 185

Chapter 6 T.37 Store-and-Forward Fax 189

Overview of T.37 Store-and-Forward Fax 189

SMTP Overview 191

SMTP Commands and Sample Sessions 192

DSN and MDN 195

T.37 Onramp 201

T.37 Offramp 203

Summary 204

Chapter 7 Design Guide for Fax, Modem, and Text 207

General Passthrough and Relay Design Considerations 208

Bandwidth 209

Call Control Protocol 214

QoS 215

Redundancy 221

Resource Utilization 224

Secure RTP 227

Timing and Synchronization 229

Fax Design Considerations 231

Gateway Interoperability Considerations 231

Error Correction Mode 233

Super G3 235

Hairpin Calls 237

Fallback 239

T.37 Store-and-Forward Fax 241

Fax Detect Script 243

Unified CM Integration 245

Comparing Fax Passthrough and Fax Relay 249

Modem Design Considerations 251

Comparing Modem Passthrough and Cisco Modem Relay 252

Secure Modem Relay 254

Text Design Considerations 256

Summary and Best Practices 258

Chapter 8 Fax Servers 263

Fax Server Basics 264

Fax Server Integration Solutions 269

Fax Server TDM Integration with a Cisco Voice Gateway 269

Fax Server T.38 Integration with a Cisco Voice Gateway 272

Fax Server T.38 Integration with Unified CM 276

Fax Server Redundancy and Failover 281

Summary 283

Part III Configuration 285

Chapter 9 Configuring Passthrough 287

IOS Gateway Passthrough Configuration 288

IOS Gateway NSE-Based Passthrough Configuration 289

IOS Gateway NSE-Based Passthrough Configuration for H.323, SIP, and SCCP 289

IOS Gateway NSE-Based Passthrough Configuration for MGCP 292

IOS Gateway Protocol-Based Pass-Through Configuration 293

IOS Gateway Text over G.711 Configuration 295

6608 Catalyst Blade Passthrough Configuration 295

VG248 Passthrough Configuration 298

ATA Passthrough Configuration 303

Summary 308

Chapter 10 Configuring Relay 311

IOS Gateway Relay Configuration 311

Fax Relay 312

IOS Gateway Fax Relay Configuration for H.323, SIP, and SCCP 313

IOS Gateway Fax Relay Configuration for MGCP 320

Modem Relay 325

IOS Gateway Cisco Modem Relay Configuration for H.323, SIP, and SCCP 326

IOS Gateway Cisco Modem Relay Configuration for MGCP 329

Cisco Text Relay 332

IOS Example Configurations for Relay 334

Default Fax Relay Configuration for H.323 and SIP 334

Cisco Fax Relay and Modem Passthrough Configuration for H.323 and SIP 336

T.38 Fax Relay, Cisco Modem Relay, and Cisco Text Relay Configuration for H.323‡and‡SIP 337

T.38 Fax Relay and Cisco Text Relay Configuration for SCCP 339

T.38 Fax Relay and Modem Passthrough Configuration for MGCP 340

6608 Catalyst Blade Fax Relay Configuration 342

VG248 Fax Relay Configuration 344

Summary 347

Chapter 11 Configuring T.37 Store and Forward Fax 351

Enabling T.37 Store-and-Forward Fax 351

Loading the TCL Scripts 352

Configuring T.37 Onramp Fax 354

Dial-Peer Configuration for Onramp Fax 355

Fax Receive Configuration Command for Onramp Fax 360

MTA Configuration Commands for Onramp Fax 361

Sample Onramp Configuration 365

Configuring T.37 Offramp Fax 367

Dial-Peer Configuration for Offramp Fax 367

Fax Send Configuration Commands for Offramp Fax 369

MTA Configuration Commands for Offramp Fax 372

Sample Offramp Configuration 373

Summary 375

Part IV Troubleshooting 377

Chapter 12 Troubleshooting Passthrough and Relay 379

Attacking the Problem 380

Fundamental Troubleshooting 382

Checking the Condition of Originating and Terminating Devices 383

Testing with Voice Calls 384

Testing with PSTN Calls 385

Confirming the Configuration 386

Debugging Best Practices 387

Telephony and IP Troubleshooting 391

Call Legs in IOS Gateways 392

Viewing Call Legs 394

Modem Passthrough Call Legs 394

Fax Pass-Through Call Legs 399

Fax Relay Call Legs 400

Cisco Modem Relay Call Legs 402

Text Telephony Call Legs 404

Call Leg Troubleshooting Techniques 405

Telephony Troubleshooting 407

IP Troubleshooting 414

IP Troubleshooting for IOS Gateways 416

IP Troubleshooting for Non-IOS Gateways 419

IP Troubleshooting Using Packet Captures 424

Troubleshooting the Switchover Signaling 428

Troubleshooting NSE-Based Switchovers 430

NSE-Based Switchover for Modem Passthrough 430

NSE-Based Switchover for Cisco Modem Relay 434

NSE-Based Switchover for T.38 Fax Relay 436

Validating NSE Switchover Support 438

Troubleshooting Protocol-Based Switchovers 445

Protocol-Based Fax Pass-Through and T.38 Switchovers for H.323 446

Protocol-Based Fax Pass-Through and T.38 Switchovers for SIP 451

Protocol-Based T.38 Switchover for MGCP 455

Protocol-Based Switchovers and Unified CM 459

Troubleshooting the Cisco Fax Relay Switchover 461

Passthrough and Relay Troubleshooting 464

Troubleshooting DSP Functions 464

DSP HPI Troubleshooting 465

Loss Planning 478

Advanced Troubleshooting for Passthrough 485

Advanced Troubleshooting for Fax Relay 487

Fax Relay Data Rate 487

Dealing with Packet Loss 488

SG3 490

Debugging T.30 Fax Messaging 491

Analyzing T.38 Fax Relay Packet Captures 497


Handling High Delay 500

Advanced Troubleshooting for Modem Relay 503

Checking the Modem Endpoints 503

Debugging Modem Relay 505

Advanced Troubleshooting for Cisco Text Relay 506

PCM Traces for Fax and Modem 510

Capturing PCM Traces 511

Analyzing PCM Traces 515

Summary 523

Chapter 13 Troubleshooting T.37 Store and Forward Fax 525

Checking the Basics 525

T.37 Onramp Troubleshooting 527

Troubleshooting the Onramp Telephony Interface 532

Troubleshooting the TIFF Image Creation 537

Troubleshooting the Onramp SMTP Connection 540

T.37 Offramp Troubleshooting 545

Troubleshooting the Offramp SMTP Connection 549

Troubleshooting the Creation of the Fax Page Image 553

Troubleshooting the Offramp Telephony Interface 556

Summary 559

TOC, 1587052695, 5/20/2008

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5 out of 5 based on 0 ratings. 1 reviews.
Guest More than 1 year ago
This is a great reference book to understand the latest fax, modem and text for IP Telephony technologies. It is certainly not for beginners but more suitable for anyone who has worked with, installed and supported these systems. The prior knowledge of call control protocols, voice gateways, Quality of Services (QoS) and familiarity of Cisco unified voice products and networking is very helpful to understand this book. The book is divided into four parts starting from fundamental theories, solutions and designs, configuration and troubleshooting. It starts with the basic knowledge on how modem, fax and text telephony works. They come with good illustrations and are very easy to understand. Due to space limitation and various standards, the books only addresses the most common and important protocols for each technology. The next part describes various switchover methods and transport options to handle fax, modem and text communication. There are so many technical jargons and complex concepts here that readers who are not familiar with these before, can get lost very fast. The book does a good job describing and comparing each method. The best part of this section is on the design guide chapter which shows reader what design considerations they have to review before implementing fax, modem and text communication for different hardware and network. The configuration part shows various commands and configurations for fax, modem and text for many varieties of Cisco products. I understand that the authors include the configuration parts to complete the reference part of the book. However, since there can be many different commands for different products in different IOS software version, it is best to look up Cisco documentation in the Cisco web site directly rather than using this for configuration basis. The last part describes the troubleshooting techniques and procedures used by Cisco TAC engineers to resolve fax, modem and text problems. This is the best part of the book to get the insight on how ¿divide and conquer¿ troubleshooting is done to find the cause of the problem. It is not easy considering the amount of devices and protocols involved to integrate the fax, modem and text system. I am usually skeptical on any books that try to claim as definitive resources since they usually come short. However, this book is different. The authors successfully manage to incorporate all these technologies and cover them in details. Some readers might think that the delivery is quite dry but it is expected from a resource book. I rate this book 5 out of 5 starts and recommend this book for people who work with the IP Telephony.