asymmetric digital subscriber line
DESCRIPTION
Asymmetric Digital Subscriber Line. BROADBAND APPLICATIONS. PC HOUSEHOLDS. ADSL CONFIGURATION. SPEED SHRINKS WITH DISTANCE. LINE CODES. DSL BROADBAND TECHNOLOGIES. LINE CODES. DMT OR CAP?. DSL: A POINT-TO-POINT SOLUTION. TWO-DIMENSIONAL LINE ENCODING. CAP TRANSCEIVER ARCHITECTURE. - PowerPoint PPT PresentationTRANSCRIPT
Asymmetric DigitalSubscriber Line
A 10-billion unit m arket induced byInternet!
D riving force: The A D SL ForumG etting 10M B /s to hom es,using telephone linesForm al education is oftentim es m isleading!?
W ho w ins: D iscrete M ultiTone (D M T)orC arrierless A m plitude/Phase(C A P)?
Success story: B ay N etw orks
BROADBAND APPLICATIONS
Entertainment Broadcast TVVODInternet—Text 0.014–6 MbpsInternet—Graphics 0.5–6 MbpsGambling 0.014–2 MbpsGames 0.014–16 Mbps
Consumer Shopping 0.5–6 MbpsEducation 0.5–6 MbpsEducation 1.5–6 Mbps
Professional Work at Home 0.014–6 MbpsSOHO 0.014–6 MbpsVideo Conf 0.128–1.5 Mbps
NT = Network Terminal (aka Gutless PC)
PC HOUSEHOLDS
0102030405060708090
100
1995 1996 1997 1998 1999 2000
PC Households WorldwideConnected PC Households Worldwide
ADSL
ADSL CONFIGURATION
SwitchedTelephone
NetworkModemModem
Line card filtersdetermine bandwidth
4 kHz Vioce ChannelData limited to 33 kbps
ATMBroadband
NetworkServiceADSL
Local loopdetermines bandwidth
<1 MHz bandwidthrates to 52 Mbps,
depending on length
ADSL
SPEED SHRINKS WITH DISTANCE
10
20
30
40
50
3 6 9 12 15 18
VDSL
ADSL
Dominant impairment—AttenuationAttenuation increases with distance and frequencySecondary impairments—Cross Talk, Impulse noise, Bridged TapsSpectrum used— DSL 100 kHz
HDSL 250 kHzADSL 1 MHzVDSL 10–30 MHz
Distance in kft of 24 (.5 mm) ga wire
DSL BROADBAND TECHNOLOGIESHDSL 1.5/2.0 Mbps symmetric
T1/E1 service only (2/3 lines, no FEC)
SDSL 1.5/2.0 Mbps symmetricT1/E1 rates on single line over POTSSuitable for residential services
ADSL 1.5–9.0 Mbps, asymmetric (640 max upstream)Single line over POTSFEC, multiple premises interfacesCircuit, packet and ATM multiplexing
VDSL Current View 13–52 Mbps, asymmetric (3 Mbos upstream)Emerging View 16–26 Mbps down, 6 Mbps up (PC symmetric)Single line over POTS and ISDNRest in the air
DSL = Digital Subscriber Line, H = High, S = Single line, A = Asymmetric, V = Very high rate
LINE CODES
Two general alternatives in marketplace today
QAM/CAP—single carrier (like voice band modems)
10,000 in field trialsHelped prove ADSL concept
DMT—Discrete MultiTone
ANSI standard1000 in field trialsHelped prove ADSL to 6 Mbps
DSL BROADBAND TECHNOLOGIES
ADSL 1.5–9.0 Mbps, asymmetric (640 maxupstream)Single line over POTSFEC, multiple premises interfacesCircuit, packet and ATM multiplexing
VDSL Current View 13–52 Mbps, asymmetric(3 Mbos upstream)Emerging View 16–26 Mbps down, 6Mbps up (PC symmetric)Single line over POTS and ISDNRest in the air
DSL = Digital Subscriber Line, H = High, S = Single line, A =Asymmetric, V = Very high rate
LINE CODES
Two general alternatives in marketplace today
QAM/CAP—single carrier (like voice band modems)
10,000 in field trialsHelped prove ADSL concept
DMT—Discrete MultiTone
ANSI standard1000 in field trialsHelped prove ADSL to 6 Mbps
DMT OR CAP?Both will work.But cannot be made to interoperate
DMT Benefits: 32 kbps rate granularity (CAP at 320 kbps)Probably works on more linesGreater immunity to impulse noiseSpectral management toolANSI standard (ergo, 5 silicon efforts underway)
CAP Benefits: Dominated field trials to dateHigher level of integration, nowWell understoodSupported by some major playersInteroperable with QAM
With equal levels of integration, complexity and power appear comparable.
Time is of the essence in the market
Stay tuned!
DSL: A POINT-TO-POINT SOLUTION
Point-to point DSL LinkAcross the Local Loop (i.e.
from the customer premises tothe CO)
Local Area Domain (i.e. fromthe ATU-R to either corporate
LAN or residential user)
Network Access Provider'sDomain (i.e. from the ATU-Cat the CO to various network
services—Frame Relay, ATM,Internet, etc.)
Customer'sNetwork
AccessProvider'sNetwork
ATU-C
ATU-C
ATU-R
ATU-R
NetworkInterfaces*
NetworkInterfaces*
ResidentialTerminal
ATU-C = DSL modem in the COATU-R = DSL modem at the service subscriber’s premises
* Network interface: DSL equipment on both sides of the link (i.e., both the ATU-R andATU-C) have network interfaces to connect to the access provider’s and customer’s
networks. These interfaces may include Ethernet, Fast Ethernet, ATM, T-1/E-1, ISDN,Frame Relay, or others
TWO-DIMENSIONAL LINE ENCODING
0
1
One-dimensionalBinary
Line Code
00
Two-dimensionalBinary
Line Code
0111
10
x
y
Amplitude
–T/2 +T/2 –T/2
+T/2
Amplitude
Signal x Signal y
SymbolPeriod
B IT M A P P IN G C O N S T E L L A T IO N SF O R A T W O -D IM E N S IO N A L L IN E C O D EA N D 6 4 -C A P
Bit MappingConstellation for aTwo-Dimensional,Binary Line Code
Bit MappingConstellation for 64-CAP
(a Two-Dimensional,Multilevel Line Code)
x
y
1
x
y
UPSTREAM AND DOWNSTREAMCHANNELS IN CAP SYSTEMS
Two WireTwisted Pair
AmplitudeSpectra
CAP
ExistingTelephone
Service
DuplexTransmission
and Control Channel
SimplexTransmission
Control Channel
4 kHz f1(low)
f1(high)
f2(low)
f2(high)
frequency (kHz)
CAP TRANSCEIVER ARCHITECTURE
Reed-SolomonEncoder w/Interleaving
ScramblerTrellis
EncoderChannelPrecoder
CAPTransmitter
D/A Tx FilterLine
Driver
Rx FilterEqualizer A/D AGCViterbi
Decoder
Symbol-to-BitMap
De-Scrambler
DownstreamData
UpstreamData
CAP Receiver Architecture
CAP Transmitter ArchitectureDigital Signal Processing Analog Front End
Hybrid Line
DMT’S UTILIZATION
FREQUENCY SPECTRUM AVAILABLE ON ASINGLE TWISTED PAIR WIRE(I.E., TELEPHONE CABLE)
AmplitudeSpectra ofSingle PairUTP Cable
DMT
ExistingTelephone
Service
256 Sub-Channels
4 kHz
frequency (kHz)4 kHz Intervals
1 MHz
DMT TRANSMITTER AND RECEIVER
ARCHITECTURES
BitBuffer
andEncoder
2n timedomainsamples
ADC S/P
FastFourier
Transform(FFT)
LPFn QAM
SymbolsReceiveSignal
ReceiveData
BitBuffer
andEncoder
InverseFast
FourierTransform
(IFFT)
P/S DAC LPFTransmit
SignalInput Data
2n timedomainsamples
n QAMSymbols
2n/T
2n/T
DMT Transmitter Architecture
DMT Receiver Architecture
MYTH VS. REALITY
Myth Reality
1. DMT has higher consumption than CAP. 1. For equivalent rates CAP requires more power than DMT.2. DMT was intended for Video on Demand (VoD) and has
been made obsolete by Internet access.2. DMT is very well suited for Internet support. The ANSI
standard explicitly addressed data access. The upstreamrate was chosen to reflect the 10:1 ratio that is optimum forInternet traffic.
3. CAP invented rate adaptation. 3. DMT has always been rate adaptive, takes it for granted, andimplements it in a highly flexible and elegant way. Indeed, thecoarse granularity of CAP (steps of ~300 kbps and nodownstream rates of less than 640 kbps) renders its rateadaptation essentially useless for rural low-rate/long-reachapplications. In contrast DMT steadily adapts in 32 kbpssteps to support optimum rates on all loops.
MYTH VS. REALITY
1. Performance is equivalent. 1. DMT is demonstrably more robust and has much betterperformance—delivering higher rates, much longer reach, orboth.
2. DMT is heavily patented or inaccessible. 2. DMT is defined in an open international standard mandatingfair access. Many manufacturers have independentlydeveloped their own solutions. It is the CAP technology hasremained proprietary and with only one supplier.
3. DMT is less available than CAP. 3. Solutions designed to the ANSI standard are available nowfrom several suppliers: there is only source of CAS chipsets,and this will ot comply with proposed future definition.
ADSL modems versus cable modems:Cable - 3Mbps (popular rate)ADSL - 9Mbps/downstream and 1Mbps/upstream (popular rates)
Issues in cable technology (speed and price):Getting faster and less expensive (better SNR, economies of scale, ...)IEEE 802.14 (cable TV metropolitan area network standard)
Issues in ADSL technology (very high speeed versus universal):Orckit Communications offers very high speed DSL (52Mbps vs 13Mbps)Microsoft (2000) Comcast $1B investment for UADSL (1.5Mbps vs 512Kbps)
Comparative dissadventages of ADSL:a. A 4KHz splitter needed to separate voice from ADSL (not if cable used)b. I-structure additions less widespread (modifications needed in PBX)c. More expensive ($40 to $80 vs $40 = analog modem + second line)d. More attractive for business (traditional experiences of phone companies)
Comparative adventages of ADSL:a. Sending a fixed number of packets in time (not when bandwidth available)b. Less security risks (interference can be an issue in cable technology)c. All ADSL i-structure can transmit upstream (only 20% cable-i-structure)d. All homes and businesses have phone lines (cable: H=60% and B=20%)
Reference:Lawton, G., Paving the Information Superhighway's Last Mile,IEEE Computer, April 1998, pp. 10-14
Research at UB/IFACT
The VLSI point-of-view based on past experience:
1. DMT and VLSIAlgorithm versus algorithm implementation
2. The story of HFMGetting repeated once every decade! IEEE Trans/ASSP
3. The story of GaAsRanking changes when technology changes! IEEE Trans/Computers
Acknowledgments:Dejan Rašković, …