xDSL Technical Overview Oct 08 1 DSL Market Drivers & Enablers B-Box / SAI VDSL over OSP Twisted Pair SAI CO NID/Splitter POTS Res. Gateway OR IP DSLAM NID/Splitter ADSL over OSP Twisted Pair STB Consumer drivers IPTV More upstream data High-speed internet data Consolidated billing Service Provider Drivers Telco's desire to compete with Cable companies Additional service(s) = revenue STB STB Enablers IC Technology advancements Leverage ADSL and extend frequency range/bitrate ITU standards finalized 2 DMT Discrete Multi-Tone Each one is controlled by the DSL protocol based on actual line conditions. BITS/TONE 15 Max Vf Upstream Downstream MHz 4.3125 Khz One sub-carrier, “tone” = 4.3125 Khz passband DMT uses 256 “tones” to carry bits/data for ADSL, 4096 for VDSL2 Each “tone” can carry up to 15 bits (QAM) 3 Signal Attenuation SNR is responsible for the performance Transmitted Signal Power Received Signal Power Signal to Noise Ratio (SNR) Received Noise Power 64 kHz MHz Frequency 4 Bits per Tone With good SNR we got more Bits Bits per tone Transmitted Signal Power 15 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 Received Signal Power can support. Received Noise Power . . . 0 64 kHz MHz Frequency 5 Standards Family ITU Name Ratified Maximum Speed capabilities ADSL G.992.1 G.dmt 1999 8 Mbps down 800 kbps up ADSL2 G.992.3 G.dmt.bis 2002 8 Mb/s down 1 Mbps up ADSL2plus G.992.5 ADSL2plus 2003 24 Mbps down (Amend 1, 29Mbps) 1 Mbps up ADSL2-RE G.992.3 Reach Extended 2003 8 Mbps down 1 Mbps up VDSL G.993.1 Very-high-data-rate DSL 2004 55 Mbps down 15 Mbps up VDSL1 -12 MHz long reach G.993.2 Very-high-data-rate DSL 2 2005 55 Mbps down 30 Mbps up VDSL2 - 30 MHz Short reach G.993.2 Very-high-data-rate DSL 2 2005 100 Mbps up/down 6 Technology ADSL - VDSL Frequency Ranges & Rates VDSL2 VDSL ADSL2+ ADSL 17.66MHz 25kHz 1.1MHz 2.2MHz 12MHz Frequency 30MHz Technology Freq range Max Rates Max # of carriers and Bin spacing ADSL 25kHz – 1.1MHz 800kbps up 8Mbps down 256 with 4.3125kHz bins ADSL2+ 25kHz – 2.2MHz 1Mbps up 24Mbps down 512 with 4.3125kHz bins Amend. 1 = 29 Mbps down VDSL(1) 25kHz – 12MHz 15Mbps up 55Mbps down 2782 with 4.3125kHz bins VDSL2 25khz – 30MHz 100Mbps up 100Mbps down 4096 with 4.3125kHz bins 3478 with 8.625kHz bins 7 What are VDSL2 – Key Features – Improvements to initialization, including a Channel Discovery phase and a Loop Diagnostics mode – Improved framing based G.992.3 (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 8 ADSL2+/VDSL/VDSL2 - Rate versus Reach 250 DS ADSL2+ (2.2 MHz) Symmetrical 100Mbit/s due to 30MHz spectrum 200 DS VDSL1 (12 MHz) DS VDSL2 (30MHz) Rate / MBit/s AWGN/-140dBm/Hz/ANSI-TP1 150 Improved mid range performance through Trellis coding and Generic Convolutional Interleaver 100 ADSL-like long reach performance due to Trellis coding and Echo Cancellation 50 0 Reach / m Reach / ft* 0 500 1000 1500 2000 2500 3000 3500 1600 3300 4900 6600 8200 9900 11,500 9 VDSL Rate and Reach AWG26, Gap = 12dB, 20-self, Tx PSD = -53 dBm/Hz 140 30 MHz 25 MHz 20 MHz 17.6 MHz 12 MHz 8.5 MHz 4.4 MHz 2.2 MHz 1.1 MHz 120 Rate (Mbits/s) 100 80 60 40 20 0 0 1 2 3 Loop Length (kft) 4 5 6 10 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.998.3 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 11 Ham Radio Notches Table 6-2/G.993.1 – Transmit notch bands Band start (kHz) Band stop (kHz) 1 800 2 000 3 500 4 000 7 000 7 300 10 100 10 150 14 000 14 350 18 068 18 168 21 000 21 450 24 890 24 990 28 000 29 700 12 Band Plans – VDSL 4-Band 3-Band 2-Band Band Plan (G.993.2, Annex A) 1-Band D1 U0 4-25 kHz U1 138-276 kHz 3.75 MHz D2 U2 5.2 MHz 12 MHz 8.5 MHz 6-Band 5-Band 4-Band 3-Band 2-Band Band Plan (G.993.2, Annex C) 1-Band D1 = Radio Notches U1 640 kHz 3.75 MHz D2 5.2 MHz U2 8.5 MHz D3 12 MHz U3 17.7-18.1 MHz 30 MHz U0 is used for VDSL Long Range Products (VLR) 13 Band Plans – VDSL 4-Band 3-Band 2-Band Band Plan 998 1-Band (G.993.2, Annex B) U0 25 kHz D1 U1 138-276 kHz 3.75 MHz D2 5.2 MHz U2 12 MHz 8.5 MHz 4-Band 3-Band 2-Band Band Plan 997 1-Band (G.993.2, Annex B) U0 = Radio Notches 25 kHz D1 U1 138-276 kHz 3.0 MHz U2 D2 5.1 MHz 7.05 MHz 12 MHz U0 is used for VDSL Long Range Products (VLR) 14 Band Plans for VDSL Frequencyplans Band-edge frequencies (As defined in the generic band plan) 997 998 f0 f1 f2 f3 f4 f5 kHz kHz kHz kHz kHz kHz 25 138 25 276 3000 5100 7050 12000 138 276 25 138 25 276 138 276 3750 5200 8500 12000 N/A 276 DS1 Opt US1 DS2 US2 f(MHz) f0 f1 f2 f3 f4 f5 T1544750-02 15 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 16 VDSL2 Some Favored Profiles Maximum aggregate downstream transmit power (dBm) Maximum aggregate upstream transmit power (dBm) Subcarrier spacing (kHz) Minimum net aggregate data rate (Mbit/s) Typical use case 8b +20.5 +14.5 4.3125 50 CO 17a +14.5 +14.5 4.3125 100 FTTN Annex A, Annex B (998): 1971 (8.5) N/A 30a +14.5 +14.5 8.625 200 FTTB Japan N/A 1205 (5.2) N/A N/A 1971 (8.5) 4095 (17.664) 2098 (18.1) 1205 (5.2) 2782 (12) 3478 (30) Annex C Index of highest supported downstream data-bearing subcarrier (upper band edge frequency in MHz (Informative)) Index of highest supported upsteam data-bearing subcarrier (upper band edge frequency in MHz (informative)) Index of highest supported downstream subcarrier (upper band edge frequency in MHz (informative)) Index of highest supported upstream subcarrier (upper band edge frequency in MHz (informative)) Note: While Annex C is specified as for Japan, other regions are using those profiles 17 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 18 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: Crosstalk from VDSL effecting ADSL: PSD management approach Exchange: OLT Optical Node DSLAM 20 to 25 M bps for VDSL VDSL Profile 17a VDSL Profile 8b ADSL2+ 19 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 20 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. 21 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 22 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. 23 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) 24 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) 25 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. 26 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. 27 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. 28 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-tomultipoint 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. 29 OLR – Dynamic Spectrum Management (DSM) 30 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 t0 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. Line 1 Frame #1 Error correction for Frame #1 Error correction for Frame #2 Frame #2 Line 2 Frame #1 Frame #3 Error correction for Frame #1 Frame #2 Frame #3 Error correction for Frame #3 X Frame #4 Error correction for Frame #2 X Frame #4 Error correction for Frame #4 X X Frame #5 Error correction for Frame #3 X X Frame #5 Error correction for Frame #5 Error correction for Frame #6 Frame #6 Error correction for Frame #4 Error correction for Frame #5 Frame #6 Time 31 INP – ADSL2+ Down-stream Significant Throughput Impact 32 INP – ADSL2+ Amendment 1 Down-stream Significant Throughput Impact 33 INP – ADSL2+ Up-stream Significant Throughput Impact 34 Impulse Noise Impairments 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 35 Transient – Long Term Interference Noise Transient or longer term noise sources make critical impacts on DSL service performance: •AM Radio SW Station at 13.615 MHz •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 36 A tap acts like a filter 0 -10 Clean pair -20 Insertion Loss (dB) -30 -40 -50 44ft tap -60 -70 -80 -90 0 1 2 3 4 5 6 7 8 9 10 Freq (MHz) 37 Longer taps = less impact 0 -10 Clean pair -20 Insertion Loss (dB) -30 -40 -50 -60 100ft tap 75ft tap -70 50ft tap -80 44ft tap Short taps (under 200 ft) have more impact on VDSL -90 0 1 2 3 4 5 6 7 8 9 10 Freq (MHz) 38