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  • 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 / toneDMT - Discrete Multi-Tone ModulationOrthogonal Sub-channels Spaced@ 4.3125 kHz frequencySNR (Signal to Noise Ratio) Marginsignal above the backgroundnoise floor (i.e. +8dB)QAM Modulated With 2 - 14 BitsNote: 64-QAM 4-QAM 22 = 4 Constellation Points 214 = 16,384 Constellation Points DSL2-4
  • 3. Three Down Stream (DS) Speeds1. Theory – Possible 256 bins, 12 Mbps max2. 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” loading3. 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 DSL2-5Quad 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 15Bit 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 DSL2-11G.992.5 Upstream PSD (ADSL2+) Power Spectral Density (PSD) PSDindBm/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 Frequency0 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 DSL2-15G.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 DSL2-17G.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 DSL2-19G.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 DSL2-21G.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 operatorBenefit:• 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 DSL2-23SELT/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 DSL2-25SNR 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-channelTotal Rate = Sum of Bits-per-Bins x 4,000 DSL2-26
  • 14. Power Cut Back 14Power 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 DSL2-29Interleave• 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 DSL2-31G.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 MHzA (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 ISDNI (Japan ADSL) TCM- POTS UP DOWN DOWN DOWN ISDNI (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 DOWNMore 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 DSL2-39DSM (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) DSL2-41SHDSL• 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 DSL2-47VDSL2 Frequency Plan (Europe) DSL2-48
  • 25. VDSL Spectrum• Frequency Plan 998 138kHz 3.75MHz 5.2MHz 8.5MHz 12MHz DSL2-49VDSL2 Proposed Rate/Reach• rate 2200 ft = 670m DSL2-50
  • 26. 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 DSL2-51DSL Deployment Model1. 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) DSL2-52
  • 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?) DSL2-53EFM• 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