ECS5365 Invited LectureOverview of Digital Subscriber Line

James KershawTransmission Systems Division

NEC Australia Pty Ltdhttp://www.nec.com.au

Agenda

What is Digital Subscriber Line?StandardizationDSL ArchitectureTechnical IssuesTypical Applications

Digital Subscriber Line

Modem based Access TechnologyExisting Subscriber InfrastructureHigher Speed ConnectionsPair Gain Capability

Advantages of DSL

Point to Point Connection Dedicated bandwidth Inherent Security

Existing Infrastructure Reduced roll-out costs

Cheaper Operating Costs

Perform

ance

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

Standardization

What needs to be standardized?Who is involved with Standardization?What standards exist?

What needs to be standardized?

Physical InterfacesElectrical InterfacesLink Layer BehaviourNetwork Layer BehaviourSignaling and NegotiationTest ProceduresElectrical Compatibility

Who is Involved

National Bodies eg. ANSIRegional Bodies eg. ETSIInternational Bodies eg, ITU-T, IETFSpecial Interest Groups eg. ADSLF, ATMF

International DSL Standards

ITU-T StandardsG.991 (G.hdsl) - T1/E1 symmetricG.991.2 (G.shdsl) - under studyG.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/sG.993 (G.vdsl) - under studyG.994.1 (G.handshake) - DSL Negotiation

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

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

Reference ArchitectureMediumModulationSpectrumTypical Configurations

Reference Architecture (ADSLF)

ServiceProvider

RegionalBroadband

Network

AccessNode

NetworkTermination (B-NT)

CustomerPremisesNetwork

CustomerPremises

Equipment

A11 A10 V U T S

Core Network

A11, A10 are from DAVICV,U,T, S are from ITU-T

Core

NTUAccessServer

SDH

ATM

ADSL

ATM

10BaseT

AccessMultiplexer

DSL Medium

Twisted Pair Two Wire

ADSL, IDSL, SDSL, HDSL2, VDSL

Four WireHDSL

Six WireHDSL

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

1104 f(kHz) 4

4.3125 kHz

26

25 Channels Upstream

<255 Channels

DownstreamPOTS

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

Technical Problems

Cross TalkInterference

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!!

NEXT FEXT

Solutions Reduce Coupled

PowerReduced RatesReduced Reach

Frequency SeparationSpectral Masking

Spatial SeparationAsymmetric Rates

Impulse Noise

Noise Sources Local in Time Spread in Frequency e.g. from POTS

signaling

Solution (for G.992.1) Add Redundancy

Forward Error CorrectionRead-Solomon CodingTrellis Coding

Spread the SignalVarious Interleave Depths

• 1 256 (x 250ms frames)

• 250ms 64ms Delay

Increase Received PowerReduce Reach

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

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

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

Emerging Technologies

Voice over DSL (VoDSL)Broadband Loop Emulation Service (BLES)PABX ExtensionVoice over Multi Service Data Services (VMSDS)

Symmetrical DSLSHDSL, HDSL2, VDSL

Network ManagementIntegrated ILEC, CLEC, ISP Out of Box Plug and Play

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

Systems53 Announced Trials80 Service Deployments

Market Information35 million homes passed100K installed modems800M installed copper pairs 170 ISPs offering DSL in USA

70% of World does NOT have Cu-pair?? Mobile Technology ??

Supercom’99

ADSL Interoperability Stand14 DSLAM Vendors25 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

ADSL Forum Moving to a generic focus (DSL Forum) http://www.adsl.com

Technology overview pages http://www.aspergantis.com/adsl/index.htm