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1 xDSL Technical Overview Oct 08. 2 DSL Market Drivers & Enablers Service Provider Drivers  Telco's desire to compete with Cable companies  Additional.

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Presentation on theme: "1 xDSL Technical Overview Oct 08. 2 DSL Market Drivers & Enablers Service Provider Drivers  Telco's desire to compete with Cable companies  Additional."— Presentation transcript:

1 1 xDSL Technical Overview Oct 08

2 2 DSL Market Drivers & Enablers Service Provider Drivers  Telco's desire to compete with Cable companies  Additional service(s) = revenue SAI IP DSLAM B-Box / SAI VDSL over OSP Twisted Pair NID/Splitter POTS Res. Gateway STB Consumer drivers  IPTV  More upstream data  High-speed internet data  Consolidated billing Enablers  IC Technology advancements  Leverage ADSL and extend frequency range/bitrate  ITU standards finalized NID/Splitter OR ADSL over OSP Twisted Pair CO

3 3 DMT Khz Discrete Multi-Tone Each one is controlled by the DSL protocol based on actual line conditions. Vf Upstream Downstream MHz Khz passband One sub-carrier, “tone” = DMT uses 256 “tones” to carry bits/data for ADSL, 4096 for VDSL2 Each “tone” can carry up to 15 bits (QAM) 15 Max BITS/TONE

4 4 Signal Attenuation Received Noise Power Received Signal Power Transmitted Signal Power Frequency MHz64 kHz Signal to Noise Ratio (SNR) SNR is responsible for the performance

5 5 Bits per Tone Received Noise Power Received Signal Power Transmitted Signal Power Frequency MHz64 kHz With good SNR we got more Bits Bits per tone 15 0 As distance increases from the DSLAM, signals attenuate on the copper loop reducing difference between noise and the signal restricting the number of bits each DMT carrier can support....

6 6 Standards FamilyITUNameRatifiedMaximum Speed capabilities ADSLG.992.1G.dmt19998 Mbps down 800 kbps up ADSL2G.992.3G.dmt.bis20028 Mb/s down 1 Mbps up ADSL2plusG.992.5ADSL2plus Mbps down (Amend 1, 29Mbps) 1 Mbps up ADSL2-REG.992.3Reach Extended20038 Mbps down 1 Mbps up VDSLG.993.1Very-high-data-rate DSL Mbps down 15 Mbps up VDSL1 -12 MHz long reach G.993.2Very-high-data-rate DSL Mbps down 30 Mbps up VDSL MHz Short reach G.993.2Very-high-data-rate DSL Mbps up/down

7 7 ADSL - VDSL Frequency Ranges & Rates 25kHz 1.1MHz 2.2MHz 12MHz Frequency 30MHz ADSL2+ ADSL VDSL VDSL2 TechnologyFreq rangeMax RatesMax # of carriers and Bin spacing ADSL25kHz – 1.1MHz800kbps up 8Mbps down 256 with kHz bins ADSL2+25kHz – 2.2MHz1Mbps up 24Mbps down 512 with kHz bins Amend. 1 = 29 Mbps down VDSL(1)25kHz – 12MHz15Mbps up 55Mbps down 2782 with kHz bins VDSL225khz – 30MHz100Mbps up 100Mbps down 4096 with kHz bins 3478 with 8.625kHz bins Technology 17.66MHz

8 8 What are VDSL2 – Key Features –Improvements to initialization, including a Channel Discovery phase and a Loop Diagnostics mode –Improved framing based G (ADSL2) with improved overhead channel –Support of Impulse Noise Protection (INP) up to 16 symbols –Support for a MIB-Controlled PSD mask mechanism for in-band spectral shaping –Support for an optional extension of the USO band to 276 kHz –Improved FEC capabilities, including a wider range of settings for the Reed-Solomon encoder and the inter-leaver

9 9 ADSL2+/VDSL/VDSL2 - Rate versus Reach Reach / m Rate / MBit/s DS ADSL2+ (2.2 MHz) DS VDSL1 (12 MHz) DS VDSL2 (30MHz) AWGN/-140dBm/Hz/ANSI-TP1 Symmetrical 100Mbit/s due to 30MHz spectrum ADSL-like long reach performance due to Trellis coding and Echo Cancellation Improved mid range performance through Trellis coding and Generic Convolutional Interleaver ,500 Reach / ft*

10 10 VDSL Rate and Reach

11 11 Bonded Service  A way to increase rate and reach over single pair limitations  Multiple physical pairs carrying a portion of the total bit stream.  Three approaches: –G.998.1, ATM based –G.998.2, Ethernet based –G Time –division Inverse Mux  VDSL will use an Ethernet approach with “muxing” at the TC layer with a new aggregation and rate matching function.  May not achieve double the rates due to VDSL cross talk in the same binder group

12 12 Ham Radio Notches

13 13 Band Plan (G.993.2, Annex A) Band Plan (G.993.2, Annex C) U0 is used for VDSL Long Range Products (VLR) Band Plans – VDSL D1U1D kHz3.75 MHz5.2 MHz8.5 MHz U kHz 12 MHz 2-Band 3-Band 4-Band U2 1-Band D1U1D2 640 kHz3.75 MHz5.2 MHz8.5 MHz 12 MHz 2-Band 3-Band 4-Band U2 1-Band U3 D MHz 30 MHz 5-Band 6-Band = Radio Notches

14 14 Band Plan 998 (G.993.2, Annex B) Band Plan 997 (G.993.2, Annex B) U0 is used for VDSL Long Range Products (VLR) Band Plans – VDSL D1U1D kHz3.75 MHz5.2 MHz8.5 MHz U0 25 kHz 12 MHz 1-Band 2-Band 3-Band 4-Band U2 D1U1D kHz3.0 MHz5.1 MHz7.05 MHz U0 25 kHz 12 MHz 2-Band 3-Band 4-Band U2 1-Band = Radio Notches

15 15 Frequency- plans Band-edge frequencies (As defined in the generic band plan) f0f0 f1f1 f2f2 f3f3 f4f4 f5f5 kHz N/A276 Band Plans for VDSL

16 16 VDSL2 Profiles Profiles are specified to allow transceivers to support a subset of the allowed settings and still be compliant with the recommendation. The specification of multiple profiles allows vendors to limit implementation complexity and develop implementations that target specific service requirements. The eight VDSL2 profiles (G.993.2) : 8a, 8b, 8c, 8d, 12a, 12b, 71a, 30a, define a set of configurations for transmit power and band plan. Service Providers are now using these terms

17 17 VDSL2 Some Favored Profiles Note: While Annex C is specified as for Japan, other regions are using those profiles

18 18 VDSL2 Spectrum Capability For exchange deployment –VDSL2 spectrally compatible with ADSL/ADSL2 (138kHz to 1.104MHz) and with ADSL2+ (138kHz to 2.208MHz) For cabinet deployment –VDSL2 spectrally compatible with cabinet-based ADSL2+ –Power control needed to ensure spectrum compatibility with exchange based services (138kHz to 2.208MHz) –Achieved by shaping the cabinet signals by a factor based on the electrical distance between the exchange and cabinet –Degree of shaping defined via MIB control (G.997.1) –Enables VDSL2 to comply with regulatory requirements –VDSL2 PSD shaping currently being investigated by various European and Asian operators

19 19 VDSL2 PSD Shaping  PSD shaping in VDSL2 facilitates coexistence between ADSL/2/2+ from the CO with ADSL2 from the cabinet.  PSD shaping functionality exists already in ADSL2+ –Compared to ADSL2+ VDSL2 has extended the parameter range –Likely to be amended to ADSL2+ as well  Different level of transmit power makes disturbance in the same binder – need adjustment.  One configuration example: Exchange: OLT DSLAM Node VDSL Profile 8b VDSL Profile 17a Optical ADSL2+ 20 to 25 M bps for VDSL Crosstalk from VDSL effecting ADSL: PSD management approach

20 20 OLR - Dual Latency (Fast and Interleaved Paths) Dual Latency refers to bearer channels that can have different latency treatments as defined by such things as interleave depth, INP settings and FEC configurations.  Fast path has low latency (<1ms). –Good for voice traffic. –People perceive delay negatively during a conversation. –Losing (small amounts of) data is not critical. Most CODECs will disguise lost data by replaying the previous audio.  Interleaved path has more latency (up to 10ms) but has better immunity to disturbers such as impulses. –Guaranteed to correct errors due to impulses <250μs. –Good for data and video. –Data and video are tolerant of delay (not "delay variation" that's jitter) but are not tolerant of lost data

21 21 On-Line Reconfiguration (OLR)  Reconfiguration takes four forms: Bit Swapping (BS), Seamless Rate Adaptation (SRA). Dynamic Rate Repartitioning (DRR) and Dynamic Spectrum management (DSM)  BS reallocates data and power (i.e. margin) among the allowed sub ‑ carriers without modification of the higher layer features of the physical layer. Bit Swapping reconfigures the bits and fine gain parameters without changing any other PMD or PMS ‑ TC control parameters.  SRA is the ability to change data rates in real-time based on monitoring changing line conditions and adjusting such things as bit swapping, DMT symbol bit assignments and DMT bins in use without losing frame sync.  DRR is used to reconfigure the data rate allocation between multiple latency paths by modifying the frame multiplexer control parameters. DRR can also include modifications to the bits and fine gain parameters, reallocating bits among the sub-carriers. DRR does not modify the total data rate, but does modify the individual latency path data rates.  DSM enables transceivers to autonomously and dynamically optimize their settings for both channel and neighboring systems, reducing crosstalk significantly.

22 22 OLR - Seamless Rate Adaptation (SRA)  SRA dynamically monitors line conditions and adjusts bit rates to take advantage of improved conditions and reduces bit rates if necessary without loss of sync.  Parameters and their typical values used for SRA –Downshift margin up = 3 dB –Downshift interval up = 60 seconds –Downshift margin down = 3 dB –Downshift interval down = 60 seconds –Upshift margin up = 3 dB –Upshift interval up = 60 seconds –Upshift margin down = 3 dB –Upshift interval down = 6 seconds  The effect is to increase bit rate performance

23 23 OLR - Dynamic Rate Repartitioning (DRR)  DRR monitors the bandwidth on a connection and reallocates the bandwidth per path allowing the available bandwidth to be used more efficiently. –It achieves this by modifying the framing parameters and by using bit swapping. –The reallocation of the bandwidth is done seamlessly without disturbing the user’s applications (video stream, VoIP call, surfing the net). –The total delivered bandwidth is not changed. It will reallocate the bandwidth assuring each application gets the highest possible QOS.

24 24 Dynamic Spectrum Management (DSM)  Static Spectrum Management (SSM) setup as part of network engineering guarantees that all of the DSL lines in binder are spectrally compatible. Since services running on the DSL lines are dynamic, static management typically wastes bandwidth.  DSM takes advantage of dynamically changing conditions and improves the wasted channel capacity left by SSM.  The ultimate DSM solution requires monitoring of the line conditions by a central processing unit as well as the individual modems monitoring line conditions as well.  The central DSM unit monitors: –Line margin –Tx Power Levels –Bits/tone tables –Insertion loss/tone –Noise/tone –Actual PSD levels/tone –Errored seconds –Known service items such as bridge taps, loop lengths, and binder service area (so they know what other services are in the same binder)

25 25 Dynamic Spectrum Management (DSM)  There are 4 levels of DSM coordination between multiple DSL lines –Level 0 Static Spectrum Management (SSM) –Level 1 Autonomous power allocation (Single –user) –Level 2 Coordinated power allocation (Multi – user) –Level 3 Multi-pair, multiple-input, multiple-output (MIMO)

26 26 DSM (The Four Levels) Level 0  Level 0: The performance of one individual pair is optimized without considering the other pairs in the binder –Rate Adaptive (RA) and Margin Adaptive (MA) modes of operation. RA mode – All available power is used to maximize rate at the required margin MA mode – All available power is used to maximize margin at a fixed rate.

27 27 OLR – DSM (The Four Levels) Level 1  Level 1: Each pair in a binder manages power so as to avoid crosstalk with the other pairs in the binder. This will lead to an increased total capacity in the binder. –Power Adaptive (PA) or Fixed Margin (FM) and Iterative Water Filling (IWF) are modes of operation. PA – Power is minimized while maintaining a fixed rate and noise margins that are specified in a given range. IWF – Very similar to PA except IMF does not adhere to a fixed PSD, therefore ‘boosting’ is allowed. IWF can increase the power in used tones by reallocating power from unused tones.

28 28 OLR – DSM (The Four Levels) Level 2  Level 2: Similar to level 1; Here however, the central DSM center considers the other pairs line conditions as well. –Optimal Spectrum Management (OSM) aka Optimal Spectrum Balancing (OSB) The central DSM knows the cross-talk paths, the loop lengths, and the service requirements of each pair in the binder. All the used spectra is optimized by the central DSM by setting the PSDMASK parameters for each pair based on the DSM prediction of the complete binder performance. So for example, a short line may be told to use the higher frequencies even though the lower frequencies would have been used if only IWF was applied.

29 29 OLR – DSM (The Four Levels) Level 3  Level 3: The central DSM processes all of the signals from all the pairs in a binder at once. All transmitters and/or receivers must be co-located. –The central DSM will jointly process all of the signals in the binder rather than processing each line individually. –The binder is considered a whole entity aka (MIMO or vectoring). All the signals are combined into a vectored signal and processed together. With the joint processing, it is now possible to predict the induced crosstalk on the other lines. That predicted crosstalk signal can be subtracted from the actual received signal to reduce the crosstalk. –This can be implemented in a point-to-point configuration or a point-to- multipoint configuration. Point-to-point – All processing is done at the receiver. Point-to-multipoint – One CO multiple CPE all processing is done at the CO.

30 30 OLR – Dynamic Spectrum Management (DSM)

31 31 Impulse Noise Protection  The basic idea with INP is to separate (in time) the data and the corresponding error correction bytes for that data. This helps ensure that if an impulse occurs at time t 0 only the data will be corrupted; the RS correction bytes allow the data to be fixed. –More memory is needed to store the data while waiting for the error correction data. –INP causes the data to be delayed. Frame #1 Time Frame #2Frame #3Frame #4Frame #5Frame #6 Error corr- ection for Frame #1 Error corr- ection for Frame #2 Error corr- ection for Frame #3 Error corr- ection for Frame #4 Error corr- ection for Frame #5 Error corr- ection for Frame #6 Frame #1Frame #2Frame #3Frame #4Frame #5Frame #6 Error corr- ection for Frame #1 Error corr- ection for Frame #2 Error corr- ection for Frame #3 Error corr- ection for Frame #4 Error corr- ection for Frame #5 Line 1 Line 2 X X X X X X

32 32 INP – ADSL2+ Down-stream Significant Throughput Impact

33 33 INP – ADSL2+ Amendment 1 Down-stream Significant Throughput Impact

34 34 INP – ADSL2+ Up-stream Significant Throughput Impact

35 35 Impulse Noise I mpairments  VDSL is more susceptible to impulse noise events due to it’s use of a wider frequency spectrum than ADSL. Noise sources are being analyzed in several forms: –REIN (Repetitive Electrical Impulse Noise) Less than 1 ms in duration No bit errors desired INP mitigation –PEIN (Prolonged Electrical Impulse Noise) 1 to 10 ms in duration No bit errors desired INP mitigation –SHINE (Single Isolated Impulse Noise Event) Duration greater than 10 ms Due to duration of events, bit errors will typically occur No loss of sync is desired

36 36 Transient – Long Term Interference Noise Transient or longer term noise sources make critical impacts on DSL service performance: AM Radio Many operate, both base band frequency of station and difference signal between two strong stations, in the ADSL band, stronger at night Short Wave Radio Many short wave radio stations operate in VDSL bands from 3.2 MHz to 21.5 MHz SW Station at MHz

37 37 Clean pair 44ft tap A tap acts like a filter

38 38 Clean pair 100ft tap 75ft tap 50ft tap 44ft tap Longer taps = less impact Short taps (under 200 ft) have more impact on VDSL


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