0 x dsl

All Rights Reserved © Alcatel-Lucent 2007

7302 ISAM

xDSL

Alejandro Páez

[email protected]

All Rights Reserved © Alcatel-Lucent 20072 | xDSL

Table of content

Introduction

The DSL family

Standards

Restrictions

Modulation

Error detection and correction

ADSL flavors


Introduction

TOC


POTS modem communication

WWW

NB Access server

+ modem pool

modemPSTN network

Modem to modem communication in POTS band through the PSTN network!

Frequencies within the voice band are transmitted through the switched connection of a PSTN network

This voice band is used for voice or modem communication (e.g. fax, V.32, V.90, ...)


POTS vs non-POTS modem communication

Frequency (fHz)300Hz 3400Hz

Other frequencies used by DSL technologies:

ISDN > up to 80kHz

ADSL > up to 1,1MHz

Voice band

used by

POTS modems

(V.32, V.90, …)

Spectrum of local telephone line

DSL technologies use other frequencies outside the voice band to modulate information on your local telephone line (UTP)

ISDN provides you with a 160 Kbps connection

ADSL gives you a high speed broadband connection on your local line


Solutions offered by ADSL

PROBLEM

Bitrate of analogue modem limited to 56 kb/s

PSTN not suited for high speed data

traffic

ADSL - modem

Redirection of data traffic to specific

network (B-ISDN)

SOLUTION


ADSL

7300 ASAM

POTS,ISDN

ANT

Residential

unshielded twisted pair (UTP)

upstream : up to 800 kbps

downstream : up to 8,1 Mpbs

ADSL : Digital Subscriber LineAsymmetrical

max 5,4 km


ADSL spectrum

Upstream DownstreamPOTS

300Hz

3400Hz

1,1 MHz30kHz 125 kHz 164 kHz

ADSL

POTS

Copperwire±8Mbps

±800kbps

138 kHz

ADSL uses frequencies on the local line up to 1,1 MHz

These frequencies do NOT overlap with the POTS or ISDN band, allowing simultaneous voice and data communication


POTS splitter (PS)

FILTER

SPLITTER

& UTP to LEX

The lower frequencies used by ADSL can disturb the audible spectrum and need to be filtered out towards the telephone set

With on-hook / off-hook situations, the line impedance changes and this will impact the ADSL modem communication (re-sync)


Voice / Data over DSL ?

DataStandard ADSL ADSL with “derived” voice

VoDSL CPE

Data

Telephone Line

ADSL

POTS Lifeline

PS

POTSTelephone Line

ADSLADSL CPE

PS

ADSL suitable for all types of communication (voice and data)

Evolution towards Full Digital Loop (FDL)

Elimination of POTS lifeline (and thus splitter)


ADSL overview

ISP

CorporatesNTATM

POTS

PSTN

LT

POTS

ADSL modem-modem communication

ATM PVC connection

End-to-end data connection

Service providers Access providers End users

AS (BRAS)PS PS

ADSL modem pool

LT

voice

data


The DSL family

TOC


xDSL

ADSL first approach to deliver high bandwidth over existing UTP killer technology for residential internet access

SHDSL symmetrical high bandwidth service mostly for business users

VDSL very high speed bandwidth for BB entertainment (video) can work both in symmetrical & asymmetrical mode

FTTU fiber to the user = optical fiber all the way to the customer. conquering “the last mile”


SHDSL

Single-pair High speed DSL 192 kbps … 2.312 Mbps bidirectional (Single pair UTP) 384 kbps … 4.624 Mbps bidirectional (Double pair UTP) IMA support via SMLT board : combine 8 SHDSL lines links into one

virtual link (8 x 2,312 Mbps)

Limited in distance max 2,5 km loops

No POTS/ISDN service SHDSL uses the entire frequency range no splitters required

TC/PAM modulation technique


VDSL

Bitrates up to 55Mbps downstream on short loops (300m) maximum loop reach : 1500m ± 3000 carriers for DMT

Mostly needs a non-CO deployment via remote units (FTTN : fiber to the neighborhood)

Uses frequencies up to 12MHz zipper mechanism with FDD (frequency division duplexing) standardized bandplans (next slide)

Upstream Power Back Off to avoid FEXT

Disable carriers to avoid interference with HAM bands


VDSL band plans

down up updown

down up updown

down up updown

Plan B (formerly plan 997) ETSI + ITU - compromisecompromise band plan

flexible plan Fx (ITU; under discussion in ETSI)

Plan A (formerly plan 998) ETSI + ANSI + ITU - optimized for asymmetryasymmetry

ADSL

0.138 3.0 5.1 7.05 12.0 MHz

0.138 3.75 5.2 8.5 12.0 MHz

0.138 3.752.5 Fx 12.0 MHz

0.138 1.1 MHz

example band plan for China - optimized for symmetrysymmetry

down up optional down

0.138 3.75 8.5 12.0 MHz


FTTU

Fiber To The User using PON (Passive Optical Network, passive star topology)

Extremely high bandwidth using Wavelength Division Multiplexing 622 Mbps down, 155 Mbps up

Smaller-diameter, lighter-weight cables

Lack of crosstalk between parallel fibers no NEXT, FEXT Immunity to inductive interference

High-quality transmission

Low installation and operating costs


FTTU deployment scenario

OLT

LL Network

OTHER

POTS/ISDNV5

VB5

G.703

ONUADSL ( < 6 KM )

< 8 Mbit/s

FTTEx

ONUADSL/VDSL ( < 1 KM )

< 26 Mbit/s

FTTCab

ONUVDSL ( < 300 M )

< 52 Mbit/s

FTTC

ONT

< 622 Mbit/s down

< 155 Mbit/s up

FTTH/B

Central Office

XNT

XNT

XNT

ATM NETWORK


Standards

TOC


ANSI standards

ANSI T1.413 Issue 1 1995 first ADSL specification out in 1995 was STM based and not clearly

built.

ANSI T1.413 Issue 2 1998 second ADSL specification which was mostly driven by Alcatel and

ATM based as is used today


ITU-T standards

ITU-T G.dmt or G992.1 specification by ITU-T which is based on the ANSI T1.413 Issue 2

standard plus an extra handshaking protocol. Annex A specifies operation above the POTS band Annex B specifies operation above the ISDN band Annex C specifies operation for the Japanese ISDN band

ITU-T G.lite or G992.2 specification by ITU-T which is a “stripped down” version of the ANSI

T1.413 Issue 2 standard plus an extra handshaking protocol. Based on recommendations made by the UAWC workgroup (Microsoft, Compaq, Intel)

ITU-T G.hs or G994.1 specifies the handshaking procedure for xDSL transceivers


Spectrum

UP DOWN

PO

TS

UP DOWNISDN

UP DOWN

PO

TS

30kHz

1,1MHz

1,1MHz30kHz

138kHz

548kHz

G.dmt Annex A

G.dmt Annex B

G.lite

138kHz


Restrictions

TOC


Data speed

Bits symbols bits

sec sec symbol

Question : how can we increase the data speed and respect the symbol rate related constraint ? (Nyquist)

Answer : increase the number of bits per symbol via different modulation techniques like QAM bit rate expresses in bits per second (bps) symbol rate expressed in symbols per second (baud)


Nyquist bandwidth constraint

Symbol period

For a given bandwidth (W in Hz), the maximum amount of symbols/second (Rs in baud) is limited in order to avoid Inter Symbol Interference (ISI)

Time (sec)

Ts

Each symbol corresponds to a number of bits

You need to be able to distinguish one symbol from another

The symbol period is minimum the signal period of the lowest frequency.


Shannon-Hartley capacity theorem

W = bandwidth in HzSNR = Signal to Noise ratio in dBG = Gainfactor achieved by error correction

Capacity [bps] 1/3 x W x SNR x G~~


Shannon-Hartley : Capacity vs. Distance

km

1 2 3 4 5 6UTP Cable length

CapacityMb/s

25

20

15

10

5

Shannon Hartley capacityADSL

8,1 Mb/s

2 Mb/s

6 Mb/s


Attenuation vs. Frequency

10 KHz 100 KHz 1 MHz

0

20

40

60

80

Attenuation (dB)

Frequency (Hz)

1 km

2km3km

4km

Cable cross section = 0,5mm²

POTSband

x dR =

Seff


Attenuation due to distance

Local exchange

UTP cable 0,5 mm2

4 km : Loss of 32dB at 150 kHz

Transmitted pulse Received pulse

5 km : Loss of 55dB at 150 kHz

x dR =

Seff


Speed characteristics vs. distanceM

bit

/sK

bit

/s

km0

2

4

6

8

10

0 1 2 3 4 5 6

ADSL Downstream

km0

200

400

600

800

1000ADSL Upstream


Bridged taps

Main Signal

Echo

Echo

Frequency (Hz)

Attenuation (dB) Increased attenuation due to Bridged Tap

1

32


Crosstalk

Tx

Rx

Tx

Rx

Near End Crosstalk

Far End Crosstalk

For ADSL there is no Near End Crosstalk only Far End Crosstalk!

Tx

RxRx

TxRx

Tx RxTxRx


Crosstalk AoP & AoI

UP DOWN

PO

TS

1,1MHz30kHz

G.dmt Annex A

138kHz

UP DOWNISDN

1,1MHz138kHz

G.dmt Annex B

NEXT

When AoP (ADSL over POTS) and AoI (ADSL over ISDN) reside in the same binder there is NEXT

Some frequencies of the downstream transmitter of an AoP line overlap with the receiver frequencies of an AoI line.


Modulation

TOC


Quadrature Amplitude Modulation (QAM)

Transmitted data = Constellation

2

3

1

0

-1

-2

-3

0,5 1 1,5 2 2,5 3

1111 1001

0000

00110111 0101 0001

0110

1110

1101 1011

1100 1000 1010

0100 0010

1001 0000 1111

Symbol length (Ts)

Symbol is represented by a variation of amplitude & phase for a particular frequencyy = A . sin (2 f.t + )

4 bits/symbol

>> QAM-16

t

A

A


QAM and Noise

Constellation

1111 1001

0000

00110111 0101 0001

0110

1110

1101 1011

1100 1000 1010

0100 0010

0

2

3

1

-1

-2

-3

0,5 1

1001

Parasite noiseSame frequency

Amplitude Phase

The Shannon-Hartley theorem : Capacity bps= 1/3 x W x SNR x G

0

2

3

1

-1

-2

-3

0,5 1

1011

Transmit Receive


QAM vs. SNR

Bits/symbolQAM Signal/Noise ratio (dB) for

BER<10-7

4 QAM-16 21,8

6 QAM-64 27,8

8 QAM-256 33,8

9 QAM-512 36,8

10 QAM-1.024 39,9

12 QAM-4.096 45,9

14 QAM-16.384 51,9

table can be used in 2 ways : (a) what is minimum required SNR to modulate N bits on a carrier(b) how many bits can be modulated given a SNR of Y dB


Discrete Multi Tone (DMT)

For ADSL, multiple carrier frequencies are modulated on the 1 ADSL line using QAM.

These frequencies are equally spaced and for each carrier the SNR is measured to determine the maximum achievable QAM.

The sum of all frequencies is put on the line

This concept is called Discrete Multi Tone (DMT)


Discrete Multi Tone example

Ts (Symbol Time)

QAM-4 f1

QAM-16 f2

QAM-4 f3

= DMT

1 DMT Symbol


DMT and ADSL

The spectrum used for ADSL is divided into 255 carriers. each carrier is situated at n x 4,3125 kHz

For the upstream direction, carriers 7 to 29 are used

For the downstream direction, carriers 38 to 255 are used

On each carrier the SNR is measured and the QAM determined. minimum : QAM-4 2 bits/symbol maximum : QAM-16384 14 bits/symbol

Symbol period for each carrier : 250 s


DMT vs. Line characteristics

7 29 38 255

4 30 125 165 1100

Frequency interference

frequency

attenuation

Bits / carrier

carrier

frequency (kHz)

ADSL filter characteristics

Line characteristics


#bits per carrier

Bits/carrier

Carriers

23456789

1011121314

Maximum value after SNR measurement per carrier at startup

Possible working value at startup

1


Bit swapping

After start-up we will use a lower QAM then possible on most of the carriers the measured SNR at startup determines the maximum possible

QAM at start-up Example : QAM-4096 corresponding with 12 bits per symbol used

QAM on that carrier : QAM-1024 (10 bits per symbol). This results in extra bits that could be allocated on that carrier

During showtime (modem operation), the SNR is measured on all carriers at regular intervals (default 1 sec) if the SNR on a certain carrier degrades resulting at a lower QAM

that can be used on that carrier, the bits of that carrier will be reallocated to other carriers where the maximum QAM is higher than the actual used QAM.

the modems will try to spread out the reallocated bits over numerous carriers.


Bitswapping explained

Bits/carrier

Carriers

23456789

1011121314

1

Sudden frequency interference decreases SNR on a number of carriers

Current max. bits/carrier

Current used bits/carrier


Bitswapping explained (2)

Bits/carrier

Carriers

23456789

1011121314

1

A lower SNR also lowers our max QAM (the number of bits on those carriers)



Affected frequencies



Bits/carrier

Carriers

23456789

1011121314

1





Bits/carrier

Carriers

23456789

1011121314

1



Noise margin is spread over the full spectrum


Communicating modems

DOWNmodulation

UPdemodulation

Unshielded Twisted Pair

DOWNdemodulation

UPmodulation

ADNT DMT FRAME (ATU-R)

2 analogue signals (UP,DOWN) travelling in opposite directions over the UTP

The ATU-R locks to the pilot carrier in the downstream direction (PLL : Phase Locked Loop)

The better the lock, the better the overall SNR !


ADSL superframe

DS 3DS 2DS 1 DS 4 DS 68DS 67. . . . . SS 69

SUPERFRAME17 ms

DMT Symbol

DMT symbol a DMT symbol is the sum of all symbols on each individual carrier

Data Symbol (DS) a data symbol is used to transmit payload information

Synchronization Symbol (SS) a synchronization symbol is transmitted after 68 data symbols to

assure synchronization and to detect possible loss of frame

ADSL symbol period Ts=17ms/69 = 246,377 s Ts=17ms/68 = 250 s (symbol period for the data plane)



TOC


Error detection and correction principle

DISTANCE = 2 t + 1

Correction Mode Detection Mode

1 bit error 2 bit error 3 bit error 1 bit error2 bit error

= Valid data

= Invalid data

• 2 bit error correction (t=2)

• 3 bit error detection (d=3)

• More than 3 bit error results in wrong correction

•5 bit error detection (d=5)



The choice of correction mode or detection mode is a consensus will you choose the ability to detect AND correct errors with the

possibility to introduce more errors OR will you choose the ability to detect a higher number of errors

with no possibility to correct them but at least you don’t introduce more errors

Some coding mechanisms will switch from correction mode to detection mode as soon as errors are detected (e.g. ATM) this is done as errors are mostly of a bursty nature and never come

alone.


Reed-Solomon correction mode

Byte1

2

3

4

239

k byte message vector

n byte code vector

254

255

240

n - k check bytes

Code RS(255,239)

Distance : n-k+1d= 255-239+1

d=17

Correction: (d-1)/2c=(17-1)/2

c = 8

With 16 check bytes, the RS code can correct up to 8 erroneous bytes

per code vector

Error correction overhead = 16/255 = 6.3 %


Reed Solomon

Message vector Ctrl

Received data

Transmitted data

Distance = 15-11+1= 5 Correction = (5-1)/2= 2

More then 2 lost bytes

Burst of errors

Data to be transmitted

Lost data


Interleaving

Message vector

Ctrl Data to be transmitted

Transmitted Data

Bloc 0 Bloc 1 Bloc 2

Received Data

CtrlCorrection CtrlCorrection CtrlCorrection CtrlCorrection CtrlCorrection

Bloc 3 Bloc 4

Bloc 0 Bloc 1 Bloc 2 Bloc 3

Burst errors

6 lost bytes

1 Byte errorper bloc!


Reed Solomon ATM burst

ATM cell: 53 Bytes

RS Decoder + Buffer

Burst of 4 ATM cells

ATM functions

Reed Solomon overhead

1B

Reed Solomon words coming from lower levels

Traffic shaper

RS has the characteristic of generating bursty ATM traffic the result might be that a policing function discards ATM cells

Therefore we need to shape the ATM traffic ATM cells will be transmitted at line rate


Delay and Interleaving depths

FAST =

NO INTERLEAVING !


Trellis coding

Trellis coding is another error detection and correction mechanism which is optional for ADSL.

Trellis principle looking at the complete data, you’re able to detect and correct

errors, similar to detection and correction is spoken language. Example :

transmitted data the water is wet and cold received data the water is llet and cold

by looking at the word “let” only, we can not decide that the sentence is wrong.

by looking at the information before and after the word (context), we can safely say that it should be “wet” instead of “let”.


ADSL & Reed Solomon

DS 3DS 2DS 1 DS 4 DS 68DS 67. . . . . SS 69

SUPERFRAME17 ms

DMT Symbol

Assume Trellis coding is NOT used !

1 data symbol corresponds to a 255 RS word. Some bytes in the RS word are framing overhead used for modem to modem communication (EOC, AOC, IB, CRC)

If RS is not used, our data still runs through the RS decoder.

The maximum downstream ADSL speed for our data : with RS (255-16-1)*8bits/byte*4000 symb/sec = 7,616 Mbps without RS (255-1)*8bits/byte*4000 symb/sec = 8,128

Mbps


Coding gain

Bits/symbol QAM uncoded Trellis RS Trellis + RS

4 QAM-16 21,5 16 17,5 12,5

6 QAM-64 27,5 22 23,5 18,5

SNR for BER = 1E-7

From the table QAM vs. SNR, we have seen that to attain a BER of 10-7 for a specific QAM you need a certain SNR. if the SNR is lower than this value, the BER will be too high. by introducing error detection and correction you lower the BER

because a number of the introduced errors will be corrected.

The mechanism introduces a coding gain resulting in an actual lower SNR that is needed to achieve a certain constellation. Trellis introduces a coding gain of approximately 5,5dB RS introduces a coding gain of approximately 4dB Trellis & RS together introduce a gain of approximately 9dB


ADSL rates

Trellis overhea

d

Attainable line rate

Reed Solomon overhead

ATM data

Framing overhead

1 up to 6 Bytes

Max. 255 Bytes

1/2bit per carrier + 4 bits

1B

ATM attainable rate maximum possible ATM rate

ATM used rate currently used ATM rate

Used line rate actual ADSL line rate

Attainable line rate maximum attainable line rate based on SNR measurements


ADSL Flavors

ADSL2 ADSL2+ READSL2


Table of contents

Overview new standards

ADSL2 Improvements

ADSL2+

READSL2 (Reach Extended ADSL2)

Multi-DSL


Overview new standards

Challenges for ADSL today


ADSL today

Reuse of existing copper wire

High Speed Data (Internet) Access

Separate network for data

Data and voice can be used simultaneously

Maximum Distance

Discrete MultiTone (DMT) modulation

Error detection/correction

Physical point-to-point connection


The Access Evolution Challenge

Tier 1: 1.5 Mb/s

Tier 3: 5.5 Mb/s

Tier 4: 7.5 Mb/s

Tier 5: 10 Mb/s

Green Zone Grey Zone Red Zone

Tier 2: 3.5 Mb/s

ADSL coverage from CO

BandwidthServices

Coverage

CO

The Access Challenge: Coverage and Bandwidth


Increasing bandwidth needs

15 MbpsTier 6

10 MbpsTier 5

7.5 MbpsTier 4

5.5 MbpsTier 3

3.5 MbpsTier 2

1.5 MbpsTier 1

Downstream BWTier

Upstream requirements could vary from 0.5 Mbps to 1.5 Mbps for symmetrical HSI

consumer services

+

++

Sample grouping of services into BW Tiers

Communication/Entertainment to N devicesVideo BroadcastInteractive video (VOD)Gaming (PC & consoles)

High Speed Internet Increased appetite for symmetrical BW

VoiceBaseband voice

Residential

35-45Incre

ase

d

AR

PU

>100

Communication/Entertainment to N devicesVideo broadcast, Interactive video

Access servicesCorporate leased line, access, business access

VoiceBaseband voice, VoDSL

Business


Coverage

VDSL

ADSL2(plus)ADSL

ADSL2READSL2


Higher coverage needs: extending the reach

6 Mb/sRemote DSLAM

Remote DSLAM

Remote DSLAMCentral

Office


DSL standards evolution to meet the challenges

ADSLADSLADSLADSL

ADSL2plus

Downstream bandwidth boost up to 24 Mb/s

Reach Extended DSL (READSL2)

Loop reach increase of 600-900m up to 6 km(192 Kb/s DS – 96 Kb/s US)(0.4 mm loop)

Next generation ADSL= ADSL2

•10% improved performance on longer loops

•Improved OAM

VDSLVDSLVDSLVDSL

Different bandplans

•Plan 997 : compromise bandplan for symmetric and asymmetric traffic

•Plan 998 : optimized for asymmetry

•Bandwidths available up to 55 Mb/s on short loops


ADSL restrictions

Unable to provide consistent performance over longer distances.

Several potential improvements defined in the last years:

Data rate versus loop reach performance Loop diagnostics Deployment from remote cabinets Spectrum control Power control Robustness against loop impairments and RFI, operations

and maintenance.After 3 years of field expierence with ADSL, the next steps are ADSL2,

ADSL2+ and READSL2


Overview of the new standards

• G.dmt = G.992.1 = ADSL• G.dmt.bis = G.992.3 = ADSL2

– Main improvements:– performance: raising the bar;– loop diagnostics tools; – improved initialization & fast start-up ;– power management;

• G.adslplus = G.992.5 = ADSL2+

– ADSL2+ is defined as delta to ADSL2– Downstream bandwidth increase

(frequency spectrum up until 2.2 MHz)– At least 16 Mbit/s should be supported (up to 24

Mbit/s)

• READSL =Annex L G.992.3– Reach Extended ADSL2– Targets 192 kbit/s DS – 96 kbit/s US on 6km

0.4mm loops

G.dmt = G.992.1 = current ADSL

G.dmt.bis = G.992.3 = second generation ADSL2

G.adslplus = on G.992.3 = ADSL2+

ITU-T

READSL= G.992.3 annex L = Reach Extended DSL


ADSL standards overview


Some examples of ‘new’ annexes: Annex I, J and M

3kHz 138kHz

13.3 dBm upstream

UP

1,1MHz

19.9 dBmdownstream

DOWN G.992.3 Annex I

276kHz

13.4 dBm upstream

UP

1,1MHz

19.3 dBmdownstream

DOWN G.992.3 Annex J

254kHz3kHz

276kHz

UP

1.1 MHz

DOWN G.992.3 Annex MP

OT

S


ADSL2 IMPROVEMENTS

G.992.3


Improvements in area’s

Real world: Bridged taps, Crosstalk & Narrowband Interferers

Ease of CPE installation

Enabling applications:voice, games and video

The green line:Power savings

Adaptation to time varying line conditions

Enabling implementation technologies

ADSL Anywhere: RU deployment

Monitoring and trouble resolution tools

All Digital Mode

Egress Friendliness

Multi-vendor Interoperability

After 3 years of field experience …


ADSL2 mayor improvements

Performance: raising the bar Improved modulation and coding gain

Power management

Improved initialization

Fast start-up

Loop diagnostics

On-Line configuration

All digital mode ADSL

Framing

Improved application support

Home installation


Differences in ADSL and ADSL2 datarates

Standard mandatory and upperlimit downstream datarates.

RecommendationMandatory downstream datarate

Standard architecture upper limit downstream datarate

ADSL (G.992.1) 6.144 Mbps8 Mbps (15Mbps for optional S=1/2)

ADSL2 (G.992.3)

8 Mbps 15 Mbps

Standard mandatory and upperlimit upstream datarates.

RecommendationMandatory upstream datarate

Standard architecture upper limit upstream datarate

ADSL (G.992.1) 640 Kbps 1.5 Mbps

ADSL2 (G.992.3)

800 Kbps 1.5 Mbps


Performance difference between ADSL and ADSL2

data rate increase of about 50-80 kbps reach increase of 250 Ft 26 AWG loop3000

0

500

1000

1500

2000

2500

14 15 16 17 18

26 AWG loop (Kfeet)

bit

rate

(kb

ps)

ADSL downstream

ADSL2 downstream

ADSL upstream

ADSL2 upstream

Noise condition IC2:

At CO side:

12 Self Xtlk, 12 G992.1

ADSL

and -140dBm/Hz white

noise

At CPE side:

6 Self Xtlk, 6 G992.1 ADSL

and -140dBm/Hz white

noise


Performance : raising the bar

Better modulation efficiency by mandatory trellis-coding. Was optional for ADSL (G.992.1).

The 1-bit QAM constellation provide higher data rates on long lines where the SNR is low.

Receiver determined tone reordening is a better defence against AM radio interference. Spread out non stationary noise due to AM RFI to get better coding gain from

Viterbi decoder

Improved performance by allowing data modulation on the pilot tone.

Mandatory support of DSL Forum TR-048 for North-America (annex A) ETSI TS 101 388 V1.3.1 for Europe (annex A&B)


Reduced framing overhead/Optimal RS coding gain

In ADSL (G.992.1) the overhead bits per frame are fixed and consume 32Kbps of

the payload data. By a low data rate of 128Kbps (on long lines), this is 25%

overhead.

In ADSL2 the overhead bits can be programmed from 4 to 64Kbps. This

provides an additional 28Kbps for payload data.

Through improved flexibility and programmability in the construction of the RS

codewords, ADSL2 achieves higher gain from the RS code when the data rates

are low on long lines.

Support of up to 4 frame bearers and 4 latency paths.


Improved Initialization

Receiver gives feedback to the CO.

Pilot tone is allocated by receiver

Arbitrary allocation (by receiver) of carriers used for initialization messages.

Tone blackout (disabling tones) to enable RFI cancellation schemes.

ATU-R chooses configuration taken into account the constraints given by the CO (improved rate

adaptivity concept).

Receiver and transmitter determine duration of init signals

Power cutback possible at both ends


Power Management (Power consumption)

ADSL: always in full-power mode

ADSL2: three power modes: L0 full power mode: showtime (high data traffic) L2 low-power mode: keep alive mode (background traffic) L3 low-power mode: sleep mode (user is off-line)


Power Management diagram

Normal operation

“keep alive”

Sleep


Loop Diagnostics Tools to determine field problems

ADSL

trouble-shooting during and after installation and performance monitoring was a challenging obstacle in the service deployment.

To tackle problem, ADSL2 transceivers are enhanced with extensive diagnostic capabilities:

Collecting measurements at the beginning of showtime.

This mode is comparable with the existing Alcatel Golden ATU functionality.

In-service (showtime) monitoring capabilities

providing information on line quality and noise conditions at both ends of the line: signal attenuation, SNR margin, attainable net data rate, SNR in function of frequency… Most of these capabilities are comparable with the existing Alcatel Golden ATU functionality.


Loop Diagnostics Tools to determine field problems

Special non-showtime diagnostic-testing mode

Collecting measurements

even when line quality is too poor to actually get into showtime. This mode can be entered under operator control.

The following test parameters can be measured and passed to the near‑end management entity:

Channel Characteristics Function H(f) per subcarrier (CCF-ps); Quiet Line Noise PSD QLN(f) per subcarrier (QLN-ps); Signal-to-Noise Ratio SNR(f) per subcarrier (SNR-ps); Line Attenuation (LATN); Signal Attenuation (SATN); Signal-to-Noise Margin (SNRM); Attainable Net Data Rate (ATTNDR); Near‑End Actual Aggregate Transmit Power (ACTATP); Far-end Actual Aggregate Transmit Power (ACTATP);


On-Line Reconfiguration (OLR)

Reconfiguration without interruption of service and without errors. “Bit Swapping” (BS): data rates are kept

“Dynamic Rate Repartitioning” (DRR): data rates are repartitioned among different latency paths

“Seamless Rate Adaptation” (SRA):total data rate is changed


Bit swapping explained (1)

Bits/carrier

Carriers

23456789

1011121314

1

A lower SNR also lowers our max QAM (the number of bits on those carriers)



Affected frequencies


Bit swapping explained (2)

Bits/carrier

Carriers

23456789

1011121314

1




Seamless Rate Adaptation (SRA) - details

ADSL: re-initialization.ADSL2: adapting the data rate in real time.

ADSL ADSL2

Modem reset Initialization of 10 sec

Reduced rateforever

time time

Kbps Kbps

SRA

SRA

Radiointerference

Radiointerference

Radiointerference

Reducedrate

Back to original rate

Radiointerference


Fast Start-up

Reduce the initialization time from 10 s to 3 s.

Allow ATU’s to quickly enter Showtime: From a L3 power management state In case of error during Showtime

Data Rate fine tuning in Showtime. Seamless Rate Adaptation (SRA) should be implemented


All Digital Mode ADSL (no underlying service)

All Digital Loop: extend the upstream bandwidth. ADSL2 Annex I:

Upstream tones 1-31 instead of 6-31 for ADSL over POTSe.g. 100 kbps extra upstream

ADSL2 Annex J: Upstream tones 1-63 instead of 28-63 for ADSL over ISDNe.g. 750 kbps extra upstream

UP DOWN

UP DOWN

POTS/ISDN


Channelization and Voice over DSL

Split the bandwidth into different channels with different link characteristics for different applications. ADSL2 simultaneous support: Voice application with low latency but higher BER. Data application with high latency but low BER.

Channelized Voice-over-DSL (CVoDSL): transport of voice directly over DSL. No transport of voice into higher layer protocols such as ATM or IP

but directly onto DSL (DMT symbols).


Channelized Voice over DSL

“Normal” VoDSL


Bandwidth efficiency comparison

VeDSL = CVoDSL


ADSL2: frame bearers and latency paths

A specific frame bearer is connected to only one latency path Frame bearer could be any data: ATM, voice, … Every latency path could have different characteristics

SCRAMBLER

RSFEC

INTERLEAVER

MU

LT

IPL

EX

ER

RS Coding Info

Interleaving depth

Latency path #0

Fra

me b

eare

rs

LA

TE

NC

Y P

AT

HM

UL

TIP

LE

XE

R

PM

Latency path #p

#0

#n

…

…

n= 0 .. 3P= 0 .. 3


IMA bonding for higher data rates

Higher data rates by bonding two or more copper pairs together

Bonding mechanism: IMA (inverse multiplexing for ATM).

ADSL2

ADSL 1

ADSL x

……

AT

M I

MA

ATM


Inverse Multiplexing over ATM (IMA)

IMA : ATM stream is transported on a number of lower-rate physical links

... ...

IMA GroupPhysical

links

1

2

3

1

2

3

IMA control protocol cells (ICP)

Single ATM cell streamfrom ATM layer Original ATM cell stream

to ATM layer

TX RXIMA virtual link


Downstream rate for bonding 2 lines


ADSL2+

G.992.5


ADSL2+ doubles the frequency spectrum


ADSL2+ characteristics

ADSL2+ : downstream frequencies up to 2.2 MHz (512 carriers)

Increased downstream data rates on shorter lines (in Mbps):

Improved spectral compatibility between CO and remote cabinet

3.55.95.53.0 km

1.03.03.04.0 km

01.01.05.0 km

7.2106.22.0 km

10.0137.41.0 km

12.014.580.5 km

remote ADSL2+

ADSL2+ADSLdistance


ADSL2+ doubles the max. data rate


Overview of downstream data rates (ADSL2+ added)

Recommendation

Mandatory downstream datarate

Standard architecture upper limit downstream datarate

ADSL (G.992.1) 6.144 Mbps8 Mbps (15Mbps for optional S=1/2)

ADSL2 (G.992.3) 8 Mbps 15 Mbps

ADSL2+ (G.992.5)

16 Mbps 24,5 Mbps


ADSL2+ used to improve spectral compatibility


Reach Extended ADSL2 (READSL2)

G.992.3 Annex L


Reach Extended ADSL2 concept

On long loops (e.g. up to 18 kft 26 AWG)

Increase in reach of 1 to 2 kft (300-600m) (26 AWG, 0.4mm loop)

New ADSL2 PSD mask with reduced crosstalk to existing services. Leads to a small reach increase on the longest loop of about 0,5

kft relative to ADSL2, if SHDSL is a dominating upstream killer. In self-crosstalk the length increases up to 2kft - 600m.

Longer reach achieved by using a higher power level (PSD) in a smaller band (same or even less total Tx power)


READSL2 PSD masks

Mandatory non-overlapped downstream PSD mask

Upstream PSD masknumber 1


Reach Improvement by READSL2Performance ADSL and READSL

0

500

1000

1500

2000

2500

14 15 16 17 18

Kfeet 26 AWG loop

bit

rate

(kb

ps)

ADSL US

READSL US

READSL DS

ADSL DS

=±4,3km =±5,2km =±5,5km

12 self crosstalkers with –140dBm/Hz white noise at CO side;

6 self crosstalkers with –140dBm/Hz white noise at CPE side.


Reach for ADSL vs. READSL2

Service ADSL READSL2

800 Kbps DS / 96 Kbps US 16 Kft (4,9 km) 18 Kft (5.5 km)

400 Kbps DS / 96 Kbps US 17 Kft (5,2 km) > 18 Kft (5.5 km)


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