DSL intro-3

7/30/2019 DSL intro-3

1/62

Stein Intro xDSL 3.1

Introductionto

xDSL

Part III

Yaakov J. Stein

Chief Scientist

RAD Data Communications

7/30/2019 DSL intro-3

2/62


Introduction to xDSL

I Background

history, theoretical limitations, applications

II Modems

line codes, duplexing, equalization,

error correcting codes, trellis codes

III xDSL - What is x?

x=I,A,S,V - specific DSL technologies

competitive technologies

7/30/2019 DSL intro-3

3/62


Quick recap

Lecture 1

How did we get to where we want to go?

How far canwe go?

Lecture 2

How can we get there?

Lecture 3

How can we get there?

What do we do when we get there?

7/30/2019 DSL intro-3

4/62


Quick Review

DSL leaves concept of using 4KHz analog line

Use UTP as general transmission line

Rate limited by

line loss thermal noise

NEXT crosstalk

FEXT crosstalk

RF ingress (AM broadcast, ham, etc.) misc (splices, bridged taps, echo, filters, sync)

7/30/2019 DSL intro-3

5/62


Introduction to xDSL III

Applications

Deployment topologies

IDSL

HDSL, HDSL2, SDSL

ADSL, G.lite

VDSL

competitors (cable modems,wireless)

HPNA

7/30/2019 DSL intro-3

6/62


The Baby Bells had a problem ...

1993: cable TV companies started offering10 Mbps Internet access

Internet seen as potential future market

RBOCs Plan: HFC to every home by 1996!

This didnt happen

costs grew

regulatory problems

no standardization

LECs had lower operating expenses

What could be done?

7/30/2019 DSL intro-3

7/62Stein Intro xDSL 3.7

Telco Alternatives

Fiber, coax, HFC

COST: $10K-$20K / mile

TIME: months to install

T1

COST: >$5K/mile for conditioning

TIME: weeks to install

DSL

COST: 0 (just equipment price)

TIME: 0 (just setup time)

7/30/2019 DSL intro-3


Analog (or V.90) modems

UTP subscriber line

CO SWITCH

network/ISP

router

modem

PSTN

modem

CO SWITCH

7/30/2019 DSL intro-3


xDSL System Reference Model

POTSSPLITTER

UTP

CO SWITCH

DSLAM

xTU-C

network/ISP

router xTU-R

POTS

SPLITTER

PSTN

PDN

POTS-RPOTS-C

WAN

x = H, A, V, ...

Analog

modem

7/30/2019 DSL intro-3


VoDSL

POTSSPLITTER

UTP

CO SWITCH

DSLAMxTU-C

network/ISP

routerxTU-R

POTS

SPLITTER

PSTN

PDN

POTS-RPOTS-C

WAN

7/30/2019 DSL intro-3


Network Reference Model

PDN (Premises Distribution Network) is ethernet or USB

WAN is typically ATM or FDDI (even though FDDI is LAN protocol)

Internet is TCP/IP

HDSL connects to DACS and to CSU

Many interconnect possibilities (may impact modem design)

full STM, full ATM, full packet network, packet-ATM-packet, etc.

Example, FR WAN, ATM over UTP, Ethenet PDN

Modems should be cell pumps, not bit pumps

(also need CIF protocol to tunnel ATM through Ethernet)

7/30/2019 DSL intro-3


Splitter

Splitterseparates POTS from DSL signals

Must guarantee lifeline POTS services!

Hence usually passive filter

Must block impulse noise (e.g. ring) from phone into DSL

ADSLforum/T1E1.4 specify that splitter be separate from modem

No interface specification yet (cant buy splitter and modem from different vendors)

Splitter requires installation Costly technician visit is the major impediment to deployment

G.lite is splitterless ADSL

7/30/2019 DSL intro-3


xDSL - Maximum Reach

7/30/2019 DSL intro-3


Examples of Realistic Reach

More realistical design goals (splices, some xtalk)

1.5 Mbps 18 Kft 5.5 Km (80% US loops)

2 Mbps 16 Kft 5 Km

6 Mbps 12 Kft 3.5 Km (CSA 50% US loops)

10 Mbps 7 Kft 2Km

13 Mbps 4.5 Kft 1.4 Km

26 Mbps 3 Kft 900 m 52 Mbps 1 Kft 300 m (SONET STS-1 = 1/3 STM-1)

7/30/2019 DSL intro-3


xDSL flavors

modem speed reach main applications

IDSL 160 (144) Kbps 5.5 km POTSreplacement,videoconferencing,Internet access

HDSL 2 Mbps (4-6W) 3.6-4.5 km T1/E1 replacementPBX interconnect,FR

HDSL2 2 Mbps (2W) 3 km same as HDSL

SDSL

7/30/2019 DSL intro-3


xDSL flavors

modem speed reach main applications

ADSL 8 Mbps DS 3.5-5.5 km residential Internet,video-on-demand

G.lite 1 Mbps DS 5.5 km Internet access,VoIP

VDSL

7/30/2019 DSL intro-3

17/62


ITU G.99x standards

G.991 HDSL (G.991.1 HDSL G.991.2 SHDSL)

G.992 ADSL (G.992.1 full rate G.992.2 G.lite G.992.3,4,5 new)

G.993 VDSL

G.994 HANDSHAKE

G.995 GENERAL (INFO)

G.996 TEST

G.997 PLOAM

G.998 PNT (HPNA)

7/30/2019 DSL intro-3

18/62


Some xDSL PSDs

F(MHz)

PSD(dBm/Hz)

IDSLT1

HDSL HDSL2

ADSL

7/30/2019 DSL intro-3

19/62


Line Codes

PAM IDSL, HDSL (2B1Q)

HDSL2 (with TCM and optionally OPTIS)

SDSL

QAM/CAP proprietary HDSL/ADSL/VDSL

DMT

ADSL

G.lite

VDSL line code war is still raging (but QAM seems to be winning)

7/30/2019 DSL intro-3

20/62


T1/E1

DS1 rate

1 bit per symbol AMI

Half duplex on each UTP

Full duplex requires 2 UTP (4W)

Simple DSP

Linear equalization

Needs conditioning

Repeaters (every km)

7/30/2019 DSL intro-3

21/62


IDSL

Original DSL (1980s)

160 Kbps in 80 KHz BW

resistance design reach (18Kft)

popular in Europe, but not US

2 bit PAM called 2B1Q (2 Bits in 1 Quat)

10 +3 (Gray code)

11 +1

01 -1

00 -3

alternative line code:

4B3T (4 Bits in 3 Ternary symbols)

+3

+1

-3

-1

7/30/2019 DSL intro-3

22/62


HDSL

Replace T1/E1 DS1 service

Use 2B1Q line code, DFE

Full duplex on each pair with echo cancellation

Full CSA without conditioning/repeatersmore complex DSP (250 MIPS)

ANSI: 2 pairs for T1 (each 784 Kbps)

ETSI: 1, 2, 3 or 4 pairs

Most mature of DSL technologies

7/30/2019 DSL intro-3

23/62


HDSL vs T1(AMI)

T1

HDSL

7/30/2019 DSL intro-3

24/62


HDSL - continued

HDSL is repeaterless T1/E1

Major application - multiline POTS

Reach is CSA (less than ADSL!)

Can add doublers to extend range

Other applications:

PBX extension

digital local loop campus networks

Internet

7/30/2019 DSL intro-3

25/62


HDSL2, SDSL, SHDSL, OPTIS

Customers request HDSL service that is single UTP HDSL

at least full CSA reach

spectrally compatible w/

HDSL, T1, ADSL, etc.

Variously called

HDSL2 (ANSI)

SDSLSymmetricDSL (ETSI)

SHDSL Single pairHDSL (ITU)

This is the DS1 service that will last!

7/30/2019 DSL intro-3

26/62


OPTIS Overlapping PAM Transmission with Interlocking Spectra

A solution that achieves these goals

16 level PAM with 517K baud rate

very strong (512 state, >5 dB) TCM

1D for low (216 sec) latency (speech)

strong DFE

tailored spectra (fits between HDSL and T1)

partially overlapped (interlocking) spectra

folding (around fb/2) enhances SNR!

upstream bump for spectral compatibility

7/30/2019 DSL intro-3

27/62


OPTIS - continued

7/30/2019 DSL intro-3

28/62


OPTIS - continued

7/30/2019 DSL intro-3

29/62


ADSL

Asymmetric - high rate DS lower rate USOriginally designed forvideo on demand

Almost retired due to lack of interest

but then came the Internet

Studies show DS:US should be about 10:1full rate ADSL 512-640 kbps US, 6-8 Mbps DS G.lite 512 Kbps US, 1.5 Mbps DS

ADSLcould meanAll Data Subscribers Living

7/30/2019 DSL intro-3

30/62


Why asymmetry?

NEXT is the worst interfererstops HDSL from achieving higher rates

FEXT much less (attenuated by line)

FDD eliminates NEXT

All modems must transmit in the SAME direction

A reversal would bring all ADSL modems down

Upstream(US) at lower frequencies and power density

Downstream (DS) at high frequencies and power

7/30/2019 DSL intro-3

31/62


Why asymmetry? - continued

US

DS

PSD (dBm/Hz)

F(MHz)

7/30/2019 DSL intro-3

32/62


Echo cancelled ADSL

FDD gives sweet low frequencies to US only

and the sharp filters enhance ISI

By overlapping DS on US

we can use low frequencies and so increase reach

Power spectral density chart

7/30/2019 DSL intro-3

33/62


ADSL - continued

ADSL system design criterion BER 10-12 (1 error every 2 days at 6 Mbps)

Raw modem can not attain this low a BER!

For video on demand:

RS and interleaving can deliver (error bursts of 500 msec) but add 17 msec delay

For Internet:

TCP can deliver high raw delay problematic

So standard defines TWO framers

fast (noninterleaved ) and slow (interleaved) buffers

7/30/2019 DSL intro-3

34/62


ADSL standard

ITU (G.dmt) G.992.1, ANSI T1.413i2 standard

First ADSL data implementations were CAP

Standard is DMT

DMT allows approaching water pouring capacity

DMT is robust

DMT requires more complex processing

DMT may require more power

7/30/2019 DSL intro-3

35/62


DMT

Discrete Multitone is a form ofFDM (Frequency Domain Multiplexing)

Discrete Multitone is a form ofMCM (MultiCarrierModulation)

It uses many different carriers, each modulated QAM

Each tone is narrow

low baud rate (long frame)

channel characteristics are constant over tone

Number of bits per tone chosen according to water pouring

Put more bits where SNR is good

7/30/2019 DSL intro-3

36/62


DMT - continued

DMT is OFDM (Orthogonalized FDM) Carrier spacing is precisely baud rate

Center of tone is precisely the zero of all other sincs

ICI minimized

ISI minimized by having a long interframe guard time

DMT modem can be efficiently implemented using FFT

DFT is mathematically equivalent to a bank of filters

Filtering is equivalent to cyclic convolution

So use cyclic prefix rather than guard time

7/30/2019 DSL intro-3

37/62


DMT - continued

time

frequency

7/30/2019 DSL intro-3

38/62


ADSL DMT

Baud rate (and channel spacing) is 4.3125 KHz

US uses tones 8 - 32 (below 30 KHz reserved)

DS uses 256 tones (FDM from tone 33, EC from tone 8)

P

O

T

S

US DS

8 32 256

7/30/2019 DSL intro-3

39/62


DMT misc.

bit handling((de)framer, CRC, (de)scrambler, RS, (de)interleaver)

tone handling (bit load, gain scaling, tone ordering, bit swapping)

QAM modem (symbolizer, slicer)

signal handling (cyclic prefix insertion/deletion, (I)FFT,

interpolation, PAR reduction)

synchronization (clock recovery)

channel handling (probing and training, echo cancelling, FEQ, TEQ)

7/30/2019 DSL intro-3

40/62


RADSL

RateAdaptive ADSL

Not variable rate (not small fast variations)

Increases percentage of useable lines

Fine for Internet access

but not for video on demand

Standard ADSL supports 32Kbps steps

RADSL provides management protocols

7/30/2019 DSL intro-3

41/62


G.lite

ITU (G.lite) G.992.2, UAWG

ADSL compatible DMT compatible using only 128 tones

512 Kbps US / 1.5 Mbps DS

Still much faster than V.34 or V.90 modems

No splitter required!

Certain features removed for simplicity

simpler implementation (only 500 MIPS < 2000 MIPS for full rate)

7/30/2019 DSL intro-3

42/62


New ADSLs

ITU has continued development of G.dmt.bis, G.lite.bis

Should become G.992.3, G.992.4, G.992.5

ADSL2

Longer reach with higher rate (1.5 Km @ 12 Mbps)4D 16-TCM constellations, Stronger RS FEC

Lower framing overhead (programmable 4-32Kbps overhead)

Power cutback standby mode

Algo improvements (e.g. real-time tone re-ordering, relocatable pilot tone)

ADSL+

Uses more BW for higher bitrates for short reaches

double BW (512 bins) - double speed (24 Mbps!)Annex J

Symmetric 3 Mbps

7/30/2019 DSL intro-3

43/62


VDSL

Optical network expanding (getting closer to subscriber)

Optical Network Unit ONU at curb or basement cabinet

FTTC (curb), FTTB (building)

These scenarios usually dictates low power

Rates can be very high since required reach is minimal!

Proposed standard has multiple rates and reaches

7/30/2019 DSL intro-3

44/62


VDSL - rate goals

Symmetric rates6.5 4.5Kft (1.4 Km)

13 3 Kft (900 m)

26 1 Kft (300 m)

Asymmetric rates (US/DS)

0.8/ 6.5 6 Kft (1.8 Km)

1.6/13 4.5 Kft (1.4Km)

3.2/26 3 Kft (900 m)

6.4/52 1 Kft (300 m)

7/30/2019 DSL intro-3

45/62


VDSL - Power issues

Basic template is -60 dBm/Hz from 1.1MHz to 20 MHz

Notches reduce certain frequencies to -80 dBm/Hz

Power boost on increase power to -50 dBm/Hz

Power back-offreduces VTU-R power so that wont block another user

ADSL compatibility offuse spectrum down to 300 KHz

7/30/2019 DSL intro-3

46/62


VDSL - duplexing

In Japan and campus applications can operate TDD (ping pong)

SDMTSynchronous DMT

(2 KHz frame can be heard in adjacent pairs or hearing aids)

Rest of world PSTN only FDD is allowed

Can divide US and DS into 2 areas (e.g. ADSL) or more

Need guard frequencies because of clock master/slave problems

Zipper- large number of interleaved frequency regions(even on a bin by bin basis)

7/30/2019 DSL intro-3

47/62


VDSL line code wars

VDSL Alliance VDSL CoalitionDMT QAM

MORE LESS

robust to noise powercapacity complex

spectral compatibility expensive

IPR A/D bits

With no complexity constraints probably equivalent

7/30/2019 DSL intro-3

48/62


T1E1.4 draft T1.424

T1E1.4 has released a 3-part trial use draft standard

Part 1 Common Specifications

Part 2 Single Carrier Modulation

Part 3 Multicarrier Modulation

Objective tests have been specified (VDSL Olympics) Test definition may determine results

SCM is NOT spectrally compatible with ADSL

Present SCM implementations are more mature

the tests should be of technology, not products

MCM may be more robust in certain noise settingsThe trials should be finished by July-August 2003

ITU and IEEE are waiting for the results

7/30/2019 DSL intro-3

49/62


G.994.1 (G.hs)Handshaking

Universal flexible method for initialization

Includes

tone negotiation for capability identification

common mode identification exchange of nonstandard information

line probing (line code dependent)

Currently integral part of ADSL and G.liteAnticipated that future ITU DSL modems will support as well

7/30/2019 DSL intro-3

50/62


G.997 (PLOAM)Physical LayerOperationAdministration and Maintenance

Includes

physical layer management (SNMP based)

configuration, fault and performance administration

4 management interfaces optional OAM channel

far end management

Currently integral part of G.992 (ADSL) family

Anticipated that future ITU DSL modems will support as well

7/30/2019 DSL intro-3

51/62


G.996.1 (G.test)Universal testing procedure for xDSL modems

Finds margins in presence of

POTS signaling

impulse noise

cross-talk from other services

geographical position dependent test loops and wiring models

Currently integral part of G.992 (ADSL) family

Anticipated that future ITU DSL modems will support as well

7/30/2019 DSL intro-3

52/62


G.bond

ISDN defined BONDING of 2B channels to one 128Kbps line

G.991.2 (SHDSL) Annex E has physical layer bonding

ITU G.bond objectives:

1) be higher layer agnostic

2) be backward compatible with the present 2-wire G.shdsl Annex E solution

3) different rates on different pairs4) be applicable to all DSL families, not just SHDSL

5) have low latency and overhead (to support TDM)

6) support dynamic addition and removal of pairs

If succeeds no need for layer 2+ aggregation protocols

(ATM-IMA, MLFR, MLPPP, 802.3ad etc) withhigh overhead, high latency, same rates for each pair,

no dynamic addition/deletion support, etc.

7/30/2019 DSL intro-3

53/62


cVoDSL

Standard VoDSL sends TDM over ATM layerChannelized VoDSL reserves N 64Kbps channels (N=1..4)

PRO Implemented on-chip (no GW), higher voice quality, lower delay

CON Consumes BW even if not used

baseband physical layerPOTS

cVoDSL DSL physical layer

ATM layer

AAL1 AAL2 AAL5

IP layer

VoATM

VoIP

7/30/2019 DSL intro-3

54/62


Competitors

andnon-DSL

technologies

7/30/2019 DSL intro-3

55/62


G.998 (G.pnt,HPNA)

Studies show that about 50% of US homes have a PC

30% have Internet access, 20% have more than one PC!

Average consumer has trouble with cabling

HomePNA de facto industry standard for home networking

Computers, peripherals interconnect (and connect to Internet?)

using internal phone wiring (user side of splitter)

Does not interrupt lifeline POTS services

Does not require costly or messy LAN wiring of the home Presently 1 Mbps, soon 10 Mbps, eventually 100 Mbps!

7/30/2019 DSL intro-3

56/62


HPNA

HPNA 1.0 (98Q3) has average data rate 1.0432 Mbps

Line code is PPM (pulse position modulation)

Each pulse is 4 cycles at 7.5 MHz (shaped)

time between pulses 3.27 msec < t < 6.07 msec

Can co-exist with full-rate ADSL and G.lite

HPNA 2.0 (ITU G.pnt) 10 - 32 Mbps

QAM line code

HPNA 3.0 up to 100 Mbps Specification not yet finalized

7/30/2019 DSL intro-3

57/62


Cable modems

CATV

HEADEND

OPTICAL

FIBER

NODE

COAXIAL

AMPLIFIER

CABLE

MODEM

CABLE

MODEM

CABLE

MODEM

CABLE

MODEM

fiber coax

CMTS

7/30/2019 DSL intro-3

58/62


Cable modems - continued

Line Code (nonstandard, IEEE 802.14)

QPSK/16 QAM US 1.5 Mbps (raw)

64/256 QAM DS 30 Mbps (raw)

QPSK control channel

FDD (US low frequencies, DS high frequencies)

BW to CM is shared

Performance degrades when too many users

7/30/2019 DSL intro-3

59/62


Cable modems - continuedDOCSIS - Data OverCable System Interface Specification

Evolving specification for high-speed data-over-cable systems

DOCSIS 1.0 designed for transparent bi-directional IP traffic 3.2 MHz channel, 5.12 Mbps (QPSK)

DOCSIS 1.1 enhancement:

3.2 MHz channel, 10.24 Mbps (16-QAM) BW management features for QoS multimedia applications

DOCSIS 2.0 improved modem 6.4 MHz channel, 30.72 Mbps (64-QAM / 128-QAM+TCM / S-CDMA)

symmetric upstream and downstream,

increased noise immunity

Cable modems are not allowed to monitor each other

so Ethernet (CSMA/CD) is not possible

7/30/2019 DSL intro-3

60/62


MMDS

Wireless cable services are only minor competition

Services originated when telcos wanted to get into CATV

Multichannel Multipoint Distribution System (Wireless CATV) 2.6 GHz (SHF) frequencies

54 Mbps DS (33 uncompressed video/data channels)

Upstream traffic requires expensive subscriber transmitters

Line of site range

Technical problems: weather, trees

7/30/2019 DSL intro-3

61/62


LMDS

LocalMultipointDistributionSystem (Cellular TV)

28 GHz frequency

short-distance version of MMDS

uses small cells

small cell size requires many transmission antennas

most suitable for business LAN extension

7/30/2019 DSL intro-3

62/62

DBS

Direct Broadcast Satellite

Geosynchronous satellites already used for digital TV

POTS return connection

High powered transmitter return connection Significant propagation delay

Low earth orbit (LEO) satellites

Minimal delays Lower power uplink transmitters

Too expensive for residential use

DSL intro-3

Documents

Transcript of DSL intro-3