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ECS5365 Invited Lecture Overview of Digital Subscriber Line. James Kershaw Transmission Systems Division NEC Australia Pty Ltd http://www.nec.com.au. Agenda. What is Digital Subscriber Line? Standardization DSL Architecture Technical Issues Typical Applications. Digital Subscriber Line.

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Ecs5365 invited lecture overview of digital subscriber line

ECS5365 Invited LectureOverview of Digital Subscriber Line

James Kershaw

Transmission Systems Division

NEC Australia Pty Ltd

http://www.nec.com.au


Agenda
Agenda

  • What is Digital Subscriber Line?

  • Standardization

  • DSL Architecture

  • Technical Issues

  • Typical Applications


Digital subscriber line
Digital Subscriber Line

  • Modem based Access Technology

  • Existing Subscriber Infrastructure

  • Higher Speed Connections

  • Pair Gain Capability


Advantages of dsl
Advantages of DSL

  • Point to Point Connection

    • Dedicated bandwidth

    • Inherent Security

  • Existing Infrastructure

    • Reduced roll-out costs

  • Cheaper Operating Costs


Types of dsl

ISDN

IDSL - ISDN DSL

MDSL - Multi-rate DSL

SDSL - Single-loop DSL

HDSL - High-speed DSL

SHDSL - Single Pair HDSL

RADSL - Rate Adaptive ADSL

ADSL - Asymmetric DSL

VDSL -Very-high-speed DSL

Performance

Types of DSL


Standardization
Standardization

  • What needs to be standardized?

  • Who is involved with Standardization?

  • What standards exist?


What needs to be standardized
What needs to be standardized?

  • Physical Interfaces

  • Electrical Interfaces

  • Link Layer Behaviour

  • Network Layer Behaviour

  • Signaling and Negotiation

  • Test Procedures

  • Electrical Compatibility


Who is involved
Who is Involved

  • National Bodies eg. ANSI

  • Regional Bodies eg. ETSI

  • International Bodies eg, ITU-T, IETF

  • Special Interest Groups eg. ADSLF, ATMF


International dsl standards
International DSL Standards

  • ITU-T Standards

    • G.991 (G.hdsl) - T1/E1 symmetric

    • G.991.2 (G.shdsl) - under study

    • G.992.1(G.dmt) - 16 Mbit/s down, 1.1 Kbit/s up

      • Annex A - ADSL over POTS

      • Annex B - ADSL over ISDN

      • Annex C - ADSL over POTS, suitable for Japan

    • G.992.2 (G.lite) - 1500/640Kbit/s

    • G.993 (G.vdsl) - under study

    • G.994.1 (G.handshake) - DSL Negotiation


National regional standards
National/Regional Standards

  • American National Standards Institute

    • eg T1.413  G.992.1, TR 28 = HDSL

  • European Telecommunications Standardization Institute

    • eg ETR 328  ADSL, TS101 135  TR 28


Special interest groups
Special Interest Groups

  • ADSL Forum

    • System Architecture and Interoperability

    • Creates Technical Reports

  • ATM Forum

    • ADSL is yet another physical layer for ATM

    • Creates Industry Specifications

  • Others


Dsl architecture
DSL Architecture

  • Reference Architecture

  • Medium

  • Modulation

  • Spectrum

  • Typical Configurations


Reference architecture adslf

V

U

T

S

Regional

Broadband

Network

Customer

Premises

Network

Customer

Premises

Equipment

Service

Provider

Access

Node

Network

Termination (B-NT)

Core Network

A11

A10

Reference Architecture (ADSLF)

A11, A10 are from DAVIC

V,U,T, S are from ITU-T


Dsl medium
DSL Medium

  • Twisted Pair

    • Two Wire

      • ADSL, IDSL, SDSL, HDSL2, VDSL

    • Four Wire

      • HDSL

    • Six Wire

      • HDSL


Modulation
Modulation

  • Carrierless Amplitude-Phase Modulation (CAP)

  • Discrete Multi-Tone (DMT)

  • 4B3T - 16 codes mapped onto 27

  • 2B1Q - 4 codes mapped onto 4

  • Others

4B3T

2B1Q


Frequency spectrum g 992 1 dmt

25 Channels Upstream

<255 Channels Downstream

POTS

4.3125 kHz

4

26

Upstream Rates: 16 - 1600 kbit/s

Downstream Rates: 32 - 16320 kbit/s

Frequency Spectrum G.992.1 DMT

  • 16 bits/symbol

  • 4 Kbaud/tone

  • 64 Kbit/s/tone

1104 f(kHz)


Technical problems
Technical Problems

  • Cross Talk

  • Interference

    • Impulse Noise

    • Radio Noise

  • Line Impairments


Cross talk

Near End & Far End

Increase with Frequency

Decrease with Separation

NEXT is the biggest problem

Increasing Power doesn’t help!!

Solutions

Reduce Coupled Power

Reduced Rates

Reduced Reach

Frequency Separation

Spectral Masking

Spatial Separation

Asymmetric Rates

NEXT

FEXT

Cross Talk


Impulse noise

Noise Sources

Local in Time

Spread in Frequency

e.g. from POTS signaling

Solution (for G.992.1)

Add Redundancy

Forward Error Correction

Read-Solomon Coding

Trellis Coding

Spread the Signal

Various Interleave Depths

1  256 (x 250ms frames)

250ms  64ms Delay

Increase Received Power

Reduce Reach

Impulse Noise


Radio noise

Noise Sources

Local in Frequency

Spread in Time

eg Radio Stations

eg Other Transmitters

Solutions

Spectrum Negotiation

ie During Start-up

Dynamic Rate Adaptation

Increase Received Power

Reduced Reach

Radio Noise


Line impairments

Bridge Taps

Cause Attenuation

Loading Coils

Block higher frequencies

Split Pairs

Electrical Imbalances

Impedance Imbalance

Increases Noise

Solutions

Select good Lines

Reduce Reach

Spectrum Negotiation

Line Impairments


Typical applications

Digital Loop Carrier

Scarcity of good pairs

Pair Gain with virtual lines

High Speed Modems

Business Data Applications

Residential Data Applications

WAN Access

Branch offices

Small Campuses

ATM, Frame Relay

FDDI, SMDS

PABX access

Branch Offices

Small Campuses

T1/DS1, E1

Typical Applications


Emerging technologies
Emerging Technologies

  • Voice over DSL (VoDSL)

    • Broadband Loop Emulation Service (BLES)

    • PABX Extension

    • Voice over Multi Service Data Services (VMSDS)

  • Symmetrical DSL

    • SHDSL, HDSL2, VDSL

  • Network Management

    • Integrated ILEC, CLEC, ISP

    • Out of Box Plug and Play


Vodsl issues
VoDSL Issues

  • Which Service Types?

    • POTS, CCS, CLASS, CENTREX, IN, AIN

  • Delay Limits?

    • Interleaving, ISDN time-out risk

  • Lifeline Service?

    • Remote Power Feed

  • Signaling?

  • Network Interface?

    • PSTN (V5.1, V5.2, GR.303, TR.008)

    • B-ISDN (Circuit Emulation)


Market status
Market Status

  • Systems

    • 53 Announced Trials

    • 80 Service Deployments

  • Market Information

    • 35 million homes passed

    • 100K installed modems

    • 800M installed copper pairs

    • 170 ISPs offering DSL in USA

  • 70% of World does NOT have Cu-pair

    • ?? Mobile Technology ??


Supercom 99
Supercom’99

  • ADSL Interoperability Stand

    • 14 DSLAM Vendors

    • 25 CPE Vendors

    • ~35 Market Announcements

  • ~25-30 CPE Vendors displaying

  • ~15-20 DSLAM Vendors displaying

  • ~10 ISP’s displaying“Everyone was showing Video”


More information
More Information

  • ADSL Forum

    • Moving to a generic focus (DSL Forum)

    • http://www.adsl.com

  • Technology overview pages

    • http://www.aspergantis.com/adsl/index.htm


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