Asymmetric Digital Subsciber Line

ASYMMETRIC DIGITAL SUBSCIBER LINE (ADSL)

JOSHI.U.L,RTTC,TVPM-40

Broadband- Wireline Technologies  Digital Subscriber Line (DSL)  Cable Modem

(Cable TV Network)  Power Line Communications (PLC)

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DSL The copper wires have lots of room for carrying more than your phone conversations -- they are capable of handling a much greater bandwidth, or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to carry conversations 07/29/09 06:34

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DSL Technology  DSL may offer more than 100 times the

network performance of a traditional analog modem  Precise speed of a connection depends upon the type of DSL employed  DSL uses the same telephone line as traditional modem  DSL remains always-on all the time 

Customer no longer need to physically dial up to the ISP to “log in to the internet”

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Advantages of DSL : •You can leave your Internet connection open and still use the phone line for voice calls. •The speed is much higher than a regular modem (1.5 Mbps vs. 56 Kbps) •DSL doesn't necessarily require new wiring; it can use the phone line you already have. •The company that offers DSL will usually provide the modem as part of the installation. 07/29/09 06:34

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Disadvantages : •A DSL connection works better when you are closer to the provider's central office. •The connection is faster for receiving data than it is for sending data over the Internet. •The service is not available everywhere.

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Introduction - History of DSL

1962

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Se rv AT DN ic &T e de in ve tro lo pm du c en Fi es be t DS r-O L pt ic Be tri llc al s or in e th in e tro AN U. du SI S. ce ap s pr AD ov IT SL es UAD co T nc ra SL tif ep DM ie t IT s T G Ust .9 T an 9 ra 2 da . tif 2 rd sp ie s e G c. .9 92 .1 sp ec .

Historic Timeline

1968

1974

1975

1987

1996

1998

1999

The proposal was for the useBell of an asymetrical connection todeveloped deliver heavy downstream video on Thirteen years later (1988) AT&T installs first transatlantic fiber-optic cable and the Bellcore, better known as Labs, developed the ADSL concept 1987, Work began on the B-ISDN model with ATM and Frame-Relay based onstandard DSL concepts The International Telecommunication Union, ITU, then aindraft INTELSAT implements the world's first international digital voice communications A pulse based signal on a dedicated leased line offering faster transfer that analog bsed number of Internet hosts exceeds 100,000. Held upwhich byupstream the slow speed offor SS6 (ISDN USER PARTcalled )to compete with cable companies demand and volume transactions (Pay Movies) service was thelow first public DSL offering systems in 1998 to ADSL world implementation which subsequently ratified ANSI in the United States. in 1998was to standardize standardize ADSL for by world implementation called G-Lite G-Lite 07/29/09 06:34

Digital Subscriber Line

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Introduction - History of DSL DSL Family of Technologies xDSL VDSL Asymmetric

Very High Speed

ADSL SDSL HDSL

G.DMT

High Speed

Full Rate

HDSL-2

Single Pair

High Speed Single Pair

G.Lite 07/29/09 06:34

Limited Rate

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xDSL Family Tree 

xDSL 

Symmetric DSL • Provide identical data rates upstream & downstream



Asymmetric DSL • Provide relatively lower rates upstream but higher rates downstream



Four main variations of xDSL exist:  HDSL-High bit/data rate Digital Sub: Line  SDSL- Symmetric Digital Sub: Line  ADSL-Asymmetrical Digital Sub: Line  VDSL-Very-high-data-rate Digital Sub: Line

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HDSL     

High bit/data rate DSL Can be viewed as equivalent of PCM stream Offers the same bandwidth both upstream and downstream Can work up to a distance of 3.66 to 4.57 kms depending upon the speed required Can deliver 2048 kbps  

On 2 phone lines, each line carrying 1168 kbps On 3 phone lines, each line carrying 784 kbps

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HDSL  No provision exists for voice because it

uses the voice band  HDSL-2 is proposed as next generation HDSL over single phone line 

Requires more aggressive modulation, shorter distance and better phone line

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SDSL      

Symmetric Digital Subscriber Line Rate adaptive version of HDSL Does not support analog calls Works up to 3.7 kms on 0.5 mm dia cable Affordable alternative to dedicated leased lines SHDSL-Symmetric High-bit-rate Digital Subscriber Line is an further improvement over HDSL/SDSL and uses single phone line

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ADSL  



Asymmetric Digital Subscriber Line Used for applications which require greater download bandwidth but require relatively little in opposite direction like Web browsing; File downloads An ADSL circuit connects an ADSL modem on each end of a twisted pair telephone line creating three information channels

A high speed downstream channel  A medium speed duplex channel  A basic telephone service channel 07/29/09 06:34 

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ADSL    



The basic telephone service channel is split off from the digital modem by splitter at client site Allows simultaneous access to the line by the telephone and the computer In case of power/ADSL failure, data transmission is lost but basic telephone service will be operational Provides  16-640 kbps upstream  1.5-9 mbps downstream Can work up to a distance of 3.7 to 5.5 kms depending upon the speed required

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ADSL  Data Rate - Wire Size – Distance Data Rate

Wire Size

Distance

1.5-2.0 Mbps

0.5 mm

18000 Feet

5.5 Kms

1.5-2.0 Mbps

0.4 mm

15000 Feet

4.6 Kms

6.1 Mbps

0.5 mm

12000 Feet

3.7 Kms

6.1 Mbps

0.4 mm

9000 Feet

2.7 Kms

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ADSL Standards: There are two competing and incompatible Modulation standards for ADSL . Discrete MultiTone (DMT): The official ANSI standard for ADSL.

Carrier less Amplitude/Phase (CAP) system :An earlier and more easily implemented standard, which was used on many of the early installations of ADSL

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Whatever the modulation technique used, whenever the same two wires in a pair is used for full – duplex transmission either • the frequency range must be split into Upstream and Downstream bandwidth (FDM) OR •

Echo Cancellation

Must be used 07/29/09 06:34

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ADSL: FDM/Echo Cancellation Upstream

Downstream

Basic Telephone Service

FDM Frequency

Upstream Downstream Basic Telephone Service

Echo Cancellation Frequency

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Echo Canceling and DSLs When the same frequency range is used in both directions, signal reflection could easily be mistaken as a signal originating at the remote end. Echo cancellers electronically subtract the signal sent from the signal received, allowing the signal actually sent from the remote end to be distinguished more easily. In FDM no Echo Control is needed in the end devices.

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Quadrature Amplitude Modulation QAM Bit value Amplitude Phase shift

0

315

Amplitude

001

111 000

101

270

45

90

Phase Shift

000

1

45

001

2

45

010

-1

135

011

-2

135

100

-1

225

101

-2

225

110

1

315

111

2

315

010 100

225 07/29/09 06:34

011

100

135 180

20

QAM To encode a bit stream:

Bit value Amplitude Phase shift 000

1

45

001

2

45

010

-1

135

011

-2

135

001-010-100-011-101-000-011-110 100

-1

225

101

-2

225

110

1

315

111

2

315

001010100011101000011110 break it up into 3-bit triads:

2

0

-2

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t1

t2

t3

t4

t5 21

CAP Upstream /Downstream 2

0

-2

t1

t2

t3

t4

t5

Carrier less AM/PM, a version of suppressed carrier QAM 07/29/09 06:34

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DMT Modulation

No of Bits

256 frequency bands of sub-carriers of 4 KHz bandwidth and spacing of 4.3 KHz. Each sub carrier can support maximum 15 no of bit. Depending on signal to noise Ratio for that sub carrier a decision is taken How many bits that particular sub carrier can Support.

Voice

15

0

Upstream

4 25

Downstream

138 139

1100

Frequency (KHz) 07/29/09 06:34

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What is Discrete Multi-Tone (DMT)

Split the available bandwidth into a large number of subchannels.

Amplitud e Frequency

Bridge taps and also the interference of an AM radio station.

Any other transmission media such as Cable and Wireless

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DMT Processor: Modulation/demodulation 4.3125 kHz

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Discrete Multitone line

coding techniques use multiple carriers, or sub-channels, to transfer data to the farend

Sub-carriers (n)

Fig. 1

6 7

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Sub-carriers (n)

Fig. 2

27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Sub-carriers Fig. 3

255

25

DMT Processor: Modulation/demodulation 4.3125 kHz

These sub-channels are

4.3125 kHz wide (fig. 1) and occupies the following frequencies:  26 kHz to 1.104 MHz . • 249 downstream channels (ATU_C to ATU_R).  26 kHz to 138 kHz. • 25 upstream channels 07/29/09(ATU_R 06:34 to ATU_C).

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Sub-carriers (n)

Sub-carriers (n)

Fig. 1

6 7

Fig. 2

27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Sub-carriers Fig. 3

255

26

Theoretical Maximum Data Rates 4.3125 kHz

 4000 symbols per second are

transmitted.  Maximum of 15 Bits for each subcarrier.  Downstream subcarriers.  248 subcarriers carry data.  Subcarrier 64 is the pilot tone.  Upstream subcarriers.  24 subcarriers carry data.  Subcarrier 16 is the pilot tone.  4000 x 15 x 248 = 14.88 Mbps downstream. 07/29/09 06:34



15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Sub-carriers (n)

Sub-carriers (n)

Fig. 1

6 7

Fig. 2

27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Sub-carriers Fig. 3

255

27

ADSL Architecture

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POTS Splitter •Enables the carriage of analog telephone service and digital data on the same line •It is a low pass filter that seperates analog voice from ADSL frequencies.

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DSLAM: DSL Access Multiplexer •Houses a set of ATU-C interfaces. •Multiplex traffic from multiple ATU-Cs on to a single, high speed trunk to the transport network. •Demultiplex traffic from the transport network and assigns it to the correct ATU-C •Negotiate line speed.

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LINE QUALIFICATION •THE MAXIMUM LOOP RESISTANCE BETWEEN COT AND RT SHALL BE LESS THAN 900 OHMS •THERE SHALL NOT BE ANY LOADING COILS IN THE LINE THE INSULATION OF THE CABLE PAIR SHALL BE GREATER THAN 800 kilo OHM WHEN TESTED WITH 500V MEGGER. The maximum attenuation in the cable pair shall not exceed 20 dB at 150 KHz.

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What are the benefits of ADSL? Fast downloads At least 4.5 times and upto 35 times faster than dial-up connection Always on connection Telephone and Internet access can be used together No telephone call charges for internet surfing Cost effective way to access Internet •

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What kind of PC do I need to run ADSL? Most present day configurations will run ADSL. The following minimum is, however, recommended : 1.Processor 200 MHz (or better) 2.Operating System Windows 98SE (or higher) 3.RAM (memory) 32 MB RAM 4.Free Disk Space 125MB 5.SVGA monitor CD-ROM Drive 6.Network Interface Card(NIC) with Ethernet port with RJ45 socket

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VDSL  Very-high Data-rate DSL  Originally named VADSL (A –Asymmetric)

but was later extended to support both symmetric & asymmetric  Requires one phone line  Supports voice & data  Works between 0.3-1.37 kms depending on speed 07/29/09 06:34

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VDSL  Upstream

data rate of 1.6-2.3 mbps  Downstream data rate of 13-52 mbps  Data Rate - Wire Size – Distance Downstream

Upstream

Distance

12.96 Mbps

1.6-2.3 mbps

4500 Feet

1.37 Kms

25.82 Mbps

1.6-2.3 mbps

3000 Feet

0.91 Kms

51.84 Mbps

1.6-2.3 mbps

1000 Feet

0.30 Kms

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THANK YOU

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