1/6 ADSL Surasak Sanguanpong nguan@ku.ac.th http://www.cpe.ku.ac.th/~nguan Last updated: 9 Feb 2001 Applied Network Research Group Department of Computer Engineering, Kasetsart University 2/6 What is ADSL? ADSL stands for Asymmetric Digital Subscriber Line � ADSL is a new, super high-speed modem technology that � provides data services, such as Internet access, over the existing telephone lines Upstream : 64 Kbps to 1 Mbps PC ADSL ADSL Internet Downstream : 1.5 – 9.0 Mbps Example Speed offers : � � 384 Kbps downstream /128 Kbps upstream for general telecommuters � 1.5 Mbps downstream / 384 Kbps upstream for small offices Applied Network Research Group Department of Computer Engineering, Kasetsart University
3/6 ADSL � High speed communications over twisted pair. � Originally standardized in ANSI T1 in 1993. Concurrent with plain Telephone and ADSL service � can be used simultaneously old telephone service (POTS) Is always terminated at � ADSL Modem the central office (CO). CO Applied Network Research Group Department of Computer Engineering, Kasetsart University 4/6 Modem and ADSL Line card filters determine bandwidth PC Server modem modem 4 KHz Voice Channel Data limited to 33.6 Kbps Local loop determines bandwidth PC Server ADSL ADSL <1 MHz bandwidth data rate up to 52 Mbps depend on distance Applied Network Research Group Department of Computer Engineering, Kasetsart University
5/6 Typical ADSL System Configuration � ??? User Telco Central Office Telco Backbone Class 5 Switch POTS POTS Splitter Splitter PSTN DLSAM ATU-C ATM ATU-R Internet ATU-C ATU-C DSLAM — Digital Subscriber Line Access Multiplexer. A concentrating platform for DSL modems � ATU-C — ADSL transmission unit in CO. It refers to ADSL modems housed in DSLAMs. � ATU-R — ADSL transmission unit in remote (customer) locations. It refers to ADSL CPE. � Applied Network Research Group Department of Computer Engineering, Kasetsart University 6/6 Typical ADSL Network � ??? Radius Server Internet ATM ATU-R PC Router DLSAM PPP Connection Applied Network Research Group Department of Computer Engineering, Kasetsart University
7/6 xDSL Family 1.544/2.048 Mbps symmetric HDSL HDSL two twisted-pair wires to achieve full duplex High bit rate Digital Subscriber Line 1.544/2.048 Mbps symmetric single line version SDSL SDSL of HDSL, echo cancellation is employed Single Data line Digital Subscriber Line DSL 1.5 – 9.0 Mbps , asymmetric ADSL ADSL Single line over POTS Asymmetric Digital Subscriber Line Current View 13 – 52 Mbps , asymmetric VDSL ( A very fast version of ADSL for short length ) VDSL Very High Bit Rate Digital Subscriber Line ADSL based technology with different data rate RADSL RADSL depending on the type communications Rate Adaptive Asymmetric Digital Subscriber Line Applied Network Research Group Department of Computer Engineering, Kasetsart University 8/6 Speed shrinks with distance ADSL has a range of downstream speeds � 50 achievable depending on the distance and wire gauge. 40 VDSL Dominant impairment — Attenuation Attenuation increases with distance and frequency ADSL Secondary impairments — Cross Talk , Impulse noise , Bridged Taps 30 20 10 3 6 9 12 15 18 Distance in kft of 24 (.5 mm) ga wire Applied Network Research Group Department of Computer Engineering, Kasetsart University
9/6 ADSL Spectrum bandwidth is split into three information channels: � � high-speed downstream channel, � medium-speed duplex (upstream) channel � conventional voice channel POTS Upstream Downstream 1.104 4 MHz kHz Upstream utilizes lower Downstream uses as Only 0-4 Khz frequencies to take much of the remaining advantage of reduced near is used for POTS bandwidth as it can end cross talk (NEXT) at CO Applied Network Research Group Department of Computer Engineering, Kasetsart University 10/6 Echo-Cancelled ADSL � ADSL can be used in either an echo-cancellation (EC) or frequency division multiplexing (FDM) POTS Upstream Downstream Less useable downstream bandwidth but more simpler implementation Upstream Downstream POTS More of downstream bandwidth is in the higher quality part of the spectrum Applied Network Research Group Department of Computer Engineering, Kasetsart University
11/6 Bands for ADSL � ADSL uses Discrete Multitone DMT signaling in up- and downstream Consists of up to 256 4.3125 KHz channels, each containing � a QAM modem (each QAM modem has a 4 KHz symbol rate) Upstream Downstream (25 channels) (224 channels) 31 32 256 1 2 3 4 5 6 7 POTS 4.135 133.68 1.104 25.875 Applied Network Research Group Department of Computer Engineering, Kasetsart University 12/6 Compute ADSL Bit Rate � For each 4 KHz channel, max rate is equal to 4 Khz*15=60 Kbps Upstream Downstream POTS Upstream : 25 channels Downstream : 224 channels Bit rate = 224*60 Kbps=13.44 Mbps � Bit rate = 25*60 Kbps=1.5 Mbps � Practical use : 500Kbps to 8 Mbps � Practical use : 64Kbps to 1 Mbps � Applied Network Research Group Department of Computer Engineering, Kasetsart University
13/6 Bits per Channel Allocation � SNR can be continuously monitored and have the bit loading table adjusted # of bits # of bits per Hertz per Hertz 1415 14 13 11 8 f f f Output Frequency response Input Bit rate = 4KHz*(14+15+14+13+11+8) =300 KHz Applied Network Research Group Department of Computer Engineering, Kasetsart University 14/6 DMT Tra DMT with N channels Bit 1 QAM Bit 2 N bits Data QAM Bit N QAM � QAM modulation with 0-15 bits per baud per Hertz Applied Network Research Group Department of Computer Engineering, Kasetsart University
15/6 Splitterless ADSL � Splitterless DSL, a subset of ADSL service. � No splitter, hence low cost and easy to install � G.992.2 standard, also known as G.Lite standard Class 5 Switch No Splitter POTS Splitter PSTN DLSAM ATU-C ATU-R ATM ATU-C ATU-C Applied Network Research Group Department of Computer Engineering, Kasetsart University 16/6 G.lite Spectrum � G.Lite technical aspects � Utilizes only up to 577.875KHz (98 channels) � Each bin limited to 8 bits per symbol � Max data rate = 4KHz*8*98=3.136 Mbps � Practical use : 1.5 Mbps/ 128 Kbps POTS Upstream Downstream G.DMT G.DMT G.lite G.lite 1104.0 133.6875 577.8750 Applied Network Research Group Department of Computer Engineering, Kasetsart University
17/6 Problem of Splittlerless Applied Network Research Group Department of Computer Engineering, Kasetsart University 18/6 Microfilter Applied Network Research Group Department of Computer Engineering, Kasetsart University
19/6 ITU Study Group 15 Standards Activities A full-rate (6 to 8 Mbps) ADSL standard based on G.dmt G.dmt ANSI T1.413 Issue 2 A sub-rate (384 Kbps to 1.5 Mbps) ADSL standard G.lite G.lite which typically will require no splitter An HDSL standard based on ANSI and ETSI G.hdsl G.hdsl standards ITU Study Group 15 A handshaking standard, describe the start-up G.hs G.hs protocol and signaling for identification of xDSL capabilities and negotiation of the operating modes A standard which will identify the requirements for a G.oam G.oam control channel for operations and maintenance for xDSL modems A standard which will define a network model and G.test G.test procedures for testing xDSL modems Applied Network Research Group Department of Computer Engineering, Kasetsart University
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