Dsl and Adsl Modems
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Contents
Introduction
The Fundamental Problem of Communications
The Transmission Medium-Attenuation Constraints
The Transmission Medium- Interference Constraints
The Transmission Medium- Bandwidth Constraints
DSL Keeps Unshielded Twisted Pair (UTP) Copper Cable
Attractive as a Premises Transmission Medium
A Brief History of DSL
Program
xDSL Modems: Fundamentals and Flavors
The Simple DSL Transceiver
The Many Flavors of DSL
2.2.1
2.2.2
The HDSL Family: HDSL, SDSL, MSDSL and HDSL2
2.2.3
The ADSL Family: ADSL, MDSL, RADSL and
Splitterless DSL
2.2.4
The Role of DSLAMsers
Virtual DSL: The Role of the DSL Simulator
Standards
Digital Subscriber Line – DSL Glossary
Bibliography
Index of Illustrations
Figure 1-1
Source, User pair with information
Figure 1-2
Representations of information
Figure 1-3
Examples of sources and users generating/desiring “data”
Figure 1-4
Source, transmission medium, user
Figure 1-5
Disturbance travelling in transmission medium
Figure 1-6
The model which represents the fundamental problem of
Communications
Figure 1-7
Input data signal attenuating as it propagates down a
transmission medium
Figure 1-8
Regenerating and repeating an attenuated signal in order to
reach user
Figure 1-9
Example transfer function of a transmission medium
Figure 1-10
Binary data from source represented by impulse train put into
transmission medium by transmitter. Impulses are T seconds apart
Figure 1-11
Input signal is positive impulse. Resulting output signal shows
time dispersion
Figure 1-12
Cost trends of common transmission media
Figure 2-1
A typical DSL Transceiver block diagram
Figure 2-2
Transmitter of digital transmission system
Figure 2-3
Generic DSL Reference Model
Figure 2-4
T1 Components
Figure 2-5
The HDSL Architecture
Figure 2-6
Photo of Model 681/682 HDSL Modem
Figure 2-7
ADSL reference model
Figure 2-8
Conventional ADSL configuration with splitter
Figure 2-9
Photo of Model 684 MDSL Modem
Figure 2-10
The VDSL Architecture
Figure 3-1
DSL-based services reference diagram
Figure 4-1
Diagram of modem testing on local loop connection
Figure 4-2
Diagram of modem testing on coil of twisted pair cable
Figure 4-3
Diagram of modem testing on DSL Simulator
Figure 4-4
Photo of Model 454 – Local Loop Simulator
Figure 4-5
Photo of Model 455 – Local Loop Simulator
Figure 4-6
Photo of Model 457 – Automated Local Loop Simulator
Figure 4-7
Photo of Model 456 – Loop Interference Simulator
Figure 4-8
Diagram of Models 454 and 456
Introduction
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