ADSL Raghunath M D BSNL Mobile Services, Ernakulam, Ph:

ADSL: Introduction ADSL ADSL is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines ADSL is capable of providing up to 24 Mbps, and supports voice, video and data. ADSL is the #1 Broadband Choice in the World with over 60% market share ADSL is now available in every region of the world 2

What does ADSL mean ? ADSL Asymmetric - The data can flow faster in one direction than the other. Data transmission has faster downstream to the subscriber than upstream Digital - No type of communication is transferred in an analog method. All data is purely digital, and only at the end, modulated to be carried over the line. Subscriber Line - The data is carried over a single twisted pair copper loop to the subscriber premises 3

ADSL Standards ADSL 4 Standard nameCommon nameDownstream rate Upstream rate ITU G.992.1ADSL (G.DMT)8 Mbit/s1.0 Mbit/s ITU G.992.2ADSL Lite (G.Lite)1.5 Mbit/s0.5 Mbit/s ITU G.992.3/4ADSL212 Mbit/s1.0 Mbit/s ITU G.992.3/4 Annex JADSL212 Mbit/s3.5 Mbit/s ITU G.992.3/4 Annex LRE-ADSL25 Mbit/s0.8 Mbit/s ITU G.992.5ADSL2+24 Mbit/s1.0 Mbit/s ITU G Annex LRE-ADSL2+24 Mbit/s1.0 Mbit/s ITU G Annex MADSL2+28 Mbit/s3.5 Mbit/s

ADSL: Speed Comparison ADSL 5 ISDN ADSL FTTx, VDSL2, ADSL2plus Enhanced Copper Hybrid Fibre/Copper Pure Fibre Voice band Modem FTTH

ADSL Range ADSL In general, the maximum range for DSL without a repeater is 5.5 km As distance decreases toward the telephone company office, the data rate increases 6 Data RateWire gaugeWire sizeDistance 1.5 or 2 Mbps24 AWG0.5 mm5.5 km 1.5 or 2 Mbps26 AWG0.4 mm4.6 km 6.1 Mbps24 AWG0.5 mm3.7 km 1.5 or 2 Mbps26 AWG0.4 mm2.7

ADSL: Speed Factors ADSL The distance from the local exchange The type and thickness of wires used The number and type of joins in the wire The proximity of the wire to other wires carrying ADSL, ISDN and other non-voice signals The proximity of the wires to radio transmitters. 7

ADSL: Network Componenets ADSL The ADSL modem at the customer premises(ATU-R) The modem of the central office (ATU-C) DSL access multiplexer (DSLAM) Broadband Remote Access Server (BRAS) Splitter - an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM. 8

ADSL: Loop Architecture ADSL 9

ADSL: How it works ADSL ADSL exploits the unused analogue bandwidth available in the wires ADSL works by using a frequency splitter device to split a traditional voice telephone line into two frequencies , KHz PSTNDownstreamUpstream

ADSL: Modulation ADSL Modulation is the overlaying of information (or the signal) onto an electronic or optical carrier waveform There are two competing and incompatible standards for modulating the ADSL signal: Carrierless Amplitude Phase (CAP) Discrete Multi-Tone (DMT) 11

ADSL: CAP ADSL Carrierless Amplitude Phase (CAP) is an encoding method that divides the signals into two distinct bands The upstream data channel (to the service provider), which is carried in the band between 25 and 160kHz The downstream data channel (to the user), which is carried in the band from 200kHz to 1.1MHz. These channels are widely separated in order to minimize the possibility of interference between the channels. 12

ADSL: DMT ADSL Discrete Multi-Tone (DMT) separates the DSL signal so that the usable frequency range is separated into 256 channels of kHz each. DMT has 224 downstream frequency bins (or carriers) and 32 upstream frequency bins. DMT constantly shifts signals between different channels to ensure that the best channels are used for transmission and reception. 13

DMT Frequency bands ADSL Frequency Division Multiplexing (FDM) 14

ATM ADSL ATM (Asynchronous Transfer Mode) is a connection- orientated technique ATM provides cell sequence integrity Cells are much smaller than standard packet-switched networks (53 bytes) The quality of transmission links has lead to the omission of overheads There is no space between cells 15

Types of ATM ADSL Constant Bit Rate (CBR) Variable Bit Rate (VBR) Unspecified Bit Rate (UBR) Available Bit Rate (ABR) 16

ATM Connections ADSL The connection between two endpoints is called a Virtual Channel (VC). A Virtual Path (VP) is a term for a bundle of virtual channel links that all have the same endpoints. Each VC and VP has a unique identifier Virtual paths are used to simplify the ATM addressing structure. 17

ATM Adaptation :Layer ADSL The ATM Adaptation Layer (AAL) converts information from the upper layers into ATM cells The standard used for ATM over ADSL services is AAL5 AAL5 Encapsulation Methods Virtual Channel Multiplexing (VCMux) LLC/SNAP (Logical Link Control/SubNetwork Access Protocol) 18

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