DSL2-1

DSLPhysical Layer

Prepared by:peter.macaulay@ZDSL.com

© 2005 by ZDSL.comADSL, HDSL, IDSL, SDSL, VDSL = xDSL

DSL2-2

ADSL

• Asymmetric Digital Subscriber Line• ANSI T1.413-1998• G.992.1 = G.dmt = 8.1/0.8 Mbps (256 bins)• G.992.2 = G.lite = 1.5/0.5 Mbps (128 bins)• G.992.1 with S=1/2 line coding yielding 12 Mbps • G.992.3 = G.dmt.bis (July2002) aka ADSL2 (256 bins)• G.992.3 Annex L = Reach Extended RE-ADSL2• G.992.4 = G.lite.bis• G.992.5 = ADSL2+ = 24 Mbps at 5,000 feet (512 bins) • G.993.2 = VDSL2 = 100 Mbps (May 2005)

ITU-T UpdatesG.992.3 = ADSL2G.992.5 = ADSL2+

DSL2-3

DMT ADSL

• 4kHz low pass filter (LPF) for voice• sub-carrier spacing for discrete multitones (DMT)

Pilot Tone #64 = 276kHz

DSL2-4

DMT Operation

DMT - Discrete Multi-Tone ModulationOrthogonal Sub-channels Spaced @ 4.3125 kHz

SNR (Signal to Noise Ratio) Marginsignal above the background noise floor (i.e. +8dB)

QAM Modulated With 2 - 14 BitsNote:

22 = 4 Constellation Points214 = 16,384 Constellation Points

64-QAM 4-QAM

frequency

Ene

rgy

/ ton

e

frequency

upstream

POTS

pow erspectrum

4 kHz 2.2. MHz

dow nstream

1.1 MHz

DSL2-5

Three Down Stream (DS) Speeds

1. Theory– Possible 256 bins, 12 Mbps max

2. Actual– Actual for the copper local access loop – Perhaps 188 bins, 9.6 Mbps max– Some bins disabled by the copper loop– Will depend upon “bits-per-bin” loading

3. Tariff– The service you requested, purchased– Perhaps 140 bins, 1.5 Mbps max or less bits-per-bin– Some bins disabled by the service provider

DSL2-6

Quad Spectrum Proposal• Extend the DS (Downstream) bins to 3.75 MHz• Widen the US (Upstream) from 138kHz to 276 kHz• Enhance the bit loading beyond 15 bits per bin

26kHz 138kHz 2.2MHz1.1MHz 3.75MHz

ADSL1ADSL2+

VDSL2

US DS

Bins

6-31

Bins

… 256

Bins

… 512

Bins

… 870

DSL2-7

Bits Per Tone (Annex A: Upstream)• Bits per tone• Bits per bin

• POTS=1-5• Annex A• US=6-31

• Note:• Tone 10 =

– 11 bits – 10*4.3125

(43.125kHz)

Upstream Bits Per Tone

02468

10121416

1 6 11 16 21 26 31 36 41 46 51 56 61

Tone Number

Bits

Per

Ton

e

DSL2-8

Bits per Tone (Downstream 32-256)

ADSL2

. . .

15

15

15

14

13

13

13

13

11

11

109977553000

198.375194.062189.750185.437181.125176.812172.500168.187163.875159.562155.250150.937

…kHz

……114611451044943942741740539538337036035……

BitsTone

kHz = tone number x 4.3125

Tone

Tone # 46@ 198.375 kHz

= 11 bits

DSL2-9

Bits per Tone (Downstream 32-256)

• ADSL2

• . . .

1104.001099.6871095.3751091.0621086.7501082.4371078.1251073.812

…1052.2501047.9371043.6251039.312

…kHz

1525614255142541425315252152511525015249……15244152432242

15241……

BitsTone

ADSL2Tone 256@ 1.1MHz= 15 bits

Tone242

Ouch!

DSL2-10

Bit Swap• If the SNR changes for one tone, the bit swap

protocol re-deploys the allocation of bits among the sub-carrier tones with no retrain of the modems or change in the net data rates.

• Bit swap only works for an equal number of bit (+/-)• For testing a tone in the range 70-100 is selected• Tone power is increased to –75dBm power • Tone power in then increased by 5dBm until a bit

swap occurs while recording the bits per tone map• Reference: DSL Forum TR-067 “ADSL Interoperability

Test Plan”

DSL2-11

Seamless Rate Adaptation (SRA)

• SRA was introduced with ADSL2 and is included in ADSL2+

• SRA dynamically re-assign bits per tone with no modem retrain

• DSL Forum WT-100 “ADSL2/ADSL2plus Interoperability Test Plan” may add this test

DSL2-12

G.992.5 Upstream PSD (ADSL2+)

PSD indBm/Hz

21.5 dB/octave

–97.5 peak+15 dBrn0-4 kHz

–34.5 dBm/Hz peak PSD

-72 dB/octave–100 dBm/Hz peak PSD

in 10 kHz window

peak PSDin 1 MHz windowabove 3750 kHz

0 4 25.875 138 686 12000 Frequencyin kHz52751411 1630

-15 dB/dec

–92.5 dBm/Hz

-93.2 dBm/Hz

–110 dBm/Hz –112 dBm/Hz–100 dBm/Hz

243

Passband 26 – 138 kHzPOTS

Power Spectral Density (PSD)

DSL2-13

G.992.5 Downstream PSD (ADSL2+)• G.992.5

PSD indBm/Hz

36 dB/octave

–97.5 peak+15 dBrn0-4 kHz

–36.5 dBm/Hz peak PSD

–65 dB/octave–100 dBm/Hz peak PSD

in 10 kHz window

peak PSDin 1 MHz windowabove 3750 kHz

0 4 138 1104 2208 12000 Frequencyin kHz

31751622 3001.5

250072253750 4545

–18 dB/octave–3 dB/octave

–78 dB/octave–46.5 dBm/Hz

–47.8 dBm/Hz

–59.4 dBm/Hz

–80 dBm/Hz

–110 dBm/Hz –112 dBm/Hz–100 dBm/Hz

80

–92.5 dBm/Hz

–72.5 dBm/Hz

–44.2 dBm/Hz

4.63 dB/octave

Passband 138 – 2208 kHz

DSL2-14

ANSI and ITU (G.dmt)• ANSI T1.413 - 1998• ITU-T G.992.1-1999 = ADSL (ADSL1)• ITU-T G.992.3-2002 = ADSL2 (July 2002)• ITU-T ADSL includes localization for different countries;

– Annex A with POTS– Annex B with ISDN– Annex C with TCM-ISDN for Japan– Annex H for Japan

• G.992.1 has an enhanced activation compared to ANSI called G.994.1 (G.hs – handshake). Instead of a single tone being used to indicate optional features supported by a DSL modem, several tones digitally transmit the same information for a more robust startup.

• G.997.1 (G.ploam) -- management

DSL2-15

G.992.3 (G.dmt.bis) = ADSL2

• ITU-T Study Group 15, Question 4 (SG15-Q4)• May 2002 consent, July 2002 approved• Technical freeze on ADSL• “.bis” means “other” or second version• Major changes in ADSL2 …

– Improved bit rate in the downstream– Mandatory Trellis Code– Line Diagnostics– Reduced Power– All Digital Mode

DSL2-16

G.992.3 (ADSL2) - Bonding• ADSL2 provides support for inverse multiplexing• Bonding of multiple copper pairs for transport of a• Single ATM stream (ATM Forum Standard af.phy-

0086.001 Inverse Multiplexing for ATM (IMA), Version 1.1)

32 Mbps on 4 bonded pairs24 Mbps on 3 bonded pairs16 Mbps on 2 bonded pairs

DSL2-17

G.992.3 (ADSL2) – Bonding Rates

Diagram source:www.aware.com

DSL2-18

G.992.3 (ADSL2) – Speed Change• Improved bit rate

– Was 2-15 bits, now also 1-bit signal constellations– four-dimensional, 16-state trellis-coded and 1-bit

quadrature amplitude modulation (QAM) constellations – Results in a 96-192 kbps greater downstream

• Reduced framing overhead for faster transfers• Adaptable pilot tone location (carrier #64 = 276kHz)

– Will result in better clocking• Mandatory Trellis coding and Reed Solomon RS=15• Explicit rate negotiation

– Will be good for multi-vendor configurations– Better tone reordering for RFI robustness

DSL2-19

G.992.3 (ADSL2) – Rate & Reach

Diagram source:www.aware.com

21.5 kft =6.5 km

DSL2-20

G.992.3 (ADSL2) – SRA• ADSL2 can dynamically adapt to changes in line

conditions:– Crosstalk from other DSL in the same cable– Narrow band AM (radio) disturbers– Temperature changes– Water in the cable bundle

• Uses online reconfiguration (OLR) when SNR changes• SRA is important for video to avoid tiling (pixelization)• Seamless rate adaptation (SRA) enables the transceiver

to monitor line conditions and dynamically adapt the data rate “seamlessly”, i.e. without bit errors or requiring a service interruption for retraining

DSL2-21

G.992.3 (ADSL2) - Digital Mode• All digital mode (no POTS, could have derived voice)• About 256 kbps additional up stream data rate• 0-26 kHz used for digital transmission not voice• This option is not suitable for line sharing

DSL2-22

G.992.3 (ADSL2) Line DiagnosticsChanges:• Line diagnostics and background noise measurement• Provides information when line quality is too poor to link• Measure of line noise, loss, SNR• Built-in to the DSLAM and CPE• Includes standard messages to the operator

Benefit:• Will result in less technicians to the field (less truck rolls)• Will be helpful in troubleshooting RFI and bridged taps

DSL2-23

ADSL2 DELT• DELT (Dual-Ended Line Test)• Defined by the ADSL2 (G.992.3) • Enables the measurement of line conditions at both

ends without dispatching maintenance technicians to attach test equipment to the end of the line.

• The information helps to isolate the location and the sources of impairments caused by crosstalk, radio-frequency interference and bridge taps.

• Data Collection is "DELT physical-layer technology”• Data Processing is "Loop Identification”• SELT (Single-Ended Line Test) future option

DSL2-24

SELT/DELT Comparison

DSL2-25

G.992.3 (ADSL2) – Low Power

• L0 is ADSL2 full power mode• L2 is low power mode at the ATU-C (DSLAM) while

idle will result in better power especially for remote DLC (Digital Loop Carrier) configurations

• L3 is low power mode at the ATU-R (user) and ATU-C enables the modem to sleep when information is not being transmitted (e.g. overnight) – it takes 3 seconds to come out of L3 (sleep mode)

• Ability to disable tones to aid spectral compatibility• Extended training intervals• Power back off during startup

DSL2-26

SNR MarginCapacity per tone depends On SNR

– About 3 dB SNR difference per modulation bit– Coding Gain, Noise Margin, Timing Accuracy– BER 10-7– There is a direct correlation of the SNR Margin and

the modulation bits per tone in each sub-channel

Total Rate = Sum of Bits-per-Bins x 4,000

DSL2-27

Power Cut Back

• Reduces dynamic range required by Modem• Reduces overall cable plant crosstalk level but reduces data rate• DSLAM measures US power on bins 7 – 18• DSLAM applies a 0 – 12 dB reduction to Downstream power

Power Cut Back

0

2

4

6

8

10

12

14

025

050

075

010

0012

5015

0017

5020

0022

50

Distance 26 awg [feet]

Pow

er C

ut B

ack

[dB

]

Measured Power CutBackPredicted Cutback for26 AWG cable

DSL2-28

Fast Path versus Interleaved Path• Dual paths exist within the ADSL standard

DSL2-29

Interleave Depth• The interleave depth is defined by the S and D

parameters or the Impulse Noise Protection (INP)• INP = 0 (none), ½, 1, 2, 4, 8, 16• S = 1,2,4,8,16 D = 1,2,4,8,16,32,64• Interleave delay can be from 4.25 to 263.75 msec

DSL2-30

Interleave• S: Interleave DMT symbols per FEC (forward error

correction) Reed Solomon (RS) code word– S = 1, 2, 4, 8, 16

• D: Interleave depth– D = 1, 2, 4, 8

DSL2-31

Superframe

DSL2-32

G.992.3 (ADSL2) – Ethernet• ADSL2 includes a packet mode transmission

convergence layer (PTM-TC) that enables connection of ADSL2 modems to packet services (Ethernet)

• Extensive configuration capability for PTM-TC with configuration of …– latency– bit error rate– minimum/maximum data rate to meet packet

protocol requirements

DSL2-33

Reach-Extended ADSL

• G.992.3 Annex L• Approved November 2003

• RE-ADSL2 performance improvements result from new power spectral density (PSD) masks designed to improve data rates on extra-long phone lines

• For downstream data rate of 384 kbps, results in 20%• RE-ADSL2 is expected to operate as an alternative

mode of an ADSL2 or ADSL2+ chipset that a carrier can choose to activate for particular customers

DSL2-34

RE-ADSL2 (Down Stream Rate)• ADSL 2 Annex L • 256 bins• 500 kbps at 18,500’• 18,500’ = 5.6 km• 384 kbps at 28,000’• 28,000’ = 8.5 km

• RE is adding ½ km• 1,500’ = 0.460 km• 26 AWG• 12 other ADSL

DSL2-35

G.992.5 (ADSL2+)• January 2003 approved (512 bins up to 2.2 MHz)• 24 Mbps @ 3kft (0.9km), 16 Mbps @ 6kft (1.8km)• >8kft (2.4km) ADSL1, ADSL2, ADSL2+ similar

DSL2-36

G.992.5 (ADSL2+)• Possible to reduce cross talk by using different bins for

different users• Possible to mix ADSL2 (1.1 MHz) with ADSL2+ (2.2 MHz)

DSL2-37

Annex Summary

N/ADOWNDOWNUPUP-I (Japan ADSL2)

DOWNDOWNUPUPPOTSPOTSM (ADSL2+)More Upstream

N/ADOWNDOWNUPPOTSPOTSL (RE-ADSL2)

DOWNDOWNUPUPUP -J (All Digital)

DOWNDOWNDOWNUPUP-I (Japan ADSL2+)

DOWNDOWNDOWNUPPOTSTCM-ISDN

I (Japan ADSL)

N/ADOWNDOWNUPPOTSTCM-ISDN

C (Japan)

DOWNDOWNUPISDNISDNISDNB (Germany)

DOWNDOWNDOWNUPPOTSPOTSA (NA, EU, Asia)

#256 - 512=1.104 to2.208 MHz

#65 - 255=280.3

kHz

#32 - 64=138.0

kHz

#6 - 31=25.875

kHz

#1 - 5 Bins=0 Hz

TYPEANNEX

DSL2-38

Automode

1. ADSL2 would connect at 690 kbps for CPE at 18,000 feet (4.5 km). Instead …

2. ADSL2/ADSL2+ CO collects loop data during initialization and training

3. Automode determines RE-ADSL2 is the best configuration based on line conditions

4. DSLAM configures customers port for RE-ADSL2 mode5. CPE line at 1.1 Mbps (a 160% improvement over

ADSL1)

CO DSLAM CPELoop

DSL2-39

Summary of Rate/Reach

2.4 km8 kft

4.3 km14 kft

3.0 km10 kft

VDSL2 100Mbps

DSL2-40

DSM (Dynamic Spectrum Mgmt)

• DSM level 0– No coordination

• DSM level 1– Distributed multi-user power allocation– Implementation of Iterative Water Filling (IWF)

• DSM Level 2– Centralized multi-user power allocation– Optimal Spectrum Management (OSM)

• DSL Level 3– Multi-user detection – Also called vectoring

DSL2-41

ADSL Line Repeaters• Telrad DataRacer

– ARU (ADSL Repeater Unit) 2-wire with data + voice• Symmetricom GoLong

– Mid-span ADSL repeater (data only, no voice )– 1.5Mbps/128kbps down/up to 30,000 feet (9100 m)

DSL2-42

SHDSL• Single-Pair High-bit-rate DSL (SHDSL)• 16 level TC-PAM line coding• Trellis Coded Pulse Amplitude Modulation (TC-PAM)• ITU G.991.2 approved April 2001 (was G.shdsl)

– 2-wire (2.36/2.36) … 192 kbps steps– 4-wire (4.7/4.7) … 384 kbps steps

• STU-R connects to STU-C • Very good spectral compatibility with other services• Some vendors are providing SHDSL over POTS

DSL2-43

GoDigital (Pole Mounted RT x8)• Pole mounted• Single pair serves x8 CPE

• 24,000’ @ 24 AWG– 7.3km

• 32,000’ @ 22 AWG– 9.8km

• Optional midspan pole RT– 38,000’ @ 24 AWG– 11.6km

DSL2-44

VDSL2• Very-High-Data-Rate Digital Subscriber Line• ITU-T G.993.2• Downstream rates:

– 12.96 Mbps (4,500 ft.– 1500m)– 25.82 Mbps (3,000 ft.– 1000m) = FTTN (Fiber-to-the-Node)– 51.84 Mbps (1,000 ft. – 300m) = FTTC (Fiber-to-the-Curb)– 100 Mbps (300 ft. – 100m)

• Upstream rates from 1.6 to 2.3 Mbps• Symmetric rate (13 Mbps) possible• Simpler than ADSL

– Shorter lines, fewer transmission constraints– Ten times faster

• Enables multiple video streams• HDTV compatible (19 Mbps or 10 Mbps compressed)

DSL2-45

VDSL2 Frequency Plan (NA)

• North American Band Plan

• 0-US0: Upstream start f0L = 4 kHz or 26 kHz• 0-US0: Upstream end f0H = 138 kHz or 276 kHz• 1-DS1: Downstream 138 kHz –3.75 MHz• 1-US1: Upstream 3.75 MHz – 5.8 MHz• 2-DS2: Downstream 5.8 MHz – 8.5 MHz• 2-US2: Upstream 8.5MHz –12.0 MHz

DSL2-46

VTU-R Transmit (Upstream) North America (NA)

25 kHz <PSD1> 138-276 kHz

DSL2-47

VTU-O Transmit PSD (Downstream) NA

30000

DSL2-48

VDSL2 Frequency Plan (Europe)

DSL2-49

VDSL Spectrum

• Frequency Plan 998

138kHz 3.75MHz 5.2MHz 8.5MHz 12MHz

DSL2-50

VDSL2 Proposed Rate/Reach• rate

2200 ft = 670m

DSL2-51

DSL ConfigurationDesign note;1) DSLAMs can support multiple DSL line cards (xTU-C)

– For example;– DSLAM with G.dmt, G.shdsl, G.vdsl– CPE can then choose speed/service required– Future cross connects at the DSLAM could provide

for customer speed/service increases2) DSLAMs could be integrated with the POTS line card to

provide POTS -or- DSL options to all telephone subscribers– this will benefit facilities based exchange carriers

DSL2-52

DSL Deployment Model

1. ILEC/CLEC sends CPE to customer for self install2. ILEC/CLEC drives to customer site for the install3. Retail: Customer buys the DSL CPE in a store

(Radio Shack, Fry’s,…), customer does self install,ILEC/CLEC activates the DSL line (connects the DSLAM)

DSL2-53

DSL Flavors• ADSL = ITU-T G.dmt = G.992.1 (world standard)• SHDSL = ITU-T G.shdsl = G.991.2 (world standard, business focus)• VDSL = Standards track with ETSI/ANSI

• IDSL = longest reach (part of DSL Anywhere)• SDSL = multirate DSL (business focus)• HDSL = T1 4-wire (most popular DSL to date)• HDSL2 = T1 2-wire

• MVL = Paradyne proprietary, long reach• RADSL = Globespan proprietary (voice, data, video)• 1-Meg = Nortel proprietary

• xDSL = any of the above• YDSL = CATV solution (“why” DSL?)

DSL2-54

EFM

• Ethernet in the First Mile (EFM)• IEEE P802.3ah, copper track• 10 Mbps for 750m

– Ethernet over VDSL– Dual mode, EoVDSL + 100Base-Cu

• http://www.efmalliance.org/• www.t1.org for T1E1.4 Working Group

DSL2-55

PON (Passive Optical Network)• APON

– Asynchronous Transfer Mode (ATM) PON • EPON

– Ethernet PON• BPON

– Broadband PON– Combination of Passive Optical Networking (PON)

and Wavelength Division Multiplexing (WDM)• GPON

– Gigabit Capable PON– ITU-T G.gpon.gsr

DSL2-56

• blank

DSL2-57