BANSAL INSTITUTE OF ENGINEERING & TECHNOLOGY, LUCKNOW

Seminar REPORT

ON

DIGITAL SUBSCRIBER LINE

SUBMITTED TO: SUBMITTED BY:

MR.PAWAN KUMAR SAINI ANANT PRATAP SINGH

H.O.D. (EC) EC- 3rd yr.

ROLL NO. 1042231009

DSL TECHNOLOGY

ACKNOWLEDGEMENT

It is pleasure for me to present this seminar regarding the“DIGITAL SUBSCRIBER LINE (DSL)” Today, high-speed Internet access has become quite a necessity, not only in the advanced nations but also in many of the third world countries.

I would like to thank everyone who helped to see this seminar to completion. In particular, I would like to thank my seminar incharge Mr. Ankur Shukla for their moral support and guidance to comlete my seminar on time.

I am sincerely thankful to Mr. Pawan Kr. Saini(HOD EC.) for giving me suggestion to complete my seminar in a right way and at the time.

I express my gratitude to all my friends and classmates for their support and help in the seminar.

ANANT PRATAP SINGH

E.C 3RD YR.

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DSL TECHNOLOGY

S.NO. NAME OF TOPICS PAGENO.1. HISTORY OF DSL 42. WHAT IS DSL? 53. BASIC TECHNOLOGY(OPERATION) 64. COMPARATIVE STUDY OF DSL FLAVORS 75. WHAT IS CABLE INTERNET CONNECTION? 76. TYPES OF DSL 8-97. ADSL(Asymmetric Digtal Subscriber line) 88. VDSL(Very high-bit rate Digital Subscriber line) 89. RADSL(Rate-Adaptive Digital Subscriber line) 8

10. HDSL(High bit/data rate Digital subscriber line) 811. ISDN DSL(Integrated Service Digital Network) 812. DSL DEVICE 813. DSL VS CABLE 10-1114. APPLICATION 1115. ADVANTAGES 1216. DISADVANTAGE 1317. SUMMARY OF DSL 1418. CONCLUSION 1519. REFERENCE 16

LISTS OF FIGURES

S.NO FIGURE NAME PAGE NO.

1. BASIC DSL NETWORK 52. BASIC TECHNOLOGY(OPERATION) 63. COMPARATIVE STUDY OF DSL FLAVORS 74. BASIC CABLE NETWORK 75. WORKING OF A SIMPLIFIED ADSL 86. GENERAL MODEM FOR DSL DEVICE 10

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DSL TECHNOLOGY

HISTORY OF DSL

MODEM (Modulator-Demodulator) used for communication between any two computers

through a PSTN line uses Modulation and Demodulation techniques for Digital-Analog and

Analog-Digital conversion, respectively.

In 1969, AT&T revised the tariffs to allow customer-provided devices (modems) to beConnected

to PSTN lines for transferring data, with the following conditions:

Restriction in output power and energy levels

Connection to the PSTN (Public Switched Telephone Network) thru the telephone company-

provided protective devices (Data Access Arrangement).

All the network-control signaling ( Dialling , Busy signals, etc.) performed with the

Telephone company -provided equipment at the connection point.Under these conditions,

modem technology had to come up with the following new Techniques in order to achieve

higher data rates (from 19.2 Kbps thru 56 Kbps):

Error Correction

Echo Cancellation

Modem data rates are calculated using Claude Shannon’s formula:

C = B * log2 (1+ S/N) where ,C = Channel Capacity (2400 to 2800 Hz)

B = Bandwidth (24000 bps)

S/N = Signal-to-Noise Ratio (24 to 30 dBs)

The limitations in achieving higher data rates thru these voice band lines are mainly due to the

core network and not the bandwidth availability of the copper wire of the telephone network.

Filters at the core of the network limit the voice-grade bandwidth to approximately 3.3 KHz. In

the absence of these filters, the copper wires can up to a few frequenciesMHz.It is precisely this

aspect that is made use of in the DSL technology, which came into existence in the late 1980s.

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DSL TECHNOLOGY

WHAT IS DSL?

Digital Subscriber Line (DSL) is a technology that provides digital data transmission over the

existing wires of local telephone network. DSL service is delivered simultaneously with regular

telephone on the same telephone line. This is possible because DSL uses a higher frequency.

These frequency bands are subsequently separated by filtering.

Fig1: Basic DSL network

Digital Subscriber Line (DSL) is a broadband high-speed Internet technology that brings high-

bandwidth information to home and offices over ordinary copper telephone lines.

It assumes that digital data does not require changing into analog form and back to digital form.

Digital data is transmitted directly to the computer, as is, exploiting the maximum

bandwidth and the wide range of unused frequencies available in the existing copper wire of

telephone networks for high-speed broadband communication. Moreover, the signal can also be

separated, if one chooses, so that some of the bandwidth is used to transmit an analog signal for

simultaneously using the telephone line for voice.

Following are some of the key features of DSL:Distance- sensitive technology.

Internet connection is always ON.

Simultaneous use of the phone line for voice as well as data traffic.

Internet Connection is highly reliable and secure.

High Speed (Mbps) vis-à-vis a regular modem (56 Kbps max).

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DSL TECHNOLOGY

Basic technology(Operation)

Telephones are connected to the telephone exchange via a local loop, which is a physical pair of

wires. Prior to the digital age, the use of the local loop for anything other than the transmission of

speech, encompassing an audio frequency range of 300 to 3400 Hertz (voiceband or commercial

bandwidth) was not considered. However, as long distance trunks were gradually converted from

analog to digital operation, the idea of being able to pass data through the local loop (by utilizing

frequencies above the voice band) took hold, ultimately leading to DSL. The local loop

connecting the telephone exchange to most subscribers has the capability of carrying frequencies

well beyond the 3.4 kHz upper limit of POTS.

Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL

takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels

starting between 10 and 100 kHz, depending on how the system is configured. Allocation of

channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new

channels are deemed unusable.

Because DSL operates above the 3.4 kHz voice limit, it cannot pass through a load coil . Load

coils are, in essence, filters that block out any non-voice frequency. They are commonly set at

regular intervals in lines placed only for POTS service. A DSL signal cannot pass through a

properly installed and working load coil, while voice service cannot be maintained past a certain

distance without such coils. Therefore, some areas that are within range for DSL service are

disqualified from eligibility because of load coil placement.

Fig2: Basic Technology(Operation)

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DSL TECHNOLOGY

Comparative Study of DSL Flavors

XDSL Series Type Down Speed Up Speed DistanceADSL Asymmetric 6-8Mbps 640Kbps 12000-18000ft.ADSL2 Asymmetric 12 Mbps 1Mbps 6000ft.ADSL2+ Asymmetric 27 Mbps 1Mbps 3000ft.RADSL Asymmetric 640-2200Kbps 27-1088Kbps 18000ft.VDSL Asymmetric/Symmetric 13-52 Mbps 1.5-2.3Mbps 4500ft.HDSL Symmetric 2.3 Mbps 2.3Mbps 12000ft.IDSL Symmetric 144 Kbps 144Kbps Morethan 2000ft.

Fig3: Comparative study of different DSL flavors

What Is a Cable Internet Connection?

Cable internet connection is an internet connection designed to operate over existing cable TV

lines. Cable Internet access requires a Cable Modem (CM) at the customer's premises and a

Cable Modem Termination System (CMTS) at a cable operator facility. The two are connected

via coaxial cable because the coaxial cable used by cable TV provides much greater bandwidth

than telephone lines. Cable Internet systems can typically operate where the distance between the

modem and the termination system is up to 100 miles (160 km).

Fig4:Basic Cable network

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DSL TECHNOLOGY

TYPES OF DSL

ADSL(Asymmetric Digital Subscriber Line)

VDSL(Very high-bit-rate Digital Subscriber Line)

SDSL(Symmetric Digital Subscriber Line )

RADSL(Rate Adaptive Digital Subscriber Line)

HDSL(High bit/data rate Digital Subscriber Line)

ISDN DSL(Integrated Service Digital Network)

Asymmetric Digital Subscriber Line (ADSL):

Most home and small business users typically use ADSL.

The transfer of data from the internet to PC is much faster than the transfer from PC

to internet.

Downstream speeds for ADSL range from 1.59 Mbps, while upstream speeds are up

to 1.5 Mbps, for a distance of 18,000 feet from the service providers premises.

Fig5: Working of a simplified ADSL

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DSL TECHNOLOGY

Very high-bit-rate Digital Subscriber Line(VDSL):

Provides high speed internet connection but works only over a short distance.

Symmetric Digital Subscriber Line (SDSL):

Does not allows to use the phone at the same time. But internet speed of sending and

receiving data is same.

Rate Adaptive Digital Subscriber Line (RADSL):

This service is a variation of ADSL but the modem can adjust the internet speed .

High bit/data rate Digital Subscriber Line(HDSL):

HDSL was the first DSL technology that used a higher frequency spectrum of copper,

twisted pair cables.

Integrated service digital network(ISDN DSL):

Symmetric data rates of up to 144 kbps using existing phone lines.

Capable of using the same modem or terminal adaptor used for ISDN and is always

available.

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DSL TECHNOLOGY

DSL DEVICES

DSL is actually not a physical line, but a modem pair. One DSL modem is located at the

customer premises (Customer Premise Equipment or CPE) and another DSL Access Multiplexer

(DSLAM) is at the Central Office (CO). These two modems create a Digital Subscriber Line or

DSL. DSL modems transmit data at the rate of up to 160 Kbps over copper lines, up to 18000

feet.DSL Modem or DSL Transceiver, as it is also referred to as, is connected to the customer’s

computer via USB or a 10-Base T connection.

DSLAM at the Central Office or the Access Provider is the one that actually makes the DSL

happen . It accepts connections from various customers and aggregates them into a single high

capacity connection to the Internet. In addition, the DSLAM also does IP routing and Dynamic

IP address assignment.

Fig6: GENERAL MODEM FOR DSL DEVICE

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DSL TECHNOLOGY

DSL V/S CABLE

Both DSL and Cable Modem technologies offer high-speed Internet access. Even though they

are similar in many respects, the two technologies differ on some fundamental aspects such as

speed, availability , bandwidth, security, reliability and quality of service.

Availability:

DSL was first designed in the 1970‘s whereas Cable‘s HFC was designed in the 80s and 90s.

Roughly 80 to 85 percent of America's 68 million cable TV subscribers (say, 55 million or so)

can get high-speed access, says Instat-MDR analyst Mike Paxton. DSL access is a little spottier,

though Instat’s Ernie Bergstrom puts the number above 50 million. In terms of worldwide

broadband market share, currently DSL has higher market share compared to Cable but in

coming years picture may change.

Speeds:The topic of "which is better and faster" has been a highly debated topic, and still there doesn't

appear to be a clear winner. DSL offers users a choice of speeds ranging from 144 Kbps to

1.5Mbps. Cable modem download speeds are typically up to 2 times faster than 1.5Mbps DSL,

but the reason there is no clear speed winner is because cable technology is based on shared

bandwidth, with many factors influencing a user‘s download speed. With shared bandwidth the

speed fluctuates depending on the number of subscribers on the network. With DSL, the

connection is kind of dedicated and not shared, and user gets more or less an invariable speed.

This is one reason why cable broadband providers don't often publish speed information.

In more rural areas with fewer subscribers, users bound to have faster download speeds than a

user in a metropolitan center. Because cable modem speeds fluctuate, it is difficult to gauge an

exact download speed. On the upload stream, however, cable and DSL are closely matched for

speed. Both DSL and cable Internet speeds are largely dependent on the service provider and

either the distance away from the switching station a user is or how many users are in an

immediate area.

Bandwidth:

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DSL TECHNOLOGY Cable modem technology delivers “shared” bandwidth within the neighbourhood, while DSL

delivers“dedicated” bandwidth. DSL typically is provided in the range from 128 kbps to 1.544

Mbps, varying as the equipment.

Security: DSL can be considered to be more secure of the two, more due to a perceived weakness in the cable modem. All cable modem customers in a region belong to the same LAN, thus opening avenues for file sharing and other menaces of a typical network neighbourhood. This calls for security firewalls, strict authentication and packet filtering mechanisms to be built into cable modem standard specifications.

Reliability: Both DSL and Cable provide an “always on connection” capability, thereby giving a “Static IP

address” to the session; and in turn, providing a fixed target to network attackers. As a result,

many DSL and cable customers have to purchase a DSL Router or a Cable Router, that enhances

the functionality of a basic modem with security features such as packet filtering and network

address translation. Customers can choose from a variety of precautions offered by the

broadband router, to suit their applications.

Despite tall claims by vendors about out-weighing the benefits of one another, both DSL and

Cable modem providers are working towards winning customers and expanding their customer

base. Drastically cutting costs, providing more value-added services, improvising on the security

features and constantly withstanding competitive pressures from vendors of the other forms of

technology, both forms of broadband technology are here to stay for some more time.

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DSL TECHNOLOGY

APPLICATIONS

Interactive Video – movies on demand , video on demand , video conferencing.

High-speed Data communication – Internet access , Telecommuting , Remote LAN

access ,specialized network access.

ADVANTAGES

DSL service is always ON and we can still use the phone for voice calls.

Broadband speed is much faster than dial up service.

Fixed monthly billing, regardless of time usage.

Digital data is directly transmitted to computer as digital data which uses much wider

bandwidth for transmitting.

DISADVANTAGES

DSL has one significant downside:

As you move away from the central office , the connection becomes slower.

This results is distortion of signal.

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DSL TECHNOLOGY

Summary Of DSL

The growth in demand for access to the Internet by business and residential end users has been

increasing for a number of years. The content available on the Internet and the applications

required to access it have also developed to meet end user demand and become ever more

complex and sophisticated and have, in turn, driven demand for greater delivered bandwidths to

maximize operational performance.

Forecasts for growth in bandwidth requirements are based upon a number of factors, future

demand for services such as “Triple Play” using standard and high definition IP Television is

often cited as a driver for the provision of ever increasing bandwidths although there is

considerable debate over the dynamics of this market. This paper assumes that the demand for

higher bandwidths will continue to increase, and examines the capabilities and limitations and

the current and future roles that Digital Subscriber Loop (DSL) technologies have in delivering

ever higher bandwidths to end users to meet demand for access to developing services.

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DSL TECHNOLOGY

Conclusion

The development of Digital Subscriber Loop technologies has enabled the delivery of high

bandwidth broadband services to end users connected to the copper access network.

However, the intrinsic limitations of the copper cables impose a finite limit on the maximum

bandwidth that can be delivered to end users. Given that forecasts for bandwidth demand

indicate a continuous increase, DSL technologies seem to offer - at best - an interim solution to

the problem of providing genuinely fast broadband services.

Although end user demand for standard and high density IP Television is often hailed as

a major driver for the provision of high-bandwidth networks, the continuing slow take-up of

IPTV offerings in the UK would seem to make it unlikely that this sector will be sufficient to

drive a significant increase in bandwidth in the UK. Instead, it is the ever-greater requirements

for bandwidth to access more sophisticated content and to efficiently run the applications needed

to exploit them which is likely to make the ubiquitous provision of high-bandwidth services a

necessity, for both business and domestic users across a range of urban, rural and suburban

environments.

As requirements for universal Internet access combined with greater bandwidth increase, and the

associated problems with providing high bandwidths over legacy copper access networks

threaten to expand the phenomenon of the digital divide to include not just remote rural areas but

populous suburbs as well, so increased attention will need to be devoted to the underlying issues

of broadband access.

As already discussed, one obvious solution lies in the construction of Next Generation Access

networks using both hybrid copper/fibre networks and all-fibre networks to deliver bandwidths

of 50 Mbps and above to large numbers of end users. Negative aspects, however, include the

substantial levels of investment by network operators or public/private partnerships required to

make this a reality, and the degree of disruption inherent in laying new infrastructure by

trenching in existing built environments. Solutions to the latter exist in the possibility of running

fibre circuits through sewers, or in carrying them on overhead rights-of-way, but both suffer

from drawbacks in terms of the vulnerability to damage of the circuits and the potential difficulty

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DSL TECHNOLOGY

REFERENCES

International Telecommunication Union (ITU). G.992.1 (G.dmt), G.992.2 (G.lite)standards information. http://www.itu.int

American National Standards Institute (ANSI). ANSI TI.413-1998, ADSL MetallicInterface. http://www.ansi.org

Universal ADSL Working Group. G.lite standards information. http://uawg.org

Standards Committee T1-Telecommunications. XDSL standards and relevantdocuments from T1E1.4 Working group. http://www.t1.org

European Telecommunications Standards Institute (ETSI). ADSL, VDSL and SDSLstandards. http://www.etsi.org

Internet Engineering Task Force (IETF). ADSL MIB working group.http://www.ietf.org, http://www.ietf.org/html-charters/adslmib-charter.html

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