adsl

ADSLADSLAsymmetric Digital Subscriber Line Asymmetric Digital Subscriber Line

Introduction

• 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 50 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

What does ADSL mean

• 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

ADSL standards :ADSL standards :

Standard name Standard name Common name Common name Downstream Downstream rate  rate 

Upstream Upstream rate rate

ITU G.992.1 ITU G.992.1 ADSL (G.DMT) ADSL (G.DMT) 8 Mbit/s 8 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.2 ITU G.992.2 ADSL Lite (G.Lite) ADSL Lite (G.Lite) 1.5 Mbit/s 1.5 Mbit/s 0.5 Mbit/s 0.5 Mbit/s

ITU G.992.3/4 ITU G.992.3/4 ADSL2 ADSL2 12 Mbit/s 12 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.3/4 Annex J ITU G.992.3/4 Annex J ADSL2 ADSL2 12 Mbit/s 12 Mbit/s 3.5 Mbit/s 3.5 Mbit/s

ITU G.992.3/4 Annex LITU G.992.3/4 Annex L RE-ADSL2 RE-ADSL2 5 Mbit/s 5 Mbit/s 0.8 Mbit/s 0.8 Mbit/s

ITU G.992.5 ITU G.992.5 ADSL2+ ADSL2+ 24 Mbit/s 24 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.5 Annex LITU G.992.5 Annex L RE-ADSL2+ RE-ADSL2+ 24 Mbit/s 24 Mbit/s 1.0 Mbit/s 1.0 Mbit/s

ITU G.992.5 Annex M ITU G.992.5 Annex M ADSL2+ ADSL2+ 28 Mbit/s 28 Mbit/s 3.5 Mbit/s 3.5 Mbit/s

ISDN

ADSL

FTTx, VDSL2,ADSL2plus

EnhancedCopper

Hybrid Fibre/Copper

Pure Fibre

ADSL Speed Comparison

Voice bandModem

FTTH

ADSL Range• 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

• For larger distances, you may be able to have DSL if your phone company has extended the local loop with optical fiber cable

Data Rate Wire gauge Wire size Distance

1.5 or 2 Mbps 24 AWG 0.5 mm 5.5 km

1.5 or 2 Mbps 26 AWG 0.4 mm 4.6 km

6.1 Mbps 24 AWG 0.5 mm 3.7 km

1.5 or 2 Mbps 26 AWG 0.4 mm 2.7

ADSL Speed Factors

• 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.

ADSL network components

• The ADSL modem at the customer premises(ATU-R)

• The modem of the central office (ATU-C)

• DSL access multiplexer (DSLAM)

• Broadband Access Server (BAS)

• Splitter - an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM.

ADSL Loop Architecture

ISP

Central Office Subscriber premises

Voice Switch

DSL

ADSL Requirements

• Phone-line, activated by your phone company for ADSL

• Filter to separate the phone signal from the Internet signal

• ADSL modem

• Subscription with an ISP supporting ADSL

How does ADSL work• ADSL exploits the ADSL exploits the unused analogue bandwidth unused analogue bandwidth

available in the wiresavailable in the wires

• ADSL works by using a frequency splitter device to split a ADSL works by using a frequency splitter device to split a traditional voice telephone line into two frequenciestraditional voice telephone line into two frequencies

4 25,875 138 1104 KHz

PSTNPSTN DownstreamDownstreamUpstreamUpstream

ADSL Modulation

• 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)

Carrierless Amplitude Phase• Carrierless Amplitude Phase (CAP) is an encoding Carrierless Amplitude Phase (CAP) is an encoding

method that divides the signals into two distinct bands:method that divides the signals into two distinct bands:

1.1. The upstream data channel (to the service provider), which is The upstream data channel (to the service provider), which is carried in the band between 25 and 160kHzcarried in the band between 25 and 160kHz

1.1. The downstream data channel (to the user), which is carried in The downstream data channel (to the user), which is carried in the band from 200kHz to 1.1MHz .the band from 200kHz to 1.1MHz .

• These channels are widely separated in order to These channels are widely separated in order to minimize the possibility of interference between the minimize the possibility of interference between the channels.channels.

Discrete Multi-tone (DMT)

• Discrete Multi-Tone (DMT) separates the DSL signal so that the usable frequency range is separated into 256 channels of 4.3125kHz 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.

The DMT frequency bands• Frequency Division Multiplexing (FDM)

• Echo Cancellation

Asynchronous Transfer ModeAsynchronous Transfer Mode

• ATM is a connection-orientated technique ATM is a connection-orientated technique

• ATM provides cell sequence integrity ATM provides cell sequence integrity

• Cells are much smaller than standard packet-switched Cells are much smaller than standard packet-switched networks (53 bytes)networks (53 bytes)

• The quality of transmission links has lead to the omission The quality of transmission links has lead to the omission of overheads of overheads

• There is no space between cells There is no space between cells

Types of ATM services

• Constant Bit Rate (CBR)Constant Bit Rate (CBR)

• Variable Bit Rate (VBR)Variable Bit Rate (VBR)

• Unspecified Bit Rate (UBR)Unspecified Bit Rate (UBR)

• Available Bit Rate (ABR)Available Bit Rate (ABR)

ATM Layer

• The ATM layer transport information across the network The ATM layer transport information across the network

• ATM uses virtual connections for the information transportATM uses virtual connections for the information transport

• The connections are divided into two levels: The connections are divided into two levels:

– The Virtual ChannelsThe Virtual Channels

– The Virtual Path The Virtual Path

• This mechanism is used to provide quality of service (QoS)This mechanism is used to provide quality of service (QoS)

ATM Connections

• The connection between two endpoints is called a Virtual The connection between two endpoints is called a Virtual Channel (VC).Channel (VC).

• A Virtual Path (VP) is a term for a bundle of virtual A Virtual Path (VP) is a term for a bundle of virtual channel links that all have the same endpoints.channel links that all have the same endpoints.

• Each VC and VP has a unique identifierEach VC and VP has a unique identifier

• Virtual paths are used to simplify the ATM addressing Virtual paths are used to simplify the ATM addressing structure.structure.

ATM Adaptation Layer (AAL)

• The ATM Adaptation Layer (AAL) converts information The ATM Adaptation Layer (AAL) converts information from the upper layers into ATM cellsfrom the upper layers into ATM cells

• The standard used for ATM over ADSL services is AAL5The standard used for ATM over ADSL services is AAL5

• AAL5 Encapsulation MethodsAAL5 Encapsulation Methods

– Virtual Channel Multiplexing (VCMux)Virtual Channel Multiplexing (VCMux)– LLC/SNAPLLC/SNAP

• For detailed information please refer to the RFC 1483For detailed information please refer to the RFC 1483

ADSL Protocol stacks

Ethernet over Ethernet over ATM (EoA)ATM (EoA)

IP over ATM IP over ATM (IPoA)(IPoA)

PPP over ATM PPP over ATM (PPPoA)(PPPoA)

PPP over Ethernet PPP over Ethernet (PPPoE)(PPPoE)

Native ATMNative ATM

Point-to-Point Protocol over Point-to-Point Protocol over Ethernet over ATM (PPPoEoA)Ethernet over ATM (PPPoEoA)

Conclusion: Pros & Cons

• Why ADSL?Why ADSL?• Simultaneous Internet and voice/fax capabilities over a Simultaneous Internet and voice/fax capabilities over a

single telephone line single telephone line • Uninterrupted, high-speed Internet access that's Uninterrupted, high-speed Internet access that's

always on-line always on-line • Cost-effective solution for societyCost-effective solution for society• Data Security that exceeds other technologies Data Security that exceeds other technologies • Fast download speedsFast download speeds

• ADSL disadvantages:ADSL disadvantages:• Distance-sensitiveDistance-sensitive• Slower upload speedsSlower upload speeds• Phone line requiredPhone line required

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