“TRENDS IN DSL AND ADSL”

A SEMINAR REPORT

Submitted

In the partial fulfillment of the requirements for the award of the degree of

BACHELOR OF TECHNOLOGY in

ELECTRONICS AND COMMUNICATION ENGINEERING

by G.VARUN KUMAR

(B14EC004)

Under the supervision of Dr.K.ASHOKA REDDY

Professor

Estd.1980

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERINGKAKATIYA INSTITUTE OF TECHNOLOGY & SCIENCE

(An Autonomous Institute Under the Kakatiya University, Warangal)WARANGAL – 506015

2016-2017

KAKATIYA INSTITUTE OF TECHNOLOGY & SCIENCE(An Autonomous Institute Under the Kakatiya University, Warangal)

DEPARTMENT OF ELECTRONICS & COMMUNICATIONENGINEERING

Estd.1980

CERTIFICATE

This is to certify that seminar report entitled “TRENDS IN DSL AND DSL”

embodies the original work done by G.VARUN KUMAR bearing the Roll Number

B41EC004 studying V Semester in partial fulfilment of the requirement for the award

of degree of the Bachelor of Technology in Electronics & Communication

Engineering from KAKATIYA INSTITUTE OF TECHNOLOGY & SCIENCE,

WARANGAL during the academic year 2016-2017.

Supervisor Head of the Department:

Dr.K.ASHOKA REDDY Prof. G.Raghotham Reddy Professor Head, Dept. of ECE

Dept of ECE .KITS ,warangal KITS, Warangal

ACKNOWLEDGEMENT

I would like to express my deep sense of gratitude to my seminar

supervisorDr.K.ASHOKA REDDY Professor, KITS-Warangal, for valuable support in making

the seminar complete in time.

I sincerely thank the Seminar Coordinators, Smt. A.Vijaya, Associate professor, & Sri

A.Pavan, Asst. Professor, Dept. of ECE for timely conduction of seminars.

I heartfully thank Prof. G. Raghotham Reddy, Head & Dept. of ECE for his constant

support and encouragement.

I cordially thank Dr. P.Venkateshwar Rao, Principal, KITS, Warangal, for his kind

gesture and support.

I wish to express my gratitude to Dr. Y.Manohar, Director, KITS, Warangal, for being a

source of strength.

Finally, I thank all those people who are responsible for making this report possible

through meaningful contribution.

(G.VARUN KUMAR)B14EC004

ABSTRACT The past decade has seen extensive growth of the telecommunications industry,with the increased popularity of the Internet and other data communicationservices. While offering the world many more services than were previouslyavailable, they are limited by the fact that they are being used on technologythat was not designed for that purpose.The majority of Internet users accesstheir service via modems connects to the Plain Old Telephone System (POTS).In the early stages of the technology, modems were extremely slow by today'sstandards, but this was not a major issue. A POTS connection provided anadequate medium for the relatively small amounts of data that requiredtransmission, and so was the existing system was the logical choice over specialcabling.Technological advances have seen these rates increase up to a point where theaverage Internet user can now download at rates approaching 50Kbps, and sendat 33.6Kps. However, POTS was designed for voice transmission, at frequenciesbelow 3kHz, and this severely limits the obtainable data rates of the system. Toincrease performance of new online services, such as steaming audio and video,and improve general access speed, the bandwidth hungry public must thereforeconsider other alternatives. Technologies, such as ISDN or cable connections,have been in development for sometime but require special cabling. This makesthem expensive to set up, and therefore not have not been a viable alternativefor most people.The mass deployment of highspeed Digital Subscriber Line (DSL) has changedthe playing field for service providers. DSL, which encompasses severaldifferent technologies, essentially allows the extension of megabit bandwidthcapacities from the service provider central office to the customer premises.Utilizing existing copper cabling, DSL is available at very reasonable costswithout the need for massive infrastructure replacement.Asynchronous Digital Subscriber Line technology, ADSL, is a more recentinnovation which dramatically increases user bandwidth with potential forspeed increase of more than a factor of 50. The major attraction is that it isimplemented using existing twisted pair telephone lines, theoreticallyeliminating the need for installation of special cabling. This makes ADSL amore cost effective, and hence commercially viable, system for wide bandwidthdata transmission.

INDEX

ABSTRACT

LIST OF FIGURES

CHAPTER 1 INTRODUCTION 1-2

1.1DIFFERNT VARIANTS OF DSL

1.2WHAT MAKES DSL POPULAR

1.3WHAT ARE ITS BENEFITS

CHAPTER 2 ASYMMETRIC DIGITAL SUBSCRIBER LINE 3 2.1 ADSL

CHAPTER 3 DSL WORKING 4-83.1 DSL EQUIPMENT3.2 DSL HARDWARE

CHAPTER 4 ADSL TECHNOLOGY 9-124.1ADSL TECHNOLOGY4.2DSL TRANSCEIVER-NETWORK

CHAPTER 5 METHODS TO SPLIT SIGNAL 13-14 5.1 DIFFERENT METHIDS OF SPLITTING SIGNALCHAPTER 6 STANDARDS AND ASSOCIATION 15 6.1 STANDARDSCHAPTER 7 DISTANCE LIMITATION 16

7.1DISTANCE LIMITATIONS OF DSL AND ADSLCHAPTER 8 DSL FUTURE 17CHAPTER 9 APPLICATIONS 18-22 9.1 APPLICATIONS OF DSL AND ADSLCHAPTER 10 CONCLUSION 23 REFFERNCES 24LIST OF FIGURESFIGURE 3.1 SCHEMATIC DIAGRAM OF DSL WORKING 05FIGURE 3.2 BLOCK DIAGRAM OF DSL 08FIGURE 4.1 DIAGRAM OF ADSL COMPONENTS 09FIGURE 4.2 ADSL TRANSCEIVER-NETWORK 10FIGURE 4.3 SCHEMATIC DIAGRAM OF ADSL WORKING 11FIGURE 5.1 DIAGRAM OF CAP 12FIGURE 5.2 DIAGRAM OF DMT 12FIGURE 5.3 DIAGRAM OF LPF 13

FIGURE 9.1 DSL COMPARISION 19FIGURE 9.2 TECHNOLOGY WISE MARKET SHARE OF BROADBANDSHARES 20FIGURE 9.3 DSL TECHNOLOGY IN VARIOUS COUNTRIES 21FIGURE 9.4 PIE CHART OF WIRELESS MARKET 22

CHAPTER-1 INTRODUCTIONThe past decade has seen extensive growth of the telecommunications industry,with the increased popularity of the Internet and other data communicationservices. While offering the world many more services than were previouslyavailable, they are limited by the fact that they are being used on technologythat was not designed for that purpose.The majority of Internet users access their service via modems connects to thePlain Old Telephone System (POTS). In the early stages of the technology,modems were extremely slow by today's standards, but this was not a majorissue. A POTS connection provided an adequate medium for the relatively smallamounts of data that required transmission, and so was the existing system wasthe logical choice over special cabling.Technological advances have seen these rates increase up to a point where theaverage Internet user can now download at rates approaching 50Kbps, and sendat 33.6Kps. However, POTS was designed for voice transmission, at frequenciesbelow 3kHz, and this severely limits the obtainable data rates of the system. Toincrease performance of new online services, such as steaming audio and video,and improve general access speed, the bandwidth hungry public must thereforeconsider other alternatives. Technologies, such as ISDN or cable connections,have been in development for sometime but require special cabling. This makesthem expensive to set up, and therefore have not been a viable alternative formost people

1.1 DIFFERENT VARIANTS OF DSLHDSL is the pioneering high speed format, but is not a commercially viable option due to its need for two twisted pairs and does not have support for normal telephone services.SDSL is symmetric DSL, and operates over a single twisted pair with supportfor standard voice transmission. The problem with this system is that it islimited to relatively short distances and suffers NEXT limitation due to the useof the same frequencies for transmitting and receiving.IDSL stands for ISDN DSL, and is in many ways similar to ISDN technology.It's disadvantages are the lack of support for analog voice, and that its 128kbpsrate is not much greater than that offered by standard 56kbps V90 modems.VDSL provides very high bit rate DSL, up to 52Mbps, but requires shorterconnections lengths than are generally practical. It has been used in conjunctionwith an experimental project, FTTC (Fiber to the Curb), but development in thisarea has slowed due to commercial viability issues.ADSL is the most promising DSL technology, proving suitable for personal broadband requirements and allowing for the same channel to still act as a traditional POTS service. Rate Adaptive DSL, RADSL, is a further

advancement which is able to automatically optimize the ADSL data rate to suit the conditions of the line being used.1.2. WHAT MAKES DSL POPULARDigital Subscriber Line (DSL) technology provides high-speed Internet Access using regular telephone lines. It has the ability to move data over the phone lines typically at speeds from 256K to 1.5Mb - up to 25 times quicker than the fastest analog modems available today (56,000 bits per second).1.3. WHAT ARE THE BENEFITS?DSL is Always On, 24 hrs A DayNo Dial-Up RequiredData SecurityNo Second Phone Line RequiredUse the Phone At The Same Time You Are On-LineNo Dropped ConnectionsSuper Fast SpeedsFlat Rate BillingUpgrade Speed As Your Needs ChangeCost EffectiveThe Bandwidth You Need To Truly Experience The Internet. Inaddition to its very high speed, DSL has many benefits over analog connections.Unlike dial-up connections that require analog modems to "dial-in" to the Internet Service Provider every time the user wants to retrieve e-mail or obtain access to the Internet, DSL connections are always on.

CHAPTER- 2 ASYMMETRIC DIGITAL SUBSCRIBER LINE (ADSL)

2.1 ASYMMETRIC DIGITAL SUBSCRIBER LINE (ADSL)Asymmetric Digital Subscriber Line (ADSL), a modem technology,converts existing twisted-pair telephone lines into access paths for multimediaand high-speed data communications. ADSL can transmit up to 6 Mbps to asubscriber, and as much as 832 kbps or more in both directions. Such ratesexpand existing access capacity by a factor of 50 or more without new cabling.ADSL is literally transforming the existing public information network fromone limited to voice, text and low resolution graphics to a powerful, ubiquitoussystem capable of bringing multimedia, including full motion video, toeveryone's home this century. ADSL will play a crucial role over the next ten or more years as telephonecompanies, and other service providers, enter new markets for deliveringinformation in video and multimedia formats. New broadband cabling will takedecades to reach all prospective subscribers. But success of these new serviceswill depend upon reaching as many subscribers as possible during the first fewyears. By bringing movies, television, video catalogs, remote CD-ROMs,corporate LANs, and the Internet into homes and small businesses, ADSL willmake these markets viable, and profitable, for telephone companies andapplication suppliers alike.Asymmetric Digital Subscriber Line (ADSL) technology is asymmetric. Itallows more bandwidth downstream from an NSP's central office to thecustomer site than upstream from the subscriber to the centraloffice. Thisasymmetry, combined with always-on access (which eliminates call setup),makes ADSL ideal for Internet/intranet surfing, video-ondemand, and remoteLAN access. Users of these applications typically download much moreinformation than they send.ADSL transmits more than 6 Mbps to a subscriber and as much as 640 kbpsmore in both directions (shown in Figure-1). Such rates expand existing accesscapacity by a factor of 50 or more without new cabling. ADSL can literallytransform the existing public information network from one limited to voice,text, and low-resolution graphics to a powerful, ubiquitous system capable ofbringing multimedia, including full-motion video, to every home this century.

CHAPTER 3 DSL WORKING

3.1 DSL EQUIPMENT: DSLAMThe DSLAM at the access provider is the equipment that really allows DSL tohappen. A DSLAM takes connections from many customers and aggregatesthem onto a single, high-capacity connection to the Internet. DSLAMs aregenerally flexible and able to support multiple types of DSL in a single centraloffice, and different varieties of protocol and modulation – both CAP and DMT,for example -- in the same type of DSL. In addition, the DSLAM may provideadditional functions including routing or dynamic IP address assignment for thecustomers.The DSLAM provides one of the main differences between user service throughADSL and through cable modems. Because cable-modem users generally sharea network loop that runs through a neighborhood, adding users means loweringperformance in many instances. ADSL provides a dedicated connection fromeach user back to the DSLAM, meaning that users won't see a performancedecrease as new users are added -- until the total number of users begins tosaturate the single, high-speed connection to the Internet. At that point, anupgrade by the service provider can provide additional performance for all theusers connected to the DSLAM.

FIGURE 3.1 SCHEMATIC DIAGRAM OF DSL WORKING3.1.1 POTS One of the ways that POTS makes the most of the telephone company's wiresand equipment is by limiting the frequencies that the switches, telephones andother equipment will carry. Human voices, speaking in normal conversationaltones, can be carried in a frequency range of 0 to 3,400 Hertz (cycles persecond). This range of frequencies is tiny. The wires themselves have thepotential to handle frequencies up to several million Hertz in most cases.[1] Theuse of such a small portion of the wire's total bandwidth is historical --remember that the telephone system has been in place, using a pair of copperwires to each home, for about a century. By limiting the frequencies carried over

the lines, the telephone system can pack lots of wires into a very small spacewithout worrying about interference between lines. Modern equipment thatsends digital rather than analog data can safely use much more of the telephoneline's capacity. DSL does just that. 3.1.2 Modems POTS connects your home or small business to a telephone company officeover copper wires that are wound around each other and called twisted pair.Traditional phone service was created to let you exchange voice informationwith other phone users and the type of signal used for this kind of transmissionis called an analog signal. An input device such as a phone set takes an acousticsignal (which is a natural analog signal) and converts it into an electricalequivalent in terms of volume (signal amplitude) and pitch (frequency of wavechange). Since the telephone company's signalling is already set up for thisanalog wave transmission, it's easier for it to use that as the way to getinformation back and forth between your telephone and the telephone company.That's why your computer has to have a modem - so that it can demodulate theanalog signal and turn the values into a string of 1s and 0s.[9] This is calleddigital information. Analog modems send their signals through the public switched telephonenetwork, the same one that connects ordinary telephones.[3] ADSL modems"piggyback" their signals on top of the voice signal. On the phone company'spremises, the line gets split - the voice calls are sent to the public switchedtelephone network, and the data transmission goes to the Internet. This methodmoves data off the phone companies' lines and instead uses connectionsoptimized for carrying Internet traffic. 3.1.3 Signal Splitting ADSL works by splitting the phone line into two frequency ranges. Thefrequencies below 4 kHz are reserved for voice, and the range above that is usedfor data. Several modulation technologies are used by various kinds of DSL,although these are being standardized by the International TelecommunicationUnion (ITU). Different DSL modem makers are using either Discrete Multi-Tone Technology (DMT) or Carrier-less Amplitude Modulation (CAP). A thirdtechnology, known as Multiple Virtual Line (MVL), is another possibility. Presented here are the two competing and incompatible standards for ADSL.The official ANSI standard for ADSL is DMT. According to equipmentmanufacturers, most of the ADSL equipment installed today uses DMT. Theearlier and more easily implemented standard was the CAP system, which wasused on many of the early installations of ADSL. While both accomplish thesame result with similar speeds, DMT and CAP are distinctively different indesign and application, and are not compatible with each other. 3.1.4 CAP CAP operates by dividing the signals on the telephone line into three distinctbands: Voice conversations are carried in the 0 to 4 KHz (kilohertz) band, as

they are in all POTS circuits. The upstream channel (from the user back to theserver) is carried in a band between 25 and 160 KHz. The downstream channel(from the server to the user) begins at 240 KHz and goes up to a point thatvaries depending on a number of conditions (line length, line noise, number ofusers in a particular telephone company switch) but has a maximum of about1.5 MHz (megahertz). This system, with the three channels widely separated,minimizes the possibility of interference between the channels on one line, orbetween the signals on different lines.

3.1.5 DMT DMT also divides signals into separate channels, but doesn't use two fairlybroad channels for upstream and downstream data. Instead, DMT divides thedata into 247 separate channels, each 4 KHz wide. One way to think about it isto imagine that the phone company divides your copper line into 247 different4-KHz lines and then attaches a modem to each one. You get the equivalent of247 modems connected to your computer at once! Each channel is monitoredand, if the quality is too impaired, the signal is shifted to another channel. Thissystem constantly shifts signals between different channels, searching for thebest channels for transmission and reception. In addition, some of the lowerchannels (those starting at about 8 KHz), are used as bidirectional channels, forupstream and downstream information. Monitoring and sorting out theinformation on the bidirectional channels, and keeping up with the quality of all247 channels, makes DMT more complex to implement than CAP, but gives itmore flexibility on lines of differing quality. 3.1.6 Low-Pass Filter CAP and DMT are similar in one way that you can see as a DSL user. If youhave ADSL installed, you were almost certainly given small filters to attach tothe outlets that don't provide the signal to your ADSL modem. These filters arelow-pass filters -- simple filters that block all signals above a certain frequency.Since all voice conversations take place below 4 KHz, the low-pass (LP) filtersare built to block everything above 4 KHz, preventing the data signals frominterfering with standard telephone calls. 3.2DSL Hardware/equipment To interconnect multiple DSL users to a high-speed backbone network, thetelephone company uses a Digital Subscriber Line Access Multiplexer(DSLAM). Typically, the DSLAM connects to an asynchronous transfer mode(ATM) network that can aggregate data transmission at gigabit data rates. At theother end of each transmission, a DSLAM de-multiplexes the signals andforwards them to appropriate individual DSL connections. ADSL uses two pieces of equipment, one on the customer end and one at theInternet service provider, Telephone Company or other provider of DSLservices. At thecustomer's location there is a DSL transceiver, which may also

provide other services. The DSL service provider has a DSL Access Multiplexer(DSLAM) to receive customer connections.

FIGURE 3.1.2 BLOCK DIAGRAM OF DSL

DSL Transceiver Most residential customers call their DSL transceiver a "DSL modem." Theengineers at the telephone company or ISP call it an ATU-R. Regardless of whatit's called, it's the point where data from the user's computer or network isconnected to the DSL line. The transceiver can connect to a customer'sequipment in several ways, though most residential installation uses USB or 10base-T Ethernet connections. While most of the ADSL transceivers sold by ISPsand telephone companies are simply transceivers, the devices used bybusinesses may combine network routers, network switches or other networkingequipment in the same platform.

CHAPTER- 4 ADSL TECHNOLOGY4.1 ADSL TECHNOLOGYADSL depends upon advanced digital signal processing and creative algorithmsto squeeze so much information through twisted-pair telephone lines. In addition, many advances have been required in transformers, analog filters, and A/D converters. Long telephone lines may attenuate signals at one megahertz (the outer edge of the band used by ADSL) by as much as 90 dB, forcing analogsections of ADSL modems to work very hard to realize large dynamic ranges, separate channels, and maintain low noise figures. On the outside, ADSL looks simple -- transparent synchronous data pipes at various data rates over ordinary telephone lines. On the inside, where all the transistors work, there is a miracle of modern technology.

FIGURE 4.1 DIAGRAM OF ADSL COMPONENTS

ADSL depends on advanced digital signal processing and creative algorithms tosqueeze so much information through twisted-pair telephone lines. In addition,many advances have been required in transformers, analog filters, andanalog/digital (A/D) converters. Long telephone lines may attenuate signals at 1MHz (the outer edge of the band used by ADSL) by as much as 90 dB, forcinganalog sections of ADSL modems to work very hard to realize large dynamicranges, separate channels, and maintain low noise figures. On the outside,ADSL looks simple—transparent synchronous data pipes at various data ratesover ordinary telephone lines. The inside, where all the transistors work, is amiracle of modern technology. Figure 2 displays the ADSL transceivernetworkend. This Diagram Provides an Overview of the Devices That Make Up theADSL4.2 ADSL TRANSCEIVER - NETWORK

FIGURE 4.2 ADSL TRANSCEIVER-NETWORK ENDTo create multiple channels, ADSL modems divide the available bandwidth of atelephone line in one of two ways: frequency-division multiplexing (FDM) orecho cancellation.FDM assigns one band for upstream data and another band for downstreamdata. The downstream path is then divided by time-division multiplexing intoone or more high-speed channels and one or more lowspeed channels. Theupstream path is also multiplexed into corresponding low-speed channels. Echocancellation assigns the upstream band to overlap the downstream, andseparates the two by means of local echo cancellation, a technique well knownin V.32 and V.34 modems.

With either technique, ADSL splits off a 4-kHz region for basic telephoneservice at the DC end of the band. ADSL Uses FDM and Echo Cancellation toDivide the Available Bandwidth for Services.

An ADSL modem organizes the aggregate data stream created by multiplexingdownstream channels, duplex channels, and maintenance channels together intoblocks, and it attaches an error correction code to each block. The receiver thencorrects errors that occur during transmission, up to the limits implied by thecode and the block length. At the user's option, the unit also can createsuperblocks by interleaving data within subblocks; this allows the receiver tocorrect any combination of errors within a specific span of bits. This, in turn,allows for effective transmission of both data and video signals.

FIGURE 4.3 SCHEMATIC DIAGRAM OF ADSL WORKING

CHAPTER 5 METHODS TO SPLIT THE SIGNAL5.1 METHODS TO SPLIT THE SIGNALThere are two competing and incompatible standards for ADSL. The official ANSI standard for ADSL is a system called discrete multitone, or DMT. According to equipment manufacturers, most of the ADSL equipment installed today uses DMT. An earlier and more easily implemented standard was the carrierless amplitude/phase (CAP) system, which was used on many of the earlyinstallations of ADSL.CARRIERLESS AMPLITUDE/PHASE(CAP)

FIGURE -5.1 DIAGRAM OF CAPCAP operates by dividing the signals on the telephone line into three distinctbands: Voice conversations are carried in the 0 to 4 KHz (kilohertz) band, asthey are in all POTS circuits. The upstream channel (from the user back to theserver) is carried in a band between 25 and 160 KHz. The downstream channel(from the server to the user) begins at 240 KHz and goes up to a point thatvaries depending on a number of conditions (line length, line noise, number ofusers in a particular telephone company switch) but has amaximum of about 1.5MHz (megahertz). This system, with the three channels widely separated,minimizes the possibility of interference between the channels on one line, orbetween the signals on different lines.DISCRETE MULTITONE

FIGURE 5.2 DIAGRAM OF DMT

DMT divides signals into separate channels, but doesn't use two fairly broadchannels for upstream and downstream data. Instead, DMT divides the data into247 separate channels, each 4 KHz wide. One way to think about it is to imagine that the phone company divides yourcopper line into 247 different 4-KHz lines and then attaches a modem to eachone. You get the equivalent of 247 modems connected to your computer atonce! Each channel is monitored and, if the quality is too impaired, the signal isshifted to another channel. This system constantlyshifts signals betweendifferent channels, searching for the best channels for transmission andreception. In addition, some of the lower channels (those starting at about 8KHz), are used as bidirectional channels, for upstream and downstreaminformation. Monitoring and sorting out the information on the bidirectionalchannels, and keeping up with the quality of all 247 channels, makes DMTmore complex to implement than CAP, but gives it more flexibility on lines ofdiffering quality.SPLITTING THE SIGNAL: FILTERS

FIGURE-5.3 DIAGRAM OF LPFIf you have ADSL installed, you were almost certainly given smallfilters to attach to the outlets that don't provide the signal to your ADSLmodem. These filters are low-pass filters -- simple filters that block all signalsabove a certain frequency. Since all voice conversations take place below 4KHz, the low-pass (LP) filters are built to block everything above 4 KHz,preventing the data signals from interfering with standard telephone calls.

CHAPTER- 6 STANDARDS AND ASSOCIATION6.1STANDARDS AND ASSOCIATIONSThe American National Standards Institute (ANSI), working group T1E1.4,approved the first ADSL in 1995. It supported data rates up to 6.1Mbps (ANSIStandard T1.413). The European Technical Standards Institute(ETSI)contributed an Annex to T1.413 to reflect European requirements.T1.413 (IssueI) was limited to a single terminal interface at the premise end.Issue II(T1.413i2), approved in 2001, expanded the standard to include a multiplexedinterface at the premise end, protocols for configuration and networkmanagement, and other improvements.Work towards an Issue III was ultimately submitted to the internationalstandards body, the ITU-T, to develop the international standards for ADSL. TheITU-T standards for ADSL are most commonly referred to as G.lite (G.992.2)and G.dmt (G.992.1)–both of which are approved in June of 1999. Having aninternational standard has aided in moving towards vendor interoperability andservice provider acceptance, further increasing deployment, and ultimatelyavailability to the consumer.The ATM Forum has recognized ADSL as a physical layer transmissionprotocol for unshielded twisted pair media. The DSL Forum was formed inDecember of 1994 to promote the DSL concept and facilitate development ofDSL system architectures, protocols, and interfaces for major DSL applications.The DSL Forum has expanded its efforts to address marketing issuessurrounding awareness, and enabling high-speed applications via DSL. TheDSL Forum has approximately 340 members representing service providers,equipment manufacturers, and content developers from throughout the world.

CHAPTER- 7 DISTANCE LIMITATIONS7.1 DISTANCE LIMITATIONSPrecisely how much benefit you see will greatly depend on how far you arefrom the central office of the company providing the ADSL service. ADSL is adistance-sensitive technology: As the connection's length increases, the signalquality decreases and the connection speed goes down. The limit for ADSLservice is 18,000 feet (5,460 meters), though for speed and quality of servicereasons many ADSL providers place a lower limit on the distances for theservice. At the extremes of the distance limits, ADSL customers may see speedsfar below the promised maximums, while customers nearer the central officehave faster connections and may see extremely high speeds in the future. ADSLtechnology can provide maximum downstream (Internet to customer) speeds ofup to 8 megabits per second (Mbps) at a distance of about 6,000 feet (1,820meters), and upstream speeds of up to 640 kilobits per second (Kbps). Inpractice, the best speeds widely offered today are 1.5 Mbps downstream, withupstream speeds varying between 64 and 640 Kbps. You might wonder, ifdistance is a limitation for DSL, why it's not also a limitation for voicetelephone calls. The answer lies in small amplifiers called loading coils that thetelephone company uses to boost voice signals. Unfortunately, these loadingcoils are incompatible with ADSL signals, so a voice coil in the loop betweenyour telephone and the telephone company's central office will disqualify youfrom receiving.ADSL. Other factors that might disqualify you from receiving ADSL include:Bridge taps - These are extensions, between you and the central office, thatextend service to other customers. While you wouldn't notice these bridge tapsin normal phone service, they may take the total length of the circuit beyond thedistance limits of the service provider.Fiber-optic cables - ADSL signals can't pass through the conversion from analogto digital and back to analog that occurs if a portion of your telephone circuitcomes through fiber-optic cables.Distance - Even if you know where your central office is (don't be surprised ifyou don't -- the telephone companies don't advertise their locations), looking ata map is no indication of the distance a signal must travel between your houseand the office

CHAPTER-8 DSL FUTURE8.1 DSL FUTUREADSL is competing with technologies such as cable-modem access and satelliteInternet access for high-speed connections from consumers to the Internet. According to IDC, a market-analysis firm based in Framingham, MA, approximately 330,000 households in the United States were connected to the Internet via DSL in 1999, compared to 1,350,000 households with cable modems. By 2003, IDC estimates that the number of households with cable modems will have risen to 8,980,000, while DSL will have raced into the broadband lead with 9,300,000 households. Currently, ADSL is limited (by U.S.Federal Communications Commission regulations) to a maximum of 1.5 megabits per second. Current technology can provide a theoretical maximum of up to 7 megabits per second, and research promises even greater performance inthe future with protocols like G.Lite and VDSL.ADSL depends on advanced digital signal processing and creative algorithms tosqueeze so much information through twisted-pair telephone lines. In addition,many advances have been required in transformers, analog filters, andanalog/digital (A/D) converters. Long telephone lines may attenuate signals at 1MHz (the outer edge of the band used by ADSL) by as much as 90 dB, forcinganalog sections of ADSL modems to work very hard to realize large dynamicranges, separate channels, and maintain low noise figures. On the outside,ADSL looks simple—transparent synchronous data pipes at various data ratesover ordinary telephone lines. The inside, where all the transistors work, is amiracle of modern technology.

CHAPTER 9 APPLICATIONS9.1APPLICATIONSDigital Subscriber Line (DSL) technology is a solution to the everincreasing demand for more bandwidth by business and residential consumers. Below are some current applications of DSL:High-speed Internet accessCorporate Local Area Network (LAN) accessE-CommerceTelecommuting / Virtual Private Network (VPN)Distance learningVideo-On-DemandVoice over Internet Protocol (VoIP) / IP dial toneVideo conferencingMedical imagingReal-time information exchangeEntertainment - online gamingDSL will let you use the Internet as it was meant to be. Web pages will loadonto your computer instantly, files will download with amazing speed and you'llbe able to play network games with relative ease. Soon streaming audio andvideo will be a common place application for DSL.

FIGURE 9.1 DSL COMPARISION

FIGURE 9.2 TECHNOLOGY WISE MARKET SHARE OF BROADBAND SHARES

FIGURE 9.3 DSL TECHNOLOGY IN VARIOUS COUNTRIES

*ALL FIGURES END TILL 2009

FIGURE 9.4 PIE CHART OF WIRELESS MARKET

CHAPTER-10 CONCLUSION10.1CONCLUSIONASDL technology is asymmetric, allowing more bandwidth for downstreamthan upstream data flow. This asymmetric technology combined with always-onaccess makes ASDL ideal for users who typically download much more datathan they send. An ASDL modem is connected to both ends of a twisted-pair telephone line to create three information channels: a high-speed downstream channel, amedium-speed duplex channel, and a basic telephone service channel. ADSLmodems create multiple channels by dividing the available bandwidth of atelephone line using either frequency-division multiplexing (FDM) or echocancellation. Both techniques split off a 4-kHz region for basic telephone service at the DC end of the band .

REFERENCES:www.howstuff.comwww.dsl.netwww.athenet.netMagazine referred : Electronics For You