ecs5365 invited lecture overview of digital subscriber line james kershaw transmission systems...
TRANSCRIPT
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