ADSL Introduction

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Information about ADSL Introduction

Published on November 30, 2007

Author: luie


固定網路與行動網路趨勢 :  固定網路與行動網路趨勢 Zsehong Tsai(蔡志宏教授) National Taiwan University Department of Electrical Engineering Introduction of Broadband Access:  Introduction of Broadband Access Broadband Access (寬頻接取網路) designed to provide Internet Users to access ISP backbone nodes may be used to carries TCP/IP, or other pure data services, such as Media on Demand(MOD) Non-switched (always-on) or timely charge The provider of Broadband Access services is a combination of : Telecomm. Operator + ISP + CPE provider (optional) Introduction of Broadband Access:  Introduction of Broadband Access In Taiwan, Broadband Access service is usually considered a Type-I services (facility-based), a Type-I operator license from DGT is required. But Users often mix it with ISPs. “Fixed Network services” ( 固定網路業務) ADSL(Asymmetrical Digital Subscriber Loop) Cable Modem LMDS(Local Multi-point Distribution System) or WLAN Fiber in the Loop(Fiber to the Curb, Fiber to the Home) Ethernet/Fast Ethernet/Gigabit Ethernet Introduction of Broadband Access:  Introduction of Broadband Access The equipment of Broadband Access: Usually with one set of terminating equipment or multiplexer at the cerntral office (CO)(局端), or a remote concentration site. The CO equipment must provide WAN data service interconnection. A remote unit is required at the CPE side(用戶端), connected to a PC, SOHO(small office/home office) router, a set-top-box, etc. Introduction of Broadband Access:  Introduction of Broadband Access Introduction to Digital Subscriber Loop(xDSL):  Introduction to Digital Subscriber Loop(xDSL) May use exiting telephone local subscriber loop(用戶迴路 ) as the physical medium. When deployed, require replacement of (modem) equipment of two ends of the loop. Local Loop Unbundling (用戶迴路細分化) or lease of local loop is possible. The copper loop is not replaced. But the loop conditions may vary in noise, cross talk, attenuation, length, etc. The loop condition, the required data rate, and the equipment determine throughput of xDSL. Introduction to Digital Subscriber Loop(xDSL):  Introduction to Digital Subscriber Loop(xDSL) Why rates are different ? Depending on how the spectrum is allocated (symmetric or asymmetric) With longer loop, there will be more noise, more serious attenuation, smaller signal. To maintain high data rate usually require higher signal to noise (S/N) ratio. Various xDSLs are designed for different loop conditions and data rate requirements. Spectrum interference is an issue. Introduction to Digital Subscriber Loop(xDSL):  Introduction to Digital Subscriber Loop(xDSL) What is crosstalk ? Received signal from speakers on another loop, from either near side or remote side. Voice is less sensitive to crosstalk Data at high frequency is sensitive. The amount of crosstalk can determine whether the loops are ready for use in parallel. xDSL Characteristics Comparison:  xDSL Characteristics Comparison DSL flavors:  DSL flavors ONU:Optical Network Unit HDSL(High bit rate DSL):  HDSL(High bit rate DSL) A better way of transmitting T1 or E1 over twisted pair copper lines . Less bandwidth usage Require no repeaters Without the need for bridged-tap removal Less cost Using two pairs for T1(1.544Mbps) and three pairs for E1(2.048Mbps). Typical applications include PBX network connections, cellular antenna stations, digital loop carrier systems, inter-exchange POP(Point of Presence), Internet servers, and private data networks. ADSL(Asymmetric DSL):  ADSL(Asymmetric DSL) The reason for “Asymmetric” has less to do with transmission technology than with the cable plant itself. Many residential applications for digital subscriber services are asymmetric Video on demand, home shopping, Internet access, remote LAN access, multimedia access, specialized PC services. To create multiple channels, ADSL modems divide the available bandwidth of a telephone line in one of two ways: ADSL reference model:  ADSL reference model WAN Interface (ATM, Frame Relay, etc. ) POTS Signal Copper loop Splitter (or remote DSLAM) High Pass Signal Slide14:  xDSL協定架構圖 Cell Switch PC ATU-R DSLAM ATM Network Server Standards of ADSL:  Standards of ADSL Full Rate ADSL: G.DMT (ITU G.992.1Annex A) DMT: discrete multitone Up link up to 864kbps, downlink up to 8 Mbps G.Lite ADSL (ITU G.992.2 Annex A) Up link 512kbps, down link up to 1.5 Mbps VDSL(Very high bit rate DSL):  VDSL(Very high bit rate DSL) FTTH is still prohibitively expensive in a marketplace, so use FTTN instead. One of the enabling technologies for FTTN is VDSL. VDSL technology resembles ADSL to a large degree, but much less complex because of shorter distances. Downstream rates (depending on quality of product and line) 12.96~13.8 Mbps up to 4500 ft 25.92~27.6 Mbps up to 3000 ft 51.84~55.2 Mbps up to 1000 ft Slide17:  xDSL網路電話服務架構 With VoIP The Future of xDSL:  The Future of xDSL Toward Adaptive Rate ADSL Toward multi-service platform for DSLAM: Why not allow ADSL, LAN, n x 64kbps circuit to share a common platform ? Provide QoS control, reduce bandwidth conflict, protect well-behaved-users from mis-behaved users. Competition with Cable Modem Access will continue The real challenge is from the competition of Fast Ethernet or Gigabit Ethernet Access in Metropolitan Area

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