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Fax, Modem, and Text for IP Telephony

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  • Description
  • Sample Content
  • Updates
  • Copyright 2008
  • Edition: 1st
  • eBook (Watermarked)
  • ISBN-10: 1-58705-758-1
  • ISBN-13: 978-1-58705-758-8

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

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 StoreandForward 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

            NSF/NSS 499

            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 StoreandForward 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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