adsl basic
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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 over60% market share
ADSL is now available in every region of the world
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What does ADSL mean
Asymmetric - The data can flow faster in one directionthan the other. Data transmission has faster downstreamto the subscriber than upstream
Digital - No type of communication is transferred in ananalog method. All data is purely digital, and only at theend, modulated to be carried over the line.
SubscriberLine - The data is carried over a single twistedpair copper loop to the subscriber premises
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ADSL standards :ADSL standards :
Standard nameStandard name Common nameCommon name DownstreamDownstream
raterate
UpstreamUpstream
raterate
ITU G.992.1ITU G.992.1 ADSL (G.DMT) ADSL (G.DMT) 8 Mbit/s8 Mbit/s 1.0 Mbit/s1.0 Mbit/s
ITU G.992.2ITU G.992.2 ADSL Lite (G.Lite)ADSL Lite (G.Lite) 1.5 Mbit/s1.5 Mbit/s 0.5 Mbit/s0.5 Mbit/sITU G.992.3/4ITU G.992.3/4 ADSL2 ADSL2 12 Mbit/s12 Mbit/s 1.0 Mbit/s1.0 Mbit/s
ITU G.992.3/4 Annex JITU G.992.3/4 Annex J ADSL2 ADSL2 12 Mbit/s12 Mbit/s 3.5 Mbit/s3.5 Mbit/s
ITU G.992.3/4 Annex LITU G.992.3/4 Annex L RERE--ADSL2 ADSL2 5 Mbit/s5 Mbit/s 0.8 Mbit/s0.8 Mbit/s
ITU G.992.5ITU G.992.5 ADSL2+ ADSL2+ 24 Mbit/s24 Mbit/s 1.0 Mbit/s1.0 Mbit/s
ITU G.992.5 Annex LITU G.992.5 Annex L RERE--ADSL2+ ADSL2+ 24 Mbit/s24 Mbit/s 1.0 Mbit/s1.0 Mbit/s
ITU G.992.5 Annex MITU G.992.5 Annex M ADSL2+ ADSL2+ 28 Mbit/s28 Mbit/s 3.5 Mbit/s3.5 Mbit/s
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ISDN
ADSL
FTTx,
VDSL2,
ADSL2plus
Enhanced
Copper
Hybrid Fibre/Copper
Pure Fibre
ADSLSpeed Comparison
Voice band
Modem
FTTH
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ADSL Range
In general, the maximum range for DSL without a repeateris 5.5 km
As distance decreases toward the telephone companyoffice, the data rate increases
For larger distances, you may be able to have DSL if yourphone 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 km1.5 or 2 Mbps 26 AWG 0.4 mm 2.7
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ADSLSpeed 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.
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ADSL network components
The ADSL modem at the customer premises(ATU-R)
The modem of the central office (ATU-C)
DSL access multiplexed (DSLAM)
Broadband Access Server (BAS)
Splitter - an electronic low pass filter that separates the
analogue voice orISDN signal from ADSL data
frequencies DSLAM.
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ADSLLoopArchitecture
ISP
Central Office Subscriber premises
Voice Switch
DSL
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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
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How does ADSL work ADSL exploits theADSL exploits the unused analogue bandwidthunused analogue bandwidth
available in the wiresavailable in the wires
ADSL works by using a frequency splitter device to split aADSL 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
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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 formodulating the ADSL signal:
Carrier less Amplitude Phase (CAP)
Discrete Multi-Tone (DMT)
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Carrierless Amplitude Phase
Carrier less Amplitude Phase (CAP) is an encodingCarrier less 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 isThe 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 inThe 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 toThese channels are widely separated in order tominimize the possibility of interference between theminimize the possibility of interference between the
channels.channels.
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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 channelsto ensure that the best channels are used for transmission
and reception.
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The DMT frequency bands
Frequency Division Multiplexing (FDM)
Echo Cancellation
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Asynchronous Transfer ModeAsynchronous Transfer Mode
ATM is a connectionATM is a connection--orientated techniqueorientated technique
ATM provides cell sequence integrityATM provides cell sequence integrity
Cells are much smaller than standard packetCells are much smaller than standard packet--switchedswitched
networks (53 bytes)networks (53 bytes)
The quality of transmission links has lead to the omissionThe quality of transmission links has lead to the omission
of overheadsof overheads
There is no space between cellsThere is no space between cells
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Types ofATM 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)
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ATM Layer
The ATM layer transport information across the networkThe 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 PathThe Virtual Path
This mechanism is used to provide quality of service (QoS)This mechanism is used to provide quality of service (QoS)
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ATM Connections
The connection between two endpoints is called a VirtualThe connection between two endpoints is called a Virtual
Channel (VC).Channel (VC).
A Virtual Path (VP) is a term for a bundle of virtualA 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 addressingVirtual paths are used to simplify the ATM addressing
structure.structure.
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ATM Adaptation Layer (AAL)
The ATM Adaptation Layer (AAL) converts informationThe 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
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ADSL Protocol stacks
Ethernet overEthernet over
ATM (EoA)ATM (EoA)
IP over ATMIP over ATM
(IPoA)(IPoA)
PPP over ATMPPP over ATM
(PPPoA)(PPPoA)
PPP overEthernetPPP overEthernet
(PPPoE)(PPPoE)
Native ATMNative ATM
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PointPoint--toto--Point Protocol overPoint Protocol over
Ethernet overATM (PPPoEoA)Ethernet overATM (PPPoEoA)
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Conclusion: Pros & Cons
Why ADSL?Why ADSL? Simultaneous Internet and voice/fax capabilities overSimultaneous Internet and voice/fax capabilities over
a single telephone linea single telephone line
Uninterrupted, highUninterrupted, high--speed Internet access that'sspeed Internet access that's
always onalways on--lineline CostCost--effective solution for societyeffective solution for society
Data Security that exceeds other technologiesData Security that exceeds other technologies
Fast download speedsFast download speeds
ADSL disadvantages:ADSL disadvantages: DistanceDistance--sensitivesensitive
Slower upload speedsSlower upload speeds
Phone line requiredPhone line required
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Thank You For YourAttention
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