Prepared by: peter.macaulay@ZDSL.com

1. DSL
Physical Layer
Prepared by:
peter.macaulay@ZDSL.com
© 2005 by ZDSL.com
ADSL, HDSL, IDSL, SDSL, VDSL = xDSL
DSL2-1
ITU-T Updates
G.992.3 = ADSL2
ADSL G.992.5 = ADSL2+
• 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)
DSL2-2

2. DMT ADSL
• 4kHz low pass filter (LPF) for voice
• sub-carrier spacing for discrete multitones (DMT)
Pilot Tone #64 = 276kHz DSL2-3
p ow er
spe ctrum
upstrea m
dow nstream
DMT Operation PO T S
4 kHz 1.1 MHz 2.2 MHz
. frequency
Energy / tone
DMT - Discrete Multi-Tone Modulation
Orthogonal Sub-channels Spaced
@ 4.3125 kHz
frequency
SNR (Signal to Noise Ratio) Margin
signal above the background
noise floor (i.e. +8dB)
QAM Modulated With 2 - 14 Bits
Note: 64-QAM 4-QAM
22 = 4 Constellation Points
214 = 16,384 Constellation Points
DSL2-4

3. 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
DSL2-5
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
VDSL2
ADSL2+
ADSL1
US DS
Bins Bins Bins Bins
6-31 … 256 … 512 … 870
26kHz 138kHz 1.1MHz 2.2MHz 3.75MHz
DSL2-6

4. Bits Per Tone (Annex A: Upstream)
• Bits per tone Upstream Bits Per Tone
• Bits per bin
16
14
• POTS=1-5 12
Bits Per Tone
• Annex A 10
8
• US=6-31 6
4
• Note: 2
0
• Tone 10 = 1 6 11 16 21 26 31 36 41 46 51 56 61
– 11 bits Tone Number
– 10*4.3125
(43.125kHz)
DSL2-7
Bits per Tone (Downstream 32-256)
Tone kHz Bits
… ADSL2
… …
35 150.937 0
36 155.250 0
37 159.562 3
38 163.875 5 Tone # 46
1 1 1 1 1 1 1 1 1 1 1
39 168.187 5 @ 198.375 1kHz
0 0 0 3 5 5 7 7 9 9 0 1 3 3 3 3 4 5 5 5
40 172.500 7 = 11 bits
41 176.812 7
42 181.125 9
43 185.437 9
44 189.750 10 ...
45 194.062 11
46 198.375 11
Tone
… … DSL2-8
kHz = tone number x 4.3125

5. Bits per Tone (Downstream 32-256)
Tone kHz Bits Tone
242
• … ADSL2 … …
Ouch!
241 1039.312 15
242 1043.625 2
243 1047.937 15
244 1052.250 15
… … …
249 1073.812 15
250 1078.125 15 ADSL2
251 1082.437 15 Tone 256
252 1086.750 15 @ 1.1MHz
253 1091.062 14
= 15 bits
• 254 1095.375 14 ...
255 1099.687 14
DSL2-9
256 1104.00 15
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”
DSL2-10

6. 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
DSL2-11
G.992.5 Upstream PSD (ADSL2+)
Power Spectral Density (PSD)
PSDin
dBm/Hz –34.5 dBm/Hz peak PSD
-72 dB/octave
21.5 dB/octave
–100 dBm/Hz peak PSD
in 10 kHz window
–97.5 peak -15 dB/dec peak PSD
+15 dBrn in 1 MHz window
0-4 kHz above 3750 kHz
-93.2 dBm/Hz
–92.5 dBm/Hz
–100 dBm/Hz –110 dBm/Hz –112 dBm/Hz
Frequency
0 4 25.875 138 243 686 1411 1630 5275 12000
in kHz
Passband 26 – 138 kHz DSL2-12
POTS

7. G.992.5 Downstream PSD (ADSL2+)
• G.992.5
PSD in –18 dB/octave
dBm/Hz –36.5 dBm/Hz peak PSD –3 dB/octave
36 dB/octave –65 dB/octave
–100 dBm/Hz peak PSD
4.63 dB/octave –78 dB/octave
in 10 kHz window
–46.5 dBm/Hz
–97.5 peak peak PSD
–47.8 dBm/Hz in 1 MHz window
+15 dBrn
–44.2 dBm/Hz above 3750 kHz
0-4 kHz
–72.5 dBm/Hz –59.4 dBm/Hz
–92.5 dBm/Hz –80 dBm/Hz
–100 dBm/Hz –110 dBm/Hz –112 dBm/Hz
Frequency
0 4 80 138 1104 1622 2208 3001.5 3750 4545 7225 12000
in kHz
2500 3175
Passband 138 – 2208 kHz DSL2-13
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
DSL2-14

8. 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
DSL2-15
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 pairs
24 Mbps on 3 bonded pairs
16 Mbps on 2 bonded pairs
DSL2-16

9. G.992.3 (ADSL2) – Bonding Rates
Diagram source:
www.aware.com
DSL2-17
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
DSL2-18

10. G.992.3 (ADSL2) – Rate & Reach
21.5 kft =
6.5 km
Diagram source:
www.aware.com
DSL2-19
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
DSL2-20

11. 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
DSL2-21
G.992.3 (ADSL2) Line Diagnostics
Changes:
• 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
DSL2-22

12. 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
DSL2-23
SELT/DELT Comparison
DSL2-24

13. 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
DSL2-25
SNR Margin
Capacity 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
DSL2-26

14. Power Cut Back
14
Power Cut Back 12
10
Power Cut Back [dB]
8
Measured Power Cut
Back
6 Predicted Cutback for
26 AWG cable
4
2
0
0
00
50
00
50
00
50
0
0
0
25
50
75
10
12
15
17
20
22
Distance 26 awg [feet]
• 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
DSL2-27
Fast Path versus Interleaved Path
• Dual paths exist within the ADSL standard
DSL2-28

15. 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
DSL2-29
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
DSL2-30

16. Superframe
DSL2-31
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
DSL2-32

17. 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
DSL2-33
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
DSL2-34

18. 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
DSL2-35
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)
DSL2-36

19. Annex Summary
#1 - 5 Bins #6 - 31 #32 - 64 #65 - 255 #256 - 512
ANNEX TYPE =0 =25.875 =138.0 =280.3 =1.104 to
Hz kHz kHz kHz 2.208 MHz
A (NA, EU, Asia) POTS POTS UP DOWN DOWN DOWN
B (Germany) ISDN ISDN ISDN UP DOWN DOWN
C (Japan) TCM- POTS UP DOWN DOWN N/A
ISDN
I (Japan ADSL) TCM- POTS UP DOWN DOWN DOWN
ISDN
I (Japan ADSL2) - UP UP DOWN DOWN N/A
I (Japan - UP UP DOWN DOWN DOWN
ADSL2+)
J (All Digital) - UP UP UP DOWN DOWN
L (RE-ADSL2) POTS POTS UP DOWN DOWN N/A
M (ADSL2+) POTS POTS UP UP DOWN DOWN
More Upstream
DSL2-37
Automode
Loop
CO DSLAM CPE
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 mode
5. CPE line at 1.1 Mbps (a 160% improvement over
ADSL1)
DSL2-38

20. Summary of Rate/Reach
VDSL2 100Mbps
2.4 km
8 kft
3.0 km
10 kft
4.3 km
14 kft
DSL2-39
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 DSL2-40

21. 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)
DSL2-41
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
DSL2-42

22. 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
DSL2-43
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)
DSL2-44

23. 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
DSL2-45
VTU-R Transmit (Upstream)
North America (NA)
25 kHz <PSD1> 138-276 kHz
DSL2-46

24. VTU-O Transmit PSD (Downstream) NA
30000
DSL2-47
VDSL2 Frequency Plan (Europe)
DSL2-48

25. VDSL Spectrum
• Frequency Plan 998
138kHz 3.75MHz 5.2MHz 8.5MHz 12MHz
DSL2-49
VDSL2 Proposed Rate/Reach
• rate
2200 ft
= 670m
DSL2-50

26. DSL Configuration
Design 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 increases
2) 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
DSL2-51
DSL Deployment Model
1. ILEC/CLEC sends CPE to customer for self install
2. ILEC/CLEC drives to customer site for the install
3. 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)
DSL2-52

27. 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?) DSL2-53
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
DSL2-54

28. 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
DSL2-55
• blank
DSL2-56

29. DSL2-57