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Stein Intro xDSL 3. 1 Introduction to x DSL Part III Yaakov J. Stein Chief Scientist RAD Data Communications.

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Presentation on theme: "Stein Intro xDSL 3. 1 Introduction to x DSL Part III Yaakov J. Stein Chief Scientist RAD Data Communications."— Presentation transcript:

1 Stein Intro xDSL 3. 1 Introduction to x DSL Part III Yaakov J. Stein Chief Scientist RAD Data Communications

2 Stein Intro xDSL 3. 2 Introduction to xDSL I Background history, theoretical limitations, applications II Modems line codes, duplexing, equalization, error correcting codes, trellis codes III xDSL - What is x? x=I,A,S,V - specific DSL technologies competitive technologies

3 Stein Intro xDSL 3. 3 Quick recap Lecture 1 How did we get to where we want to go? How far can we go? Lecture 2 How can we get there? Lecture 3 How can we get there? What do we do when we get there?

4 Stein Intro xDSL 3. 4 Quick Review DSL leaves concept of using 4KHz analog line Use UTP as general transmission line Rate limited by line loss thermal noise NEXT crosstalk FEXT crosstalk RF ingress (AM broadcast, ham, etc.) misc (splices, bridged taps, echo, filters, sync)

5 Stein Intro xDSL 3. 5 Introduction to xDSL III Applications Deployment topologies IDSL HDSL, HDSL2, SDSL ADSL, G.lite VDSL competitors (cable modems,wireless) HPNA

6 Stein Intro xDSL 3. 6 The Baby Bells had a problem : cable TV companies started offering 10 Mbps Internet access Internet seen as potential future market RBOC’s Plan: HFC to every home by 1996! This didn’t happen costs grew regulatory problems no standardization LEC’s had lower operating expenses What could be done?

7 Stein Intro xDSL 3. 7 Telco Alternatives Fiber, coax, HFC COST: $10K-$20K / mile TIME: months to install T1 COST: >$5K/mile for conditioning TIME: weeks to install DSL COST:  0 (just equipment price) TIME:  0 (just setup time)

8 Stein Intro xDSL 3. 8 Analog (or V.90) modems UTP subscriber line CO SWITCH network/ ISP router modem PSTN modem CO SWITCH

9 Stein Intro xDSL 3. 9 xDSL System Reference Model POTS SPLITTER UTP CO SWITCH DSLAM xTU-C network/ ISP router xTU-R POTS SPLITTER PSTN PDN POTS-RPOTS-C WAN x = H, A, V,... Analog modem


11 Stein Intro xDSL Network Reference Model PDN (Premises Distribution Network) is ethernet or USB WAN is typically ATM or FDDI (even though FDDI is LAN protocol) Internet is TCP/IP HDSL connects to DACS and to CSU Many interconnect possibilities (may impact modem design) full STM, full ATM, full packet network, packet-ATM-packet, etc. Example, FR WAN, ATM over UTP, Ethenet PDN Modems should be cell pumps, not bit pumps (also need CIF protocol to tunnel ATM through Ethernet)

12 Stein Intro xDSL Splitter Splitter separates POTS from DSL signals Must guarantee lifeline POTS services! Hence usually passive filter Must block impulse noise (e.g. ring) from phone into DSL ADSLforum/T1E1.4 specify that splitter be separate from modem No interface specification yet (can’t buy splitter and modem from different vendors) Splitter requires installation Costly technician visit is the major impediment to deployment G.lite is splitterless ADSL

13 Stein Intro xDSL xDSL - Maximum Reach

14 Stein Intro xDSL Examples of Realistic Reach More realistical design goals (splices, some xtalk) 1.5 Mbps 18 Kft 5.5 Km (80% US loops) 2 Mbps 16 Kft 5 Km 6 Mbps 12 Kft 3.5 Km (CSA 50% US loops) 10 Mbps 7 Kft 2Km 13 Mbps 4.5 Kft 1.4 Km 26 Mbps 3 Kft 900 m 52 Mbps 1 Kft 300 m ( SONET STS-1 = 1/3 STM-1)

15 Stein Intro xDSL xDSL flavors

16 Stein Intro xDSL xDSL flavors

17 Stein Intro xDSL ITU G.99x standards G.991 HDSL (G HDSL G SHDSL) G.992 ADSL (G full rate G G.lite G.992.3,4,5 new) G.993 VDSL G.994 HANDSHAKE G.995 GENERAL (INFO) G.996 TEST G.997 PLOAM G.998 PNT (HPNA)

18 Stein Intro xDSL Some xDSL PSDs F (MHz) PSD (dBm/Hz) IDSL T1 HDSLHDSL2 ADSL

19 Stein Intro xDSL Line Codes PAM IDSL, HDSL (2B1Q) HDSL2 (with TCM and optionally OPTIS) SDSL QAM/CAP proprietary HDSL/ADSL/VDSL DMT ADSL G.lite VDSL line code war is still raging (but QAM seems to be winning)

20 Stein Intro xDSL T1/E1 DS1 rate 1 bit per symbol AMI Half duplex on each UTP Full duplex requires 2 UTP (4W) Simple DSP Linear equalization Needs conditioning Repeaters (every km)

21 Stein Intro xDSL IDSL Original DSL (1980s) 160 Kbps in 80 KHz BW resistance design reach (18Kft) popular in Europe, but not US 2 bit PAM called 2B1Q (2 Bits in 1 Quat) (Gray code) alternative line code: 4B3T (4 Bits in 3 Ternary symbols)

22 Stein Intro xDSL HDSL Replace T1/E1 DS1 service Use 2B1Q line code, DFE Full duplex on each pair with echo cancellation Full CSA without conditioning/repeaters more complex DSP (250 MIPS) ANSI: 2 pairs for T1 (each 784 Kbps) ETSI: 1, 2, 3 or 4 pairs Most mature of DSL technologies

23 Stein Intro xDSL HDSL vs T1(AMI) T1 HDSL

24 Stein Intro xDSL HDSL - continued HDSL is repeaterless T1/E1 Major application - multiline POTS Reach is CSA (less than ADSL!) Can add doublers to extend range Other applications: PBX extension digital local loop campus networks Internet

25 Stein Intro xDSL HDSL2, SDSL, SHDSL, OPTIS Customers request HDSL service that is single UTP HDSL at least full CSA reach spectrally compatible w/ HDSL, T1, ADSL, etc. Variously called HDSL2 (ANSI) SDSL Symmetric DSL (ETSI) SHDSL Single pair HDSL (ITU) This is the DS1 service that will last!

26 Stein Intro xDSL OPTIS Overlapping PAM Transmission with Interlocking Spectra A solution that achieves these goals 16 level PAM with 517K baud rate very strong (512 state, >5 dB) TCM 1D for low (216  sec) latency (speech) strong DFE tailored spectra (fits between HDSL and T1) partially overlapped (interlocking) spectra folding (around f b /2) enhances SNR! upstream bump for spectral compatibility

27 Stein Intro xDSL OPTIS - continued

28 Stein Intro xDSL OPTIS - continued

29 Stein Intro xDSL ADSL Asymmetric - high rate DS lower rate US Originally designed for video on demand Almost retired due to lack of interest …but then came the Internet Studies show DS:US should be about 10:1 full rate ADSL kbps US, 6-8 Mbps DS G.lite 512 Kbps US, 1.5 Mbps DS ADSL could mean All Data Subscribers Living

30 Stein Intro xDSL Why asymmetry? NEXT is the worst interferer stops HDSL from achieving higher rates FEXT much less (attenuated by line) FDD eliminates NEXT All modems must transmit in the SAME direction A reversal would bring all ADSL modems down Upstream(US) at lower frequencies and power density Downstream (DS) at high frequencies and power

31 Stein Intro xDSL Why asymmetry? - continued US DS PSD (dBm/Hz) F(MHz)

32 Stein Intro xDSL Echo cancelled ADSL FDD gives sweet low frequencies to US only and the sharp filters enhance ISI By overlapping DS on US we can use low frequencies and so increase reach Power spectral density chart

33 Stein Intro xDSL ADSL - continued ADSL system design criterion BER (1 error every 2 days at 6 Mbps) Raw modem can not attain this low a BER! For video on demand: RS and interleaving can deliver (error bursts of 500  sec) but add 17 msec delay For Internet: TCP can deliver high raw delay problematic So standard defines TWO framers fast (noninterleaved ) and slow (interleaved) buffers

34 Stein Intro xDSL ADSL standard ITU (G.dmt) G.992.1, ANSI T1.413i2 standard First ADSL data implementations were CAP Standard is DMT DMT allows approaching water pouring capacity DMT is robust DMT requires more complex processing DMT may require more power

35 Stein Intro xDSL DMT Discrete Multitone is a form of FDM (Frequency Domain Multiplexing) Discrete Multitone is a form of MCM (MultiCarrier Modulation) It uses many different carriers, each modulated QAM Each tone is narrow low baud rate (long frame) channel characteristics are constant over tone Number of bits per tone chosen according to water pouring Put more bits where SNR is good

36 Stein Intro xDSL DMT - continued DMT is OFDM (Orthogonalized FDM) Carrier spacing is precisely baud rate Center of tone is precisely the zero of all other sincs ICI minimized ISI minimized by having a long interframe guard time DMT modem can be efficiently implemented using FFT DFT is mathematically equivalent to a bank of filters Filtering is equivalent to cyclic convolution So use cyclic prefix rather than guard time

37 Stein Intro xDSL DMT - continued time frequency

38 Stein Intro xDSL ADSL DMT Baud rate (and channel spacing) is KHz US uses tones (below 30 KHz reserved) DS uses 256 tones (FDM from tone 33, EC from tone 8) POTSPOTS USDS

39 Stein Intro xDSL DMT misc. bit handling ((de)framer, CRC, (de)scrambler, RS, (de)interleaver) tone handling (bit load, gain scaling, tone ordering, bit swapping) QAM modem (symbolizer, slicer) signal handling ( cyclic prefix insertion/deletion, (I)FFT, interpolation, PAR reduction) synchronization (clock recovery) channel handling (probing and training, echo cancelling, FEQ, TEQ)

40 Stein Intro xDSL RADSL Rate Adaptive ADSL Not variable rate (not small fast variations) Increases percentage of useable lines Fine for Internet access but not for video on demand Standard ADSL supports 32Kbps steps RADSL provides management protocols

41 Stein Intro xDSL G.lite ITU (G.lite) G.992.2, UAWG ADSL compatible DMT compatible using only 128 tones 512 Kbps US / 1.5 Mbps DS Still much faster than V.34 or V.90 modems No splitter required! Certain features removed for simplicity simpler implementation (only 500 MIPS < 2000 MIPS for full rate)

42 Stein Intro xDSL New ADSLs ITU has continued development of G.dmt.bis, G.lite.bis Should become G.992.3, G.992.4, G ADSL2 Longer reach with higher rate ( Mbps) 4D 16-TCM constellations, Stronger RS FEC Lower framing overhead (programmable 4-32Kbps overhead) Power cutback standby mode Algo improvements (e.g. real-time tone re-ordering, relocatable pilot tone) ADSL+ Uses more BW for higher bitrates for short reaches double BW (512 bins) - double speed (24 Mbps!) Annex J Symmetric 3 Mbps

43 Stein Intro xDSL VDSL Optical network expanding (getting closer to subscriber) Optical Network Unit ONU at curb or basement cabinet FTTC (curb), FTTB (building) These scenarios usually dictates low power Rates can be very high since required reach is minimal! Proposed standard has multiple rates and reaches

44 Stein Intro xDSL VDSL - rate goals Symmetric rates Kft (1.4 Km) 13 3 Kft (900 m) 26 1 Kft (300 m) Asymmetric rates (US/DS) 0.8/ Kft (1.8 Km) 1.6/ Kft (1.4Km) 3.2/26 3 Kft (900 m) 6.4/52 1 Kft (300 m)

45 Stein Intro xDSL VDSL - Power issues Basic template is -60 dBm/Hz from 1.1MHz to 20 MHz Notches reduce certain frequencies to -80 dBm/Hz Power boost on increase power to -50 dBm/Hz Power back-off reduces VTU-R power so that won’t block another user ADSL compatibility off use spectrum down to 300 KHz

46 Stein Intro xDSL VDSL - duplexing In Japan and campus applications can operate TDD (ping pong) SDMT Synchronous DMT (2 KHz frame can be heard in adjacent pairs or hearing aids) Rest of world PSTN only FDD is allowed Can divide US and DS into 2 areas (e.g. ADSL) or more Need guard frequencies because of clock master/slave problems Zipper - large number of interleaved frequency regions (even on a bin by bin basis)

47 Stein Intro xDSL VDSL line code wars VDSL AllianceVDSL Coalition DMTQAM MORELESS robust to noisepower capacitycomplex spectral compatibility expensive IPRA/D bits With no complexity constraints probably equivalent

48 Stein Intro xDSL T1E1.4 draft T1.424 T1E1.4 has released a 3-part “trial use” draft standard Part 1 Common Specifications Part 2 Single Carrier Modulation Part 3 Multicarrier Modulation Objective tests have been specified (VDSL Olympics) –Test definition may determine results SCM is NOT spectrally compatible with ADSL Present SCM implementations are more mature –the tests should be of technology, not products MCM may be more robust in certain noise settings The trials should be finished by July-August 2003 –ITU and IEEE are waiting for the results

49 Stein Intro xDSL G (G.hs) Handshaking Universal flexible method for initialization Includes tone negotiation for capability identification common mode identification exchange of nonstandard information line probing (line code dependent) Currently integral part of ADSL and G.lite Anticipated that future ITU DSL modems will support as well

50 Stein Intro xDSL G.997 (PLOAM) Physical Layer Operation Administration and Maintenance Includes physical layer management (SNMP based) configuration, fault and performance administration 4 management interfaces optional OAM channel far end management Currently integral part of G.992 (ADSL) family Anticipated that future ITU DSL modems will support as well

51 Stein Intro xDSL G (G.test) Universal testing procedure for xDSL modems Finds margins in presence of POTS signaling impulse noise cross-talk from other services geographical position dependent test loops and wiring models Currently integral part of G.992 (ADSL) family Anticipated that future ITU DSL modems will support as well

52 Stein Intro xDSL ISDN defined BONDING of 2B channels to one 128Kbps line G (SHDSL) Annex E has physical layer bonding ITU objectives: 1) be higher layer agnostic 2) be backward compatible with the present 2-wire G.shdsl Annex E solution 3) different rates on different pairs 4) be applicable to all DSL families, not just SHDSL 5) have low latency and overhead (to support TDM) 6) support dynamic addition and removal of pairs If succeeds no need for layer 2+ aggregation protocols (ATM-IMA, MLFR, MLPPP, 802.3ad etc) with high overhead, high latency, same rates for each pair, no dynamic addition/deletion support, etc.

53 Stein Intro xDSL cVoDSL Standard VoDSL sends TDM over ATM layer Channelized VoDSL reserves N 64Kbps channels (N=1..4) PRO Implemented on-chip (no GW), higher voice quality, lower delay CON Consumes BW even if not used baseband physical layer POTS cVoDSL DSL physical layer ATM layer AAL1AAL2AAL5 IP layer VoATM VoIP

54 Stein Intro xDSL Competitors and non-DSL technologies

55 Stein Intro xDSL G.998 (G.pnt,HPNA) Studies show that about 50% of US homes have a PC 30% have Internet access, 20% have more than one PC! Average consumer has trouble with cabling HomePNA de facto industry standard for home networking Computers, peripherals interconnect (and connect to Internet?) using internal phone wiring (user side of splitter) Does not interrupt lifeline POTS services Does not require costly or messy LAN wiring of the home Presently 1 Mbps, soon 10 Mbps, eventually 100 Mbps!

56 Stein Intro xDSL HPNA HPNA 1.0 (98Q3) has average data rate Mbps Line code is PPM (pulse position modulation) Each pulse is 4 cycles at 7.5 MHz (shaped) time between pulses 3.27  sec <  < 6.07  sec Can co-exist with full-rate ADSL and G.lite HPNA 2.0 (ITU G.pnt) Mbps QAM line code HPNA 3.0 up to 100 Mbps Specification not yet finalized


58 Stein Intro xDSL Cable modems - continued Line Code (nonstandard, IEEE ) QPSK/16 QAM US 1.5 Mbps (raw) 64/256 QAM DS 30 Mbps (raw) QPSK control channel FDD (US low frequencies, DS high frequencies) BW to CM is shared Performance degrades when too many users

59 Stein Intro xDSL Cable modems - continued DOCSIS - Data Over Cable System Interface Specification Evolving specification for high-speed data-over-cable systems DOCSIS 1.0 designed for transparent bi-directional IP traffic –3.2 MHz channel, 5.12 Mbps (QPSK) DOCSIS 1.1 enhancement: –3.2 MHz channel, Mbps (16-QAM) –BW management features for QoS multimedia applications DOCSIS 2.0 improved modem –6.4 MHz channel, Mbps (64-QAM / 128-QAM+TCM / S-CDMA) –symmetric upstream and downstream, –increased noise immunity Cable modems are not allowed to monitor each other so Ethernet (CSMA/CD) is not possible

60 Stein Intro xDSL MMDS Wireless cable services are only minor competition Services originated when telcos wanted to get into CATV Multichannel Multipoint Distribution System (Wireless CATV) 2.6 GHz (SHF) frequencies 54 Mbps DS (33 uncompressed video/data channels) Upstream traffic requires expensive subscriber transmitters Line of site range Technical problems: weather, trees

61 Stein Intro xDSL LMDS Local Multipoint Distribution System (Cellular TV) 28 GHz frequency short-distance version of MMDS uses small cells small cell size requires many transmission antennas most suitable for business LAN extension

62 Stein Intro xDSL DBS Direct Broadcast Satellite Geosynchronous satellites already used for digital TV POTS return connection High powered transmitter return connection Significant propagation delay Low earth orbit (LEO) satellites Minimal delays Lower power uplink transmitters Too expensive for residential use

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