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xDSL

xDSL. Network reference model. Access provider. Core network. Access network. Service provider. Customer Premises Network. TP cable fiber WLL. Transport exchange. Network provider. Evolution of Access Network. Evolution based on Twisted Pairs(TP)

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xDSL

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  1. xDSL

  2. Network reference model Access provider Core network Access network Service provider Customer Premises Network TP cable fiber WLL Transport exchange Network provider

  3. Evolution of Access Network • Evolution based on Twisted Pairs(TP) • Evolution based on optical fiber • Evolution based on wireless network

  4. 국내 초고속 가입자 현황 xDSL HFC APT LAN 위성 합계 KT 4,625,841 498,306 5,632 5,129,782 하나로 통신 1,184,629 1,359,675 386,951 2,931,255 두루넷 1,284,963 8,543 1,293,506 온세통신 482,172 6,967 489,139 드림라인 73,075 87,554 3,663 164,192 데이콤 69,630 74,653 144,283 부가통신사업자 4,836 363,632 4,388 372,856 별정통신사업자 49,205 124,854 174,059 합계 5,937,586 3,647,626 1,108,328 5,632 10,699,172 점유율(%) 55.50 34.09 10.36 0.05 100 2003년 2월말 자료: 한국전산원

  5. DSL 기술의 배경 • One way to avoid enormous investment for installing optical fiber local loop is to use the traditional copper local loop. • The twisted local loop is actually capable of handling bandwidths up to 1.1 MHz, but the filter installed at the end of the line by the telephone company limits the bandwidth to 4KHz. If the filter is removed, however, the entire 1.1 MHz is available for data and voice communications. • Thus, DSL technology provides higher data rate in addition to support POTS at the same time.

  6. Various xDSL(1) • ISDN • 2B+D • 23B+D • HDSL(High data rate Digital Subscriber Line) • ADSL(Asymmetric Digital Subscriber Line) • SDSL(Symmetric Digital Subscriber Line) • VDSL(Very high data rate Digital Subscriber Line) • RADSL, MDSL, IDSL, UADSL

  7. Various xDSL(2) • ADSL2 • ADSL2+ • VDSL2

  8. Characteristics of major xDSL TP(2 pairs) Central Office (PSTN) End User (POTS) T1/E1 CO Repeater Line Repeater Line Repeater 0.3~1km 1~1.8km 0.3~1km Central Office (PSTN) TP(2 pairs) End User (POTS) HDSL HDSL CO Unit HDSL RT Unit Headend (Video) End User (Video) ADSL/ SDSL TP(1 pair) ADSL CO Unit ADSL RT Unit PSTN POTS Headend (Video) Optical Network Unit End User (Video) VDSL TP(1 pair) VDSL CO Unit VDSL RT Unit PSTN POTS

  9. HDSL • T1/E1 rate with 2 TP pairs • Internet access, LAN service • Mainly used for leased line service for business customers • Covers 3.5km(12kf) using 196KHz bandwidth without any repeater • Less expensive than the standard T1/E1 leased line service • dual duplex: two transceiver • 2B1Q Modulation

  10. SDSL • T1/E1 rate with single pair • Data rate; 160kbps-2.048Mbps(symmetrical) • Distance: less than 3km • 2B1Q

  11. ADSL • Asymmetric bi-directional digital subscriber line • Data rate:1.5- 8 Mbps (downstream), 16-640 kbps (upstream) depending on distance and line quality • Distance is up to 5.5km(18kft) • DMT(G.992.1, G.992.2) Headend ADSL CO Unit End User TP 1pair ADSL RT Unit 1.5 ~ 8 Mbps 16 ~ 640kbps POTS PSTN

  12. Frequency Bandwidth • Since data transmission is done on the frequency between 30KHz and 1MHz, ADSL provides data services as well as POTS at the same time. POTS downstream upstream 138 30 1104 3.3 0.3 frequency (KHz)

  13. ADSL Modem and DSLAM

  14. Line coding • Discrete Multitone(DMT) • ITU standard(G.992.1, G.992.2) • Combines QAM and FDM. • The whole bandwidth is divided into 256 channels. • For upstream data and control the channel 6 to 30 are used, each using 4KHz. • With QAM modulation, available bandwidth is 24x4000x15 = 1.44Mbps. • For down stream, channels 31 to 255 are used, and we can achieve up to 224x4000x15=13.4Mbps

  15. DMT

  16. Bandwidth Division

  17. ADSL2 • Data rate: 8Mbps(down), 800kb/s(up) • Improve ADSL for stability rather than speed. • Improved initialization • On-line reconfiguration • Framing • DMT(G.992.3, G.992.4)

  18. ADSL2+ • Improve the downstream data rate of ADSL. • Bandwidth for downstream data transmission: 2MHz • downstream data rate • 16Mb/s, 1.2km • 10Mb/s, 1.8km • 7Mb/s, 2.5km • Upstream, 1.5Mb/s • DMT(G.992.5) • However, there is little or no improvement of speed for loops beyond 2.5km.

  19. VDSL • Very high data rate digital subscriber line • Because of distance limitation, fiber cable should be installed up to the curb, and from there twisted pair lines are used up to subscribers. • Depending on distances, up to 13-52Mbps(down), 1.5-2.3Mbps(up) • Bandwidth: 10MHz • VDSL line coding standards • ANSI: DMT • IEEE: DMT (EFM-Cu for short-reach) • ETSI: DMT/QAM • ITU-T G.993.1 • Because VDSL is used for short distance, there are many technical issued such as crosstalk to be solved.

  20. 1 X MDSL 64~2,048kbps ~6km 1 X 1.544Mbps(T1) HDSL ~3.5km 2 X 2.048Mbps(E1) RADSL 128k~1Mbps 128k~8Mbps ~5.5km 1 O UADSL 128~512kbps 128k~1.5Mbps ~6km 1 O VDSL 640~2.3Mbps 13~52Mbps ~1.4km 1 O xDSL Comparison Data rate distance types TP POTS down up IDSL 128kbps ~5.5km 1 X SDSL 768kbps ~3.5km

  21. New ADSL VDSL 50Mb/s VDSL2 10Mb/s ADSL2+ ADSL 6Mb/s 1Mb/s ADSL2+ 1 km 0.5 6 4 7 2 5 3 거리

  22. VDSL2 • Adopts ADSL ‘s new features • Backward compatibility to ADSL family • Possible new features • Frequency beyond 12MHz • 100Mb/s at 1km • Etc.

  23. Migration Strategy Premises Curb Wire Plant Neighborhood up to 8Mbps Copper Loop DLC up to 8Mbps DLC DSLAM ONU up to 52Mbps FTTC 155Mbps and beyond FTTH

  24. DSL Terminology xDSL = x Digital Subscriber Line ADSL = Asymmetric Digital Subscriber Line RADSL = Rate-Adaptive Digital Subscriber Line UAWG = Universal ADSL Working Group (universal ADSL, ADSL Lite, G.Lite, splitterless ADSL) SDSL = Symmetric Digital Subscriber Line HDSL = High Bit-Rate Digital Subscriber Line HDSL2 = High Bit-Rate Digital Subscriber Line, 2nd generation SHDSL = Single-pair High Bit-Rate Digital Subscriber Line IDSL = ISDN Digital Subscriber Line VDSL = Very High-Speed Digital Subscriber Line DSLAM = Digital Subscriber Line Access Multiplexer xDSL =Physical layer technologies allowing transport of digital information over the copper loop.

  25. HFC(Hybrid fiber-coaxial)

  26. HFC Overview • HFC networks use a hybrid of fiber optic and coaxial cable to make the cable network bidirectional (two-way). The use of fiber-optic cable reduces the need for amplifiers down to 8 or less. • Coaxial network has a tree & branch structure. • An area served by a SO is divided into several cells. • The size of a cell is decided by the number of subscribers. Set top box TV splitter ONU Head end Cable modem PC

  27. HFC 망 splitter TBA Outdoor optical RTX (ONU) Distribution center (SO) Tap-off PP Coaxial cable Optical RTX broadcast H/E Power supply CMTS CM ISP Cell 1 PP: program provider SO: system operator Cell N CM: cable modem CMTS: cable model termination system TBA: trunk bridge amplifier

  28. Components • ONU(Optical Network Unit) • Transforms between optical signals and RF signals in a cell. • TBA • Guarantee the loss of line signal of coaxial cables. • Splitter • Split one RF signal into more than two RF signals. • Tap-off • It distributes equally RF signal into subscriber terminals.

  29. Frequency bandwidth Analog broadcast Digital broadcast Value added services Internet upstream 750 MHz 5 450 552 42 54 • The downstream data occupies 450-552MHz band. This band is divided into 6MHz. • The upstream data occupies 5-42MHz band, which is also divided into 6MHz channels. • The 5-42MHz frequency band for upstream is very susceptible to noises by consumer electronics devices and signals caused by HAM, CB radios. • For this reason, The low bit rate modulation technique such as QPSK is used for stability.

  30. Data rates Data rates depending on modulation techniques of DOCSIS modems Downstream upstream 1.5MHz 6MHz bandwidth QPSK 64QAM 256QAM 16QAM modulation 27Mbps Data rate 5Mbps 40Mbps 2.5Mbps

  31. Characteristics • One cell serves up to 500-2500 subscribers. • Bidirectional transmission • Limitation of data rate • When 100 subscribers use at the same time, data rate is reduced to less than 300kbps(downstream). • Because of tree & branch structure, the transmission quality is deteriorated by signal interruption.

  32. 국내 HFC 망 연혁 • 1995년 종합유선방송(케이블TV) 사업 개시 • PP(Program provider): 프로그램 공급자 • SO(System operator): 지역 방송국 • 광역시, 대도시 1차 53개 지역 • 지역 중소 도시 2차 24개 지역 • 중계유선 3차 • NO(Network operator): • 케이블 TV 분배망(PP-SO): 파워콤, KT(위성) • 케이블 TV 전송망(SO-가입자): 파워콤, SO의 HFC 망 • 케이블 모뎀을 통한 인터넷 사업 시작 • 1997년 KEPCO 양방향 시버 서비스 성공 • 1998년말 두루넷(KEPCO의 HFC망 사용) 사업 시작 • 1999년 하나로, 2000년 온세 통신 등 다수 사업자 참여 • HFC망: KEPCO 1차 지역, 데이터 HFC망 구축 • 2000-2002년 초고속 가입자 사업 활성화 • KT 시설분 SO 매각, 중계유선의 SO 전환 • 파워콤 분리 • 인터넷 가입자 증가로 데이터 HFC망 시설 폭증(하나로, 두루넷, SO 등 HFC 자가망 구축) • 2003년 디지털 케이블 TV 도입 개시 자료: 파워콤㈜ KRNET2004발표자료

  33. 국내 인터넷 가입자 현황 • 전체 가입자 증가와 마찬가지로 현재 완만한 증가 추세로 인터넷 가입자의 포화 상태에 이르렀음을 알 수 있다. 2001.2 2003.12 2004.4 2000.12 2002.12 1,143만 398만 1,040만 1,118만 780만 전체가입자 139만 262만 383만 402만 355만 HFC망가입자 자료: 파워콤㈜ KRNET2004발표자료

  34. Standards • CableLabs, DAVIC, IEEE 802.14, ATM Forum, IETF의 IP over Cable Data Network • CableLabs(Cable Television Laboratories Inc.) • Non profit organization composed of cable modem manufacturers. • CableLabs standards are adapted by ANSI, ITU-T • Also performs certificates. • DOCSIS(Data Over Cable Service Interface Spec.) • DOCSIS 1.0(1999): • DOCSIS 1.1: • DOCSIS 2.0(2001): • Digital settop box standards: Opencable • Cable Network Interface Standard(SCTE40/DVS313)

  35. DOCSIS cable modem • DOCSIS 1.0(1999년) • First commercialized standards • Bidirectional data transmission • DOCSIS 1.1(2001년) • Improve OoS functions • DOCSIS 1.0 can be upgraded to DOCSIS by software. • DOCSIS 2.0(2002년) • Improve upstream data rate: 30Mbps • Symmetrical bidirectional service • H/W upgrade

  36. HFC MAC • Credit-based MAC • For upstream transmission, the headend grants the right to send data to cable modems. • CRA(Collision Resolution Algorithm) • When cable modems send credit requests collision may happen, When it happens, the headend detects the collision, and notifies cable modems of it. Then the cable modems backoff and retry after random intervals.

  37. Future • Speed improvement • Frequency bandwidth can be expanded upto 1.5Gbps, the speed can be increased upto 100Mb/s. • Downsizing of cells • The current distance from ONU to subscribers which is about 1km will be decreased to less than 500m. • Improve network monitoring system.

  38. SDH (SONET)

  39. Multiplexing of Telephone Lines

  40. Multiplexing of Digital Signals

  41. Digital Hierarchy Table 6.1 DS and T lines rates

  42. Digital Hierarchy (Europe) Table 6.2 E line rates

  43. Synchronous Digital Hierarchy(SDH) PDH SDH DS-0 0.064 1 DS-1 T-1 1.544 24 DS-2 T-2 6.312 96 DS-3 T-3 44.736 672 DS-4 T-4 274.176 4032 STM-1 OC-3 155.52 STM-4 OC-12 622.08 STM-16 OC-48 2488.32 STM-48 OC-192 9953.28

  44. Synchronous Digital Hierarchy(SONET)

  45. SONET transport network

  46. TDM-based transport network Home POP(주노드국) CO(수용국) ADSL (1.5M~8Mbps) DSLAM 2.5Gbps (POS) GES GSR B-RAS Internet 수용국 Edge Router (7500) LAN A DS3/ OC3 MTU DS3/ OC3 T1 ADM OC3/ OC12 LAN B T1 (1.544Mbps) FLC ADM FLC STM-4 (2.5G) STU T1 T1 1.544 Mbps SONET/SDH OC3 LAN C DSC (D/MUX) ADM 동선 DSC (D/MUX) T1 1.544 Mbps ADM CSU 수용국 LAN D CSU TDM multiplexing/Circuit switching No Statistical multiplexing 64Kbps 64Kbps 1.544Mbps 1.544Mbps 1 1 1 1 … … STS-1 (45M) STS-1 24 24 … … STS-N STS-N OC-N … … 28 28 T1 1.544 Mbps T1 1.544 Mbps STS-1 STS-1

  47. SONET frame

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