Dsl and Adsl Modems

Contents

1. Introduction

1.1 The Fundamental Problem of Communications 5

1.2 The Transmission Medium-Attenuation Constraints 9

1.3 The Transmission Medium- Interference Constraints 12

1.4 The Transmission Medium- Bandwidth Constraints 13

1.5 DSL Keeps Unshielded Twisted Pair (UTP) Copper Cable

Attractive as a Premises Transmission Medium 18

1.6 A Brief History of DSL 21

1.7 Program 22

2. xDSL Modems: Fundamentals and Flavors

2.1 The Simple DSL Transceiver 24

2.2 The Many Flavors of DSL 28

2.2.1 IDSL 28

2.2.2 The HDSL Family: HDSL, SDSL, MSDSL and HDSL2 28

2.2.3 The ADSL Family: ADSL, MDSL, RADSL and

Splitterless DSL 33

2.2.4 VDSL 36

3. The Role of DSLAMsers 37

4. Virtual DSL: The Role of the DSL Simulator 39

5. Standards 46

6. Digital Subscriber Line - DSL Glossary 48

Bibliography 95

Index of Illustrations

Figure 1-1 Source, User pair with information 5

Figure 1-2 Representations of information 6

Figure 1-3 Examples of sources and users generating/desiring "data" 6

Figure 1-4 Source, transmission medium, user 7

Figure 1-5 Disturbance travelling in transmission medium 7

Figure 1-6 The model which represents the fundamental problem of

Communications 8

Figure 1-7 Input data signal attenuating as it propagates down a

transmission medium 10

Figure 1-8 Regenerating and repeating an attenuated signal in order to

reach user 11

Figure 1-9 Example transfer function of a transmission medium 14

Figure 1-10 Binary data from source represented by impulse train put into

transmission medium by transmitter. Impulses are T seconds apart 15

Figure 1-11 Input signal is positive impulse. Resulting output signal shows

time dispersion 16

Figure 1-12 Cost trends of common transmission media 19

Figure 2-1 A typical DSL Transceiver block diagram 25

Figure 2-2 Transmitter of digital transmission system 26

Figure 2-3 Generic DSL Reference Model 27

Figure 2-4 T1 Components 29

Figure 2-5 The HDSL Architecture 30

Figure 2-6 Photo of Model 681/682 HDSL Modem 31

Figure 2-7 ADSL reference model 34

Figure 2-8 Conventional ADSL configuration with splitter 34

Figure 2-9 Photo of Model 684 MDSL Modem 35

Figure 2-10 The VDSL Architecture 37

Figure 3-1 DSL-based services reference diagram 39

Figure 4-1 Diagram of modem testing on local loop connection 41

Figure 4-2 Diagram of modem testing on coil of twisted pair cable 41

Figure 4-3 Diagram of modem testing on DSL Simulator 42

Figure 4-4 Photo of Model 454 - Local Loop Simulator 43

Figure 4-5 Photo of Model 455 - Local Loop Simulator 43

Figure 4-6 Photo of Model 457 - Automated Local Loop Simulator 44

Figure 4-7 Photo of Model 456 - Loop Interference Simulator 45

Figure 4-8 Diagram of Models 454 and 456 45

1. Introduction

1.1 The Fundamental Problem of Communications

The subject of interest in this book is the use of Digital Subscriber Line (DSL) technology to increase the rate and improve the quality of data communications over copper cable. It is an important topic both within the context of data communications today and into the future. All, or almost all, aspects of this subject will be explored. However, it seems rather forbidding just to jump into this topic. Rather, it is more appropriate to take a step back and talk about the nature of communications first, in order to introduce some needed terminology. Such a step back will also provide us with a broader perspective on the subject of DSL technology as a transmission facilitator. In short, it will help us to answer the question, "Why should we be interested in DSL?"

The reader well-versed in data communications may, of course, choose to skip this introduction and suffer no real penalty.

The subject of communications really begins with the situation shown in Figure 1-1. Here is an entity called the Source and one called the User - located remotely from the Source. The Source generates Information, and the User desires to learn what this Information is.

Figure 1-1: Source, User pair with information

Examples of this situation abound. However, let us focus our attention on the case illustrated in Figure 1-2. Here, the Information is a sequence of binary digits - 0s and 1s, commonly called "bits." Information in this case is termed "data." Information of this type is generally associated with computers, computing-type devices, and peripherals

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