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Broadband Access Networks and Services
EE Spring 2004 Broadband Access Networks and Services Chapter 2 Twisted-Pair based Access Networks Byeong Gi Lee Seoul National University
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2. TP-based Access Network
Limitation of POTS and ISDN Digital Loop Carrier DSL Technologies – IDSL, HDSL, SDSL, ADSL, G.Lite, VDSL, and Comparisons ADSL Access Network, Architecture, Components, and Protocol Model Spectrum Allocations Modulation Techniques Applications, Challenges, and Penetration BGL
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Structure of Access Network
ADSL : Asymmetric Digital Subscriber Line DBS : Direct Broadcast Satellite FTTC : Fiber To The Curb HFC : Hybrid Fiber Coaxial LMDS : Local Multipoint Distribution System MMDS : Multi-channel Multipoint Distribution System MSO : Multiple Service Operator TP-based AN Digital DBS Fiber or Wireless MMDS/LMDS LMDS only Hub Station DBS STB/ MMDS/LMDS STB 64Kbps ISDN Adaptor ISDN Line MSO /CO Analog Modem 56Kbps 앞 절에서 소개한 기술을 개략적으로 도시한 그림입니다. 6Mbps ADSL Modem Home Terminal Coax 30Mbps 640Kbps Cable Modem Fiber HFC 3Mbps ONU Coax or Copper Fiber VDSL Modem 52Mbps FTTC/FTTO 3Mbps BGL
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Access and Backbone Infrastructure
BGL
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Limitation of POTS and ISDN
Limitation in existing subscriber lines Restrictive for high-speed service Limited data-carrying capacity of 56kbps using V.90 Analog mode and suppressing filters above 3,400Hz Limitation of POTS Customer connected over thin-wire pairs (26guage, 0.5mm) Local loops are bundled in binder groups (feeder part) Limitation of ISDN services Not possible to provision ISDN and POTS in same local loop Internet Problems for POTS and ISDN Both carries data in circuit mode (voice switch) BGL
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Digital Loop Carrier T1 or HDSL base feeder (connecting CO and RT) BGL
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xDSL Advanced modulation technology based bandwidth expansion (128kbps to 52Mbps) xDSL easier to install than ISDN needs inside wiring work and copper line cleaning Variations depending on symmetry of upward/downward data rates (ADSL vs SDSL) and the location of equipment (ADSL vs VDSL) Supports POTS using splitter (split flter). But G.Lite can eliminate splitter. HDSL can replace T1/E1 without repeaters. BGL
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Configuration of xDSL T1/E1 HDSL ADSL VDSL Central Office (PSTN) BGL
End User (POTS) Central Office (PSTN) TP (2 pairs) CO Repeater Line Repeater Line Repeater T1/E1 0.3~1km 1~1.8 km 0.3~1km End User (POTS) Central Office (PSTN) TP (2 pairs) HDSL HDSL CO Unit HDSL RT Unit End User (Video) Headend (Video) ADSL CO Unit ADSL TP (1 pair) ADSL RT Unit xDSL(Digital Subscriber Line, x=family member; A, H, S, U, V)는 기존의 트위스트 페어 전화선을 사용하는 디지털 가입자 선로(Digital Subscriber Line) 기술 집합을 의미한다. xDSL 기술은 비대칭형 전송방식인 asymmetric DSL(ADSL), 대칭형 전송 방식인 high-data-rate DSL(HDSL) 및 single-line DSL(SDSL), 단거리에서 초고속 데이터 전송방식인 very-high-rate DSL(VDSL), 및 전송선로 특성에 따라 전송속도가 가변이 되는 rate-adaptive DSL(RADSL) 등으로 구별된다. PSTN POTS End User (Video) Headend (Video) Optical Network Unit VDSL VDSL CO Unit TP (1 pair) VDSL RT Unit PSTN SPF POTS BGL
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IDSL ISDN Digital Subscriber Line is a cross point between ISDN and xDSL Made available with the introduction of ISDN 2B + D basic rate access (BRA), 144kbps+16kbps B: 64kbps for voice or data D: 16kbps for call control or packet data Transmission rate of 80 ksps 2B1Q modulated Travels over 5.4 km over 24 gauge (.5mm) BGL
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HDSL Comparable with T1/E1 lines
Mbps rate transmission with 2 pairs Can replace T1/E1 lines without repeaters For T1 rate (1.5Mbps), two TP wires are necessary For E1 rate (2Mbps), three TP wires are necessary 2B1Q Modulated, CAP, DMT 2B1Q: 3.6km, CAP:5.5km over 24 gauge Interference problem when bundled in large size BGL
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SDSL Symmetric (or Single-line) HDSL (SHDSL, SDSL)
Two-wire (single pair) implementation of 2B1Q or CAP Data rate of 384kbps~2Mbps (Sub-T1/E1 rates obtainable) HDSL2 (G.SHDSL) stadard Symmetric 2.3 Mbps over a single loop pair Symmetric 4.6 Mbps over two loop pair Echo cancellation and adaptive equalization BGL
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ADSL Up/down asymmetric bandwidth
For use in Internet, VOD like applications One pair - good for residential use 1.5/2 ~6/8 Mbps down, 16~820 kbps up Up to 5.4km without repeaters (0.5mm) DMT (standardized), CAP (market) modulation POTS split through split filter (SF) Rate-Adaptive DSL (RADSL) - line condition Universal ADSL (UADSL) - without split filter BGL
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ADSL G.Lite ITU G.992.2 Easy and consumer-installable due to no need of POTS splitters like in full-rate ADSL (UADSL) Offers the services of ADSL at a lower speed POTS service possible by reducing the transmission power when off-hook Fast retrain procedure: 1~2 s cessation of service Longer reach and much less power than full-rate ADSL BGL
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VDSL Very high data rate, (a)symmetric DSL
Drop line for FTTC application 13~52 (~155) Mbps down depending on distance 300 m to 1.5 km distance (from curb to home) CAP, DMT,QAM (DAVIC) modulation POTS split through split filter (SF) Standardization (DAVIC, ANSI T1E1.4, ETSI TM6, FSAN) BGL
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ADSL vs. G.Lite Full-Rate ADSL G.Lite ITU Specification ITU G.992.1
ANSI T1.413 ITU G.992.2 No ANSI specification Also known as G.dmt Splitterless ADSL POTS Yes, using a single splitter in home Yes, using microfilters at each analog handset Modulation scheme DMT Phones only after splitter freely connected anywhere Subbands 256 128 Downstream speed 6 Mbps, maybe more for shorter distances Up to T1 Upstream speed Up to 512 Kbps Professional installation Hopefully no Yes, for splitter and inside wiring BGL
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ADSL vs. VDSL POTS/ISDN, therefore requiring splitters Full-Rate ADSL
Modulation techniques Yes DMT, using 256 bands with 4 kHz spacing VDSL DMT, CAP, or QAM DMT modulation would use 256 band with 40 kHz spacing, or 2048 bands with 4 kHz spacing Dual latency Spectrum Allocation Up to 1 MHz Up to 30 MHz Downstream bit rate 2 to 3 Mbps Various up to Mbps Upstream bit rate Various up to T1 Various up to 6 Mbps Standardization ASNI T1.E1 ADSL Forum ITU G.992.1 ITU SG 15, G.vdsl, G.993 Distance to ONU Up to 5000 meters 300 to 1000 meters BGL
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Comparison of xDSL (1) Modulation Scheme ISDN 2B1Q 64 Kbps, 128 Kbps
ANSI T1.601 Uses 4B3Q coding in some European countries IDSL HDSL HDSL-2 SDSL(ETSI) Up to 2 Mbps 2 Mbps Downstream Bit Rate Upstream POTS Support Comments Uses ISDN TA Uses four wires; current T1 service PAM-16 Uses two wires; not rate- adaptable Yes Uses two wires; rate BGL
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Comparison of xDSL (2) G.Lite ADSL Mutiple Virual Line (MVL)
One Megabit Modem VDSL 2 Mbps 1.5 Mbps to 6Mbps DMT 512 Kbps Yes ITU G.992.2 CAP 64 Kbps to 800 Kbps Mostly Paradyne ANSI T1.413 768 Kbps Paradyne QAM 1 Mbps 320 Kbps Proprietary to Northern Telecom; residers in Nortel loop carrier system QAM/CAP 12.96 Mbps to 51.84 Mbps 3 Mbps Range of 300 meters for top speeds; ANSI T1.E1.4, ETSI and ITU Study Group 15 BGL
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Comparison of xDSL (3) * Distance for 0.5 mm (24 gauge) TP wires BGL
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ADSL-based Access Network
Switch 0~4 kHz Splitter Splitter PSTN Subscriber line DSLAM Data Comm. Network ATU-C ATU-R T1.413 Issue 2 : Down 25 ~ 1104 kHz, Up ~ 138 kHz UADSL : Down 138 ~ 552 kHz, Up ~ 138 kHz Subscriber line UADSL-R * DSLAM : Digital Subscriber Lines Access Multiplexer * ATU-C : ADSL Transceiver Unit, Central * ATU-R : ADSL Transceiver Unit, Remote * Splitter-less in UADSL BGL
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Generic ADSL Access Network Architecture
BGL
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ADSL Components ADSL Transceiver Units POTS splitter
Physical layer device for frequency allocation, echo cancellation, FDM, rate adaptation, etc. POTS splitter Lowpass/highpass filter that separates analog voice from ADSL frequencies DSL Access Multiplexer Houses a set of ATU-C interfaces, mux/demuxes traffic from multiple ATU-Cs onto a single high-speed trunk BGL
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Protocol Model for Data Services over ADSL
BGL
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Typical Protocol Stack for Access Network
BGL
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Bandwidth Requirement
Application File Type File Size Modem 28.8 kb/s ISDN 128 kb/s xDSL 384 kb/s 1.5 Mb/s 6.1 Mb/s All User 30 kB 8.3 sec 1.9 sec 0.63 sec 0.16 sec 0.04 sec Consumer Digitized Photo 125 34.7 sec 7.8 sec 2.6 sec 0.6 sec 0.2 sec Business User Word Files 250 kB 69.4 sec 15.6 sec 5.2 sec 1.3 sec 0.3 sec Telecommuter Videoconferencing 384kb/s No YES Telemedicine X-ray 5 MB 23.1 min 5.2 min 1.7 min 25.9 sec 6.5 sec Remote LAN Ac c ess Bulk File 20 MB 1.5 hr 20.0 min 6.9 min 26.0 sec * Acceptable response time < 3.0 sec BGL
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Concept of Spectrum Allocation
(Numbers for example) ISDN ADSL (Down) Power Spectra POTS ADSL (Up) ADSL(Asymmetric Digital Subscriber Line)은 “비대칭형디지틀가입자회선”으로 해석되는데 엄밀한 의미에서 회선자체를 말하는 것이 아니라 정확히 말하면 전화회선의 미사용 대역폭을 이용하여 데이터속도를 혁신적으로 증가 시키는 전화선 양단의 모뎀을 지칭한다. ADSL은 1989년 Bellcore에서 전화선으로 동영상 즉 VOD서비스를 제공하겠다는 그 당시는 가히 혁명적인 개념에서 태동된 기술이다. 그러나 Contents의 빈약, 수요기반의 미성숙, VOD기술의 불완전으로 인하여 세인의 관심사에서 멀어져 사장된 기술로 인식되어 오다가 지난 95년부터 인터넷 붐이 일어나면서 다시 빛을 발하기 시작했다. ADSL의 가장 큰 특징은 전화국과 가입자간의 데이터 전달속도가 비대칭이며, 상향측 속도는 640kbps속도를 가지나, 하향 전달속도는 최고 9Mbps속도까지 제공 가능하다는 것이다. 하향전달속도는 전화국에서 가입자까지의 전화선의 거리, 직경, 브리지 탭의 유무, Interference의 세기 등 다양한 요소에 의하여 영향을 받으며, 특히 신호감쇄는 라인의 길이가 증가하고 주파수가 높을수록 급격히 증가한다. ADSL모뎀은 전화선의 직경이 0.5mm(24AWG)인 경우 각 1.5Mbps하향신호는 5.5km까지 전달할 수 있다. 한국통신의 가입자 평균거리가 2.5km이고 95%가 5.5km이내임을 감안한다면 ADSL 도입을 위한 선로상태는 유리한 편이며, 특히 브리지 탭이 없는 것은 ADSL기술을 채용하는 데 있어 큰 장점으로 작용할 것이다. 4 10 80 100 200 1000 kHs BGL
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Spectrum Allocations for xDSL
FTT Exchange, FTT Cabinet BGL
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ADSL Operation (1) Two services of ADSL: Voice Service (1)
transparent access to legacy voice service high-speed digital service Voice Service (1) Provision of voice service relatively simple In-home configuration Frequencies below 3400Hz shunt by POTS splitters to POTS wiring at home and to voice switch at CO NID (or NT) by telco powering, ATU-R by local powering Voice service not to be subject to home wiring impairments Protection of NID from lightening required not to damage home electronics. So professional assistance needed for splitter installation BGL
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ADSL Operation (2) Voice Service (2)
Three possible locations of POTS splitter: LPF at NID and HPF at ATU-R; both filters in ATU-R; both filters in NID Three constraints: local powering ATU-R; voice not to be subject to impairments of home wiring LPF relatively large, so does not fit into NID These three constraints suggest POTS splitter and ATU-R should be separated BGL
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ADSL Operation (3) One proposal from British Telecom BGL
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ADSL Operation (4) Digital Service (1) 1. Determine latency:
Video traffic subject to burst error, so interleaving and FEC used. ANSI provided 500microsecond burst protection against impulse noise, creating 20ms latency. But data service has no such requirement as higher-layer protocols can perform error correction, - delay of only 4ms. So ADSL provides two logical data channels – fast (4ms) and slow (20ms) Video on slow channel due to FEC and interleaving Data on fast channel only with (de)modulation delay ATU-R determines which latency type to take at start-up BGL
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ADSL Operation (5) Digital Service (2) 2. Determine bit rate:
RADSL adapts to the line condition via a negotiation process When powered on, ATU-R probes the line to determine signal carrying capacity. Signal-carrying capacity is a function of distance, noise, and allowable margins Negotiation goes between ATU-C and ATU-R for maximum sustainable bit rate (out of four start-up rates, ANSI) Entire negotiation within 20s. BGL
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ADSL Operation (6) Digital Service (3) 3. Perform auto-configuration:
Configuring IP addresses and software filters for ATU-R Relatively straightforward since each user has a dedicated ATU-C Manually configured by DSLAM or some form of software tunnel between ATU-R and a device Method differs depending whether ATU-R or the end system is IP-aware If ATU-R and PC is IP-aware DHCP client is one autoconfiguration technique BGL
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ADSL Operation (7) Digital Service (4) 4. Digital Data Transfer
After startup complete, data transferring ATU-R accepts data from home networking over an Ethernet, ATM25, or other digital protocols, encapsulates, and then sends out. MAC protocol is not required unlike HFC Dynamic rate adaptation: ATU-R and ATU-C renegotiation during data transmission by periodic testing of line conditioning -- retraining time will be required in support of this. BGL
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Modulation Techniques
2B1Q (2 binary, 1 quaternary) DMT (discrete multi-tone modulation) CAP (carrier-less amplitude and phase modulation) QAM (quadrature amplitude modulation) QPSK BGL
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2B1Q -3 -1 +1 +3 Bits Quads BGL
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DMT (1) DMT: Sub-channel based data rate allocation BGL TWISTED-PAIR
Bits/chan Bits/chan Atten Frequency Frequency Frequency TWISTED-PAIR with TAP, AM/RF, and XTALK Bits/chan Atten AM Bits/chan TAP xtalk Frequency Frequency Frequency BGL
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DMT (2) DMT Transceiver Block Diagram S BGL T’=TDMT/2N Transmitted
signal Encoder and buffer b=RT 2N Point IDFT Parallel to serial converter DAC LPF R b/s N QAM Symbols 2N Times Domain Samples T’=TDMT/2N Decoder DFT Serial to Parallel T’ Channel S Noise Received N개의 부채널을 가진 기본적인 DMT송,수신 system은 위 그림과 같다. 입력 bit stream(R bps)은 b bits(b=RT)의 블럭 단위로 쪼개어져 저장된다. T(secs)는 symbol period를 1/T(frequency)는 symbol rate를 나타낸다. 한 블럭에 할당된 b bits는 N~개의 부채널에 각각 bi(i=1,2....N) bits씩 각부채널의 SNR 특성에 따라 분배된다. 그 다음 각각의 부채널의 bi bits는 QAM constellation상의 한 점인complex subsym -bol X(=│Xi│?Xi)로 encode 된다. 예를 들어 i번째 부채널에 bi = 4bits씩이 할당되게 되면, 현재의 b bits 블럭의 입력 비트열중 i 번째 부채널에 할당된 4bits에 해당하는 데이터(e.g: 1011)를 16-QAM의 1011에 해당 하는 subsymbol로 encode 하게 된다. 일단 N개의 부채널에 b bits가 bi bits씩 할당되고 QAM symbol Xi로 encoding되고 N개의 symbol을 IFFT를 사용하여 변조하게 된다.전송채널을 통해 실제로 전송되는 신호는 time domain에서 real 신호여야 하기때문에 , 할당된 N~개의 complex subsymbol Xi의 conjugate symmetric 신호를 N + 1부터 2N까지 배열하여 N-point IFFT를 함으로써 N개의 real-valued time domain samples, n(n=0,1, N-1)을 얻는다. DMT modulator의 sampling rate 1/T'는 NT'=T로부터 1/T'=N/T, 즉symbol rate의 N배가 됨을 알 수 있다. BGL
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DMT (3) Features Issues frequency efficiency
symbol length per sub-channel longer frequency selective noise avoided Issues complexity, power consumption timing and synchronization critical ANSI standard BGL
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CAP (1) CAP Transceiver Block Diagram + Encoder Inphase filter
Quadrature + DAC LPF Input signal Decoder Output ADC Decision device CAP방식은 single carrier 방식으로서 송신부에서 2개의 baseband 신호를 in-phase와 quadrature filter를 이용하여 passband spectral shaping하여 전송하는 방식이다. QAM과 CAP의 신호는 같은 구조 이나 단지 차이점은 QAM의 경우에는 쉐이핑 필터의 입력에 ejwcnT가 곱해진 신호를 사용하는 반면CAP에는 ejwcnT가 곱해지지 않은 raw심볼을 사용한다. BGL
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CAP (2) 16CAP BGL ... b2 b3 b0 b1 b2 b3 b0 b1 b2 b3 b0 b1... t
quadrant point within quadrant symbol Qn 11 01 +3 10 11 b2 b3 01 00 current state 10 00 +1 00 01 -3 -1 +1 +3 In 01 00 00 10 11 -1 10 11 10 -3 01 11 BGL
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QAM 16QAM : Downstream in DAVIC VDSL In-Phase I n Filter + Data Band
Symbol Pass Signal Input Encoder _ Filter Output Q n Quadrature Filter Q n 11 01 +3 10 11 b2 b3 increasing time 01 00 current lsb msb TC layer state byte alignment 10 00 +1 00 01 b2 b3 b0 b1 b2 b3 b0 b1 b2 b3 b0 b1 b2 -3 -1 +1 +3 I n quadrant 01 00 -1 00 10 point within quadrant 11 10 symbol n (0..3) symbol n+1 (0..3) 11 10 -3 01 11 BGL
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QPSK QPSK: Upstream DAVIC VDSL Transmit I n Filter + cos Data Band
Symbol Pass Signal Oscillator Input Encoder _ Filter Output sin Q n Transmit Filter +1 -1 00 01 11 10 b0 b1 I n Q b1 b0 increasing time lsb msb byte alignment TC layer symbol n n+1 n+2 n+3 BGL
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CAP vs. DMT CAP DMT Power consumption Lower, fewer gates
Higher peak/average, but will likely narrow gap Forward carriers 1 256 Return carriers 32 Increment 320 Kb 32 Kb Adaptive equalizers Needed None Licensing Globespan Many sources Standardization In process ITU and ANSI BGL
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xDSL Applications (1) High-speed Internet Access Telecommuting
residential and business area Intranet access to link Remote Office and Branch Office (ROBO) low cost, high throughput LAN-to-LAN connectivity Telecommuting Small Office / Home Office (SOHO) BGL
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xDSL Applications (2) On-demand type applications
VOD, home shopping, tele-education, Interactive TV Frame relay / ATM network access Leased line provisioning (HDSL/SDSL) replacing conventional T1/E1 leased line FTTC using VDSL BGL
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Technical Challenges of xDSL (1)
End-to-end loop qualification impacted by Loop length, loading coils, quality of E2E splicing of wiring segments, multiple changes of wire gauge, home wiring, age, corrosion, hostile binder groups, crosstalk, and bridged taps… Crosstalk Near-end crosstalk (NEXT) Far-end crosstalk (FEXT) Bridged Taps Y form branch => source of echo BGL
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Technical Challenges of xDSL (2)
Powering remote terminals Local power used to power DSL equipment; battery backup Spectral masking Long-term narrowband interference such as, AM radio and amateur radio ingress Notching out specific frequencies Impulse noise Short-term interference with duration of 100ms with peak power of 10mv ART-R maintenance Software upgrading such as, algorithms BGL
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xDSL Penetration Worldwide (1)
Sources from Point-Topic 77 million broadband lines worldwide at June 2003 60% of all broadband lines are xDSL (46.7 million) DSL lines grew by 30% in the first half of 2003, cable modems by 16.4% Fast increase in Japan and China Growth appears to be slowing in Korea and USA Expected 60 million xDSL subscribers by end of 2003 BGL
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xDSL Penetration Worldwide (2)
BGL
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xDSL Penetration Worldwide (3)
BGL
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xDSL Penetration Worldwide (4)
BGL
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xDSL Penetration Worldwide (5)
USA BGL
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xDSL Penetration Worldwide (6)
China (1) BGL
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xDSL Penetration Worldwide (7)
China (2) BGL
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xDSL Penetration Worldwide (8)
Japan (1) BGL
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xDSL Penetration in Korea (1)
11 million broadband access subscribers (Jun. 2003) 6.2 million xDSL (56.5%), 3.8 million Cable (34.5%) Source: 정보통신부 *아파트LAN: LAN based Broadband Internet Service BGL
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xDSL Penetration in Korea (2)
Subscribers for Service Providers BGL Source: 정보통신부
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xDSL Penetration in Korea (3)
Service Providers and Base Technologies BGL Source: 정보통신부
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Access Network Architecture (2)
Typical technology-independent protocol stack A typical protocol stack for an access network. ATM applications Application/services SNMP, TFTP, DHCP, security management, etc TCP/UDP IP, ICMP PPP ARP LLC Link security AAL5 and ATM MAC TC Transmission convergence (TC) Physical BGL
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Service Architecture over ADSL (1)
Basically a p2p switched transmission technology IP over PPP over HDLC over ADSL or IP over ATM over ADSL ADSL intended to be used as access technology for Internet or LAN access in conjunction with analog telephony service Various architectural models possible to meet the specific service offerings, interconnection to the backbone networks, and strategic direction of a network provider BGL
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Service Architecture over ADSL (2)
A plausible communications model for data over ADSL An example communications protocol model for data services over ADSL. Note that this model is fairly generic to work on any physical medium IP Any data link layer or ATM with TC * PPP HDLC AAL5 MAC PMD TC 802.2 LLC 803.3 MAC 802.3 10BaseX Switch # and/or router Internet/ WAN ADSL-C modem ADSL-R modem Home terminal Copper wire Optionally, a standards-based ATM UNI interface can be provided to connect directly to an ATM backbone Switch can be a LAN, a frame relay switch, or an ATM switch BGL
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Service Architecture over ADSL (3)
ATU-C: encoding and modulating the DS data and combining the analog POTS signal; in US, demodulating the signal received from the customer and outputting a data stream and POTS signal Three main architecture options Bit-synchronous mode ATM cell mode Packet mode Type of mode is independent of underlying line encoding method used BGL
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Service Architecture over ADSL (4)
Generic reference architecture at logical model A generic ADSL access network architecture. Access node * Service-specific interfaces Access node can be co-located with the CO switch, or be remoted in the distribution plant. Internet backbone ATM network Private leased-line Other networks (e.g., FR) ATU-C ATU-R Premises LAN cable wiring PC Set-top PSTN Passive split To phones Network interface Copper loop BGL
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Service Architecture over ADSL (5)
Bit-Synchronous Mode Traditional circuit-switched network digital hierarchy Interface with either a backbone voice or data network via existing CBR circuit-switched services Plesiochronous digital hierarchy supported in ADSL DS1 (1.544 Mbps); E1 (2.048 Mbps); DS2 (6.312 Mbps); E2 (8.448 Mbps) An application will typically use the appropriate bandwidth from the digital hierarchy meeting the bandwidth demand Data applications such as Internet and LAN interconnect supported in this mode BGL
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Service Architecture over ADSL (6)
Packet-based Transport over ADSL MUX in the access node adapts the protocol carried over ADSL to one of the commonly used packet transport services Switching and/or routing of variable-length layer 2 frames and/or layer 3 packets over an ADSL link PPP and FR are the most popular L2 protocols (HDLC-like) supporting any of L3 protocols (IP, IPS,..) PPP encapsulation: allows many different protocols to be transported over p2p links FUNI encapsulation: variable-size frame to be transmitted is encapsulated in FUNI frame BGL
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Service Architecture over ADSL (7)
ATM-based Transport over ADSL ATU-R provides a native ATM interface to the user device or a legacy LAN interface with segmentation and reassembly (SAR) functionality Edge switch ATM multiplexer in access node Concentration and ATM layer routing function Alternatively, SAR and network layer routing can be provided in CO such as DSLAM On access side: multiplicity of service protocols (TCP/IP, PPP, FR, ATM cell relay, ATM circuit emulation) over a variety of physical layer protocols (HDSL, ADSL, DS1) On backbone side: standard ATM user-network interface for transport to ATM switch, which can connect to ATM backbone BGL
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