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A Mini project training on

BROADBAND ADSL/VDSL TECHNOLOGY IN BSNL

Submitted in partial fulfillment of the requirements for the award of theDegree of

BACHELOR OF TECHNOLOGY

in

ELECTRONICS AND COMMUNICATION ENGINEERING

by

M.RAMYA 09P31A0469

UNDER THE ESTEEMED GUIDANCE OF

Mr. N.RAJESH BABUM.Tech , Associate Professor,ECE

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

SRI SAI ADITYA INSTITUTE OF SCIENCE AND TECHNOLOGY

(Affiliated to JNTUK, Kakinada& Approved by AICTE, New Delhi)

Surampalem, East Godavari District

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Department of

Electronics and Communication Engineering

CERTIFICATE

This is to certify that the mini project report entitled

BROADBAND IMPLEMENTATION OF MPLS TECHNOLOGY IN BSNL

being submitted by

M.RAMYA 09P31A0469

This is to certify that the mini project work titledBROADBAND ADSL/VDSL

TECHNOLOGYIN BSNL is a bonafide work ofM.RAMYA carried out in partialfulfillment of the requirements under our guidance.

Project guide Head of the Department

Mr. N.RAJESH BABU, M.Tech Mr. R.V.V.KRISHNA,

Associate Professor , ECE M.Tech(Ph.D.)

HOD, ECE

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ACKNOWLEDGEMENT

Performing Mini Project is an important role in shaping up an

Engineering student for practical knowledge and to be update with latest

Technologies. First of all, I would like to express my attitude towards Head of

the Department of Electronics and Communication Engineering

Mr.R.V.V.KRISHNA, M.Tech(Ph.D.), Associate Professor and HOD,ECE for his

guidance throughout our Mini Project work. With great pleasure we want to

take this opportunity to express our heartfelt gratitude to all the people who

helped in making this Mini Project work a grand success.

We would like to thank Mr.N.RAJESH BABU , M.Tech ,Associate Professor,

ECE as my mini project guide for giving valuable suggestions.

First of all we are highly indebted to Principal Dr. CH.SRINIVASA

RAO, M.Tech, Ph.D., FIETEfor giving us the permission to carry out this Mini

Project.We would like to thank the HOD & Other Teaching Staff of ECE

Department for sharing their knowledge with us.

We thank Sri K.SURESH KUMAR S.D.E and Co-Staff Members, BSNL,

Rajahmundry for extending their utmost support and cooperation in providing

successful completion of the Project.

We thank Sri V.RAMESH BABU, Assistant General Manager(admn.) of

BSNL, Rajahmundry for extending their utmost support and cooperation in

providing all the provisions for the successful completion of the Project.

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ABSTRACT

Digital Subscriber Line (DSL) technology is a modem technology

that uses existing twisted-pair telephone lines to transport high-bandwidth

data, such as multimedia and video, to service subscribers. The term

Xdsl covers a number of similar yet competing forms of DSL , including

ADSL , SDSL , HDSL , RADSL , and VDSL . xDSL is drawing significant

attention from implementers and service providers because it promises to

deliver high-bandwidth data rates to dispersed locations with relatively

small changes to the existing telco infrastructure .

xDSL services are dedicated , point-to-point , public network access over

twisted-pair copper wire on the local loop (last mile) between a

network service provider (NSPs) central office and the customer site , or

on local loops created either intra-building or intra campus. Digital The

benefits Subscriber Line (DSL) technologies has revolutionized Internet

access of DSL technology, coupled with the deregulation of the tele-

communications industry, have caused in increase in the number ofservice providers (xSP) offering DSL services.

Everyone from ILECs to CLECs to ISPs are offering DSL services to

homes and Businesses-with Asymmetric Digital Subscriber Line (ADSL)

currently being the most common and cost effective choice. Research

into DSL technologies has produced variants of ADSL to help resolve

issues users are faced with today, as well as plan for future

implementations. One of these variants is Very High Bit-Rate Digital

Subscriber Line (VDSL). VDSL differs from the other DSL technologies

primarily in the areas of speed and distance. Lower costs, competition

with other technologies and forward thinking for future bandwidth

requirements are contributing to making VDSL a variable technology for

even wider implementation. Currently the primary focus in xDSL is the

. development and deployment of ADSL and VDSL technologies and

architectures.

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INDEX

TABLE OF CONTENTS PAGE NO:

1. Asymmetric Digital Subscriber Line (ADSL) 6-11

1.1ADSL capabilities

1.2ADSL technology

1.3ADSL standards and associations

1.4ADSL market status

2. Very High Data Rate Digital Subscriber Line (VDSL) 12-14

2.1VDSL projected capabilities

3. ADSL 15-22

3.1Overview

3.2Operation

3.3Interleaving and fast path

3.4Installation problems

3.5Transport protocols

3.6ADSL standards

4. Digital Subscriber Line Access Multiplexer 23-26

4.1Path taken by data to DSLAM

4.2 Role of DSLAM

5. Conclusion 27

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CHAPTER-1

Asymmetric Digital Subscriber Line (ADSL)

ADSL technology is asymmetric. It allows more bandwidth

downstream from an NSPs Central office to the customer sitethan

upstream from the subscriber to the central office. This asymmetry,

combined with always-on access (which eliminates call setup), makes

ADSL ideal for Internet/intranet surfing, video-on-demand, and remote

LAN access. Users of these applications typically download much more

information than they send. ADSL transmits more than 6 Mbps to a

subscriber, and as much as 640 kbps more in both directions (shown in

Figure ). Such rates expand existing access capacity by a factor of 50

or more without new cabling. ADSL can literally transform the existing

public information network from one limited to voice, text, and low-

resolution graphics to a powerful, ubiquitous system capable of bringing

multimedia, including full motion video, to every home this century.

FIGURE 1

1.1 ADSL Capabilities

An ADSL circuit connects an ADSL modem on each end of a twisted-

pair line, creating three information channels - a high speed downstream

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channel, a medium speed duplex channel, and a basic telephone service

channel. The basic telephone service channel is split off from the

digital modem by filters, thus guaranteeing uninterrupted basic telephone

service, even if ADSL fails. The high-speed channel ranges from 1.5 to

6.1 Mbps, and duplex rates range from 16 to 640 kbps. Each channel can

be submultiplexed to form multiple lower-rate channels.

ADSL modems provide data rates consistent with North American T1

1.544 Mbps and European E1 2.048 Mbps digital hierarchies (see Figure

1.2) and can be purchased with various speed ranges and capabilities.

The minimum configuration provides 1.5 or 2.0 Mbps downstream and a

16 kbps duplex channel; others provide rates of 6.1 Mbps and 64 kbps

duplex. Products with downstream rates upto 8 Mbps and duplex rates

up to 640 Kbps are available today ADSL modems accommodate

Asynchronous Transfer Mode (ATM) transport with variable rates and

compensation for ATM overhead, as well as IP protocols. Downstream

data rates depend on a number of factors, including the length of the

copper line, its wire gauge, presence of bridged taps, and cross-coupled

interference. Line attenuation increases with line length and frequency

and decreases as wire diameter increases. Ignoring bridged taps ADSL

performs as shown in Table 1.1.

Table 1: Claimed ADSL Physical-Media Performance

Data

Rate

Wire

gauge

Wire

size

Distance

1.5 or

2Mbps

24

AWG

0.5mm 5.5km

1.5 or

2Mbps

26

AWG

0.4mm 4.6km

6.1Mbps 24

AWG

0.5mm 3.7km

1.5 or 2

Mbps

26

AWG

0.4mm 2.7

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Table 2: This chart shows the speeds for downstream bearer and duplex

bearer channels

Although the measure varies from telco to telco , these capabilities can

cover up to 95% of a loop plant, depending on the desired data rate.

Customers beyond these distances can be reached with fiber-based

digital loop carrier (DLC) systems . As these DLC systems become

commercially available , telephone companies can offer virtually

ubiquitous access in a relatively short time.

Many applications envisioned for ADSL involve digital compressedvideo . As a real-time signal, digital video cannot use link- or network-

level error control procedures commonly found in data communications

systems . ADSL modems therefore incorporate forward error correction

that dramatically reduces errors caused by impulse noise . Error

correction on a symbol-by-symbol basis also reduces errors caused by

continuous noise coupled into a line.

Downstream Bearer Channels

n*1.536 Mbps 1.536 Mbps

3.072 Mbps

4.608 Mbps

6.144 Mbps

N*2.048 Mbps 2.048 Mbps

4.096 Mbps

Duplex Bearer Channels

C Channel 16 kbps

64 kbps

Optional Channel 160 kbps

384 kbps

544 kbps

576 kbps

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1.2 ADSL Technology

ADSL depends on advanced digital signal processing and creative

algorithms to squeeze so much information through twisted-pair telephone

lines. In addition, many advances have been required in transformers, analog

filters, and analog/digital (A/D) converters. Long telephone lines may

attenuate signals at 1 MHz (the outer edge of the band used by ADSL) by as

much as 90 dB, forcing analog sections 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. The inside, where all

the transistors work, is a miracle of modern technology.

To create multiple channels, ADSL modems divide the available bandwidth of

a telephone line in one of two ways-frequency division multiplexing (FDM)

or echo cancellation-as shown in figure 1.3. FDM assigns one band for

upstream data and another band for downstream data .The downstream path is

then divided by time-division multiplexing into one or more high-speed

channels and one or more low-speed channels .The upstream path is alsomultiplexed into corresponding low-speed channels .Echo cancellation assigns

the upstream band to overlap the downstream, and separates the two by means

of local echo cancellation, a technique well known in V.32 and V.34 modems.

With either technique, ADSL splits off a 4khz region for basic telephone

service at the DC end of the band.

Figure 2: Graph of Upstream and Downstream

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An ADSL modem organizes the aggregate data stream created by multiplexing

downstream channels, duplex channels, and maintenance channels together into

blocks, and attaches an error correction code to each block. The receiver then

corrects errors that occur during transmission up to the limits implied by the

code and the block length. The unit may, at the users option, also create

superblocks by interleaving data within subblocks; this allows the receiver to

correct any combination of errors within a specific span of bits. This in turn

allows for effective transmission of both data and video signals.

1.3 ADSL Standards and Associations

The American National Standards Institute (ANSI) Working Group

T1E1.4 recently approved an ADSL standard at rates up to 6.1 Mbps (ANSI

Standard T1.413). The European Technical Standards Institute (ETSI)

contributed an annex to T1.413 to reflect European requirements. T1.413

currently embodies a single terminal interface at the premises end. Issue II,

now under study by T1E1.4, will expand the standard to include a multiplexed

interface at the premises end, protocols for configuration and network

management, and other improvements.

The ATM Forum and the Digital Audio-Visual Council (DAVIC) have both

recognized ADSL as a physical-layer transmission protocol for UTP media.

The ADSL Forum was formed in December 1994 to promote the ADSL

concept and facilitate development of ADSL system architectures, protocols,

and interfaces for major ADSL applications. The forum has more than 200

members, representing service providers, equipment manufacturers, and

semiconductor companies throughout the world. At present, the Forums

formal technical work is divided into the following six areas, each of which is

dealt with in a separate working group within the technical committee:

ATM over ADSL (including transport and end-to-end architecture aspects)

Packet over ADSL (this working group recently completed its work)

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CPE/CO (customer premises equipment/central office) configurations and

interfaces

Operations

Network management

Testing and interoperability

1.4 ADSL Market Status

ADSL modems have been tested successfully in more than 30 telephone

companies, and thousands of lines have been installed in various technology

trials in North America and Europe. Severaltelephone companies plan market

trials using ADSL, principally for data access, but also including video

applications for uses such as personal shopping, interactive games, and

educationalprogramming.

Semiconductor companies have introduced transceiver chipsets that are

already being used in market trials. These chipsets combine off-the-shelfcomponents, programmable digital signal processors, and custom ASICs

(application-specific integrated circuits). Continued investment by these

semiconductor companies has increased functionality and reduced chip count,

power consumption, and cost, enabling mass deployment of ADSL-based

services.

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CHAPTER-2

Very-High-Data-Rate DigitalSubscriber Line (VDSL)

It is becoming increasingly clear that telephone companies around theworld are making decisions to include existing twisted-pair loops in their

next-generation broadband access networks. Hybrid fiber coax (HFC), a

shared-access medium well suited to analog and digital broadcast, comes up

somewhat short when used to carry voice telephony, interactive video, and

high-speed data communications at the same time. Fiber all the way to the

home (FTTH) is still prohibitively expensive in a marketplace soon to be

driven by competition rather than cost. An attractive alternative, soon to be

commercially practical, is a combination of fiber cables feeding neighborhood

optical network units (ONUs) and last-leg-premises connections by existing or

new copper. This topology, which is often called fiber to the neighborhood

(FTTN), encompasses fiber to the curb (FTTC) with short drops and fiber to

the basement (FTTB), serving tall buildings with vertical drops.

One of the enabling technologies for FTTN is VDSL. In simple terms, VDSL

transmits high speed data over short reaches of twisted-pair copper telephone

lines, with a range of speeds depending on actual line length. The maximum

downstream rate under consideration is between 51 and 55 Mbps over lines up

to 1000 feet (300 m) in length. Downstream speeds as low as 13 Mbps over

lengths beyond 4000 feet (1500 m) are also common. Upstream rates in early

models will be asymmetric, just like ADSL, at speeds from 1.6 to 2.3 Mbps.

Both data channels will be separated in frequency from bands used for basic

telephone service and Integrated Services Digital Network (ISDN), enabling

service providers to overlay VDSL on existing services. At present the two

high-speed channels are also separated in frequency. As needs arise for higher-

speed upstream channels or symmetric rates, VDSL systems may need to use

echo cancellation.

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2.1 VDSL Projected Capabilities

Although VDSL has not achieved ADSLs degree of definition, it has

advanced far enough that we can discuss realizable goals, beginning with data

rate and range. Downstream rates derive from submultiples of the SONET

(Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy)

canonical speed of 155.52 Mbps, namely 51.84 Mbps, 25.92 Mbps, and 12.96

Mbps. Each rate has a corresponding target range:

Table 3:Target Ranges

Target

range(Mbps)

Distance

(feet)

Distance(meter

s)

12.96-13.8 4500 1500

25.92-27.6 3000 1000

51.84-55.2 1000 300

Upstream rates under discussion fall into three general ranges:

1.62.3 Mbps.

19.2 Mbps

Equal to downstream

Early versions of VDSL will almost certainly incorporate the slower

asymmetric rate. Higher upstream and symmetric configurations may only be

possible for very short lines. Like ADSL, VDSL must transmit compressedvideo, a real-time signal unsuited to error retransmission schemes used in data

communications. To achieve error rates compatible with those of compressed

video, VDSL will have to incorporate forward error correction (FEC) with

sufficient interleaving to correct all errors created by impulsive noise events

of some specified duration.

Interleaving introduces delay, on the order of 40 times the maximum length

correctable impulse. Data in the downstream direction will be broadcast to

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every CPE on the premises or be transmitted to a logically separated hub that

distributes data to addressed CPE based on cell or time-division multiplexing

(TDM) within the data stream itself. Upstream multiplexing is more difficult.

Systems using a passive network termination (NT) must insert data onto a

shared medium, either by a form of TDM access (TDMA) or a form of

frequency-division multiplexing (FDM). TDMA may use a species of token

control called cell grants passed in the downstream direction from the ONU

modem, or contention, or both (contention for unrecognized devices, cell

grants for recognized devices). FDM gives each CPE its own channel,

obviating a Media Access Control (MAC) protocol, but either limiting data

rates available to any one CPE or requiring dynamic allocation of bandwidthand inverse multiplexing at each CPE. Systems using active NTs transfer the

upstream collection problem to a logically separated hub that would use

(typically) Ethernet or ATM protocols for upstream multiplexing.

Migration and inventory considerations dictate VDSL units that can operate at

various (preferably all) speeds with automatic recognition of a newly

connected device to a line or a change in speed. Passive network interfaces

need to have hot insertion, where a new VDSL premises unit can be put on the

line without interfering with the operation of other modems.

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CHAPTER-3

ADSL

3.1 Overview

Figure 3: MODEM

A gateway is commonly used to make an ADSL connection.

ADSL differs from the less common symmetric digital subscriber line

(SDSL) in that bandwidth (and bit rate) is greater toward the customer

premises (known as downstream) than the reverse (known as upstream).This

is why it is called asymmetric. Providers usually market ADSL as a service

for consumers to provide Internet access in a relatively passive mode: able to

use the higher speed direction for the download from the Internet but not

needing to run servers that would require high speed in the other direction.

There are both technical and marketing reasons why ADSL is in many places

the most common type offered to home users. On the technical side, there is

likely to be more crosstalk from other circuits at the DSLAM end (where the

wires from many local loops are close to each other) than at the customer

premises. Thus the upload signal is weakest at the noisiest part of the local

loop, while the download signal is strongest at the noisiest part of the local

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loop. It therefore makes technical sense to have the DSLAM transmit at a

higher bit rate than does the modem on the customer end. Since the typical

home user in fact does prefer a higher download speed, the telephone

companies chose to make a virtue out of necessity, hence ADSL. On the

marketing side, limiting upload speeds limits the attractiveness of this service

to business customers, often causing them to purchase higher cost leased line

services instead. In this fashion, it segments the digital communications

market between business and home users.

3.2 Operation

Currently, most ADSL communication is full-duplex. Full-duplex ADSL

communication is usually achieved on a wire pair by either frequency-

division duplex (FDD), echo-cancelling duplex (ECD), or time-division

duplex (TDD). FDD uses two separate frequency bands, referred to as the

upstream and downstream bands. The upstream band is used for

communication from the end user to the telephone central office. The

downstream band is used for communicating from the central office to the

end user.Figure 4:Graph of frequency ranges of Upstream and Downstream

Frequency plan for ADSL. Red area is the frequency range used by normal

voice telephony (PSTN), the green (upstream) and blue (downstream) areas

are used for ADSL.

With standard ADSL (annex A), the band from 26.000kHz t

137.825kHz is used for upstream communication, whilecommunication.

PPSS

DDoowwnnssttrreeaa

UUppssttrreeaa

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Under the usual DMT scheme, each of these is further divided into smaller

frequency channels of 4.3125kHz. These frequency channels are

sometimes termed ''bins''. During initial training to optimize transmission

quality and speed, the ADSL modem tests each of the bins to determine the

signal-to-noise ratio at each bin's frequency. Distance from the telephone

exchange, cable characteristics, interference from AM radio stations, and local

interference and electrical noise at the modem's location can adversely affect

the signal-to-noise ratio at particular frequencies. Bins for frequencies

exhibiting a reduced signal-to-noise ratio will be used at a lower throughput

rate or not at all; this reduces the maximum link capacity but allows the

modem to maintain an adequate connection. The DSL modem will make a

plan on how to exploit each of the bins, sometimes termed "bits per bin"

allocation. Those bins that have a good signal-to-noise ratio (SNR) will be

chosen to transmit signals chosen from a greater number of possible encoded

values (this range of possibilities equating to more bits of data sent) in each

main clock cycle. The number of possibilities must not be so large that the

receiver might incorrectlydecode which one was intended in the presence of

noise. Noisy bins may only be required to carry as few as two bits, achoice

from onlyone of four possible patterns, or only one bit per bin in the case of

ADSL2+, and very noisy bins are not used at all. If the pattern of noise versus

frequencies heard in the bins changes, the DSL modem can alter the bits-per-

bin allocations, in a process called "bitswap", where bins that have become

more noisy areonly required to carry fewer bits and other channels will be

chosen to be given a higher burden. The data transfer capacity the DSL

modem therefore reports is determined by the total of the bits-per- bin

allocations of all the bins combined. Higher signal-to-noise ratios and more

bins being in use gives a higher total link capacity, while lower signal-to

noise ratios or fewer bins being used gives a low link capacity.

The total maximum capacity derived from summing the bits-per-bins is

reported by DSL modems and is sometimes termed ''sync rate''. This will

always be rather misleading, as the true maximum link capacity for user data

transfer rate will be significantly lower; because extra data are transmitted

that are termed ''protocol overhead'', reduced figures for PPPoA connections of

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around 84-87 percent, at most, being common. In addition, some ISPs will

havetraffic policies that limit maximum transfer rates further in the networks

beyond the exchange, and traffic congestion on the Internet, heavy loading on

servers and slowness or inefficiency in customers' computers may all

contribute to reductions below the maximum attainable. When a wireless

access point is used, low or unstable wireless signal quality can also cause

reduction or fluctuation of actual speed.

The choices the DSL modem make can also be either conservative, where the

modem chooses to allocate fewer bits per bin than it possibly could, a choice

which makes for a slower connection, or less conservative in which more bits

per bin are chosen in which case there is a greater risk case of error should

future signal-to-noise ratios deteriorate to the point where the bits-per-bin

allocations chosen are too high to cope with the greater noise present. This

conservatism, involving a choice of using fewer bits per bin as a safeguard

against future noise increases, is reported as the signal-to-noise ratio ''margin''

or ''SNR margin''. The telephone exchange can indicate a suggested SNR

margin to the customer's DSL modem when it initially connects, and the

modem may make its bits-per-bin allocation plan accordingly. A high SNR

margin will mean a reduced maximum throughput, but greater reliability and

stability of the connection. A low SNR margin will mean high speeds,

provided the noise level does not increase too much; otherwise, the connection

will have to be dropped and renegotiated (resynced). ADSL2+ can better

accommodate such circumstances, offering a feature termed ''seamless rate

adaptation'' (SRA), which can accommodate changes in total link capacity

with less disruption to communications.

Vendors may support usage of higher frequencies as a proprietary extension to

the standard. However, this requires matching vendor-supplied equipment on

both ends of the line, and will likely result in crosstalk problems that affect

other lines in the same bundle. There is a direct relationship between the

number of channels available and the throughput capacity of the ADSL

connection. The exact data capacity per channel depends on the

modulation method used.

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ADSL initially existed in two versions (similar to VDSL), namely CAP and

DMT. CAP was the ''de facto'' standard for ADSL deployments up until 1996,

deployed in 90 percent of ADSL installs at the time. However, DMT was

chosenfor the first ITU-T ADSL standards, G.992.1 and G.992.2 (also called

''G.dmt'' and ''G.lite'' respectively). Therefore all modern

installations of ADSL are based on the DMT modulation scheme.

3.3 Interleaving and fast path

ISPs (rarely, users) have the option to use interleaving of packets to counter

the effects of burst noise on the telephone line. An interleaved line has a

depth, usually 8 to 64, which describes how many Reed-Solomon codeword

are accumulated before they are sent. As they can all be sent together, their

forward error correction codes can be made more resilient. Interleaving adds

latency as all the packets have to first be gathered (or replaced by empty

packets) and they, of course, all take time to transmit. 8 frame interleaving

adds 5 ms round-trip-time, while 64 deep interleaving adds 25 ms. Other

possible depths are 16 and 32.

"Fastpath" connections have an interleaving depth of 1, that is one packet is

sent at a time. This has a low latency, usually around 10 ms (interleaving adds

to it, this is not greater than interleaved) but it extremely prone to errors, as

any burst of noise can take out the entire packet and so require it all to be

retransmitted. Such a burst on a large interleaved packet only blanks part of

the packet, it can be recovered from error correction information in the rest of

the packet. A "fastpath" connection will result in extremely high latency on a

poor line, as each packet will take many retries.

3.4 Installation Problems

ADSL deployment on an existing plain old telephone service (POTS)

telephone line presents some problems because the DSL is within a frequency

band that might interact unfavourably with existing equipment connected to

the line. Therefore, it is necessary to install appropriate frequency filters at the

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customer's premises to avoid interference between the DSL, voice services

and any other connections to the line, for example in support of intruder

alarms "Red Care" being an example in the UK. This is desirable for the voice

service and essential for a reliable ADSL connection.

In the early days of DSL, installation required a technician to visit the

premises. A splitter or ''micro filter'' was installed near thedemarcation point,

fromwhich adedicated data line was installed. This way, the DSL signal is

separatedas close as possibletothe central office and is not attenuated inside

the customer's premises. However, this procedure was costly, and also caused

problems with customers complaining about having to wait for the technician

to perform the installation. So, many DSL providers started offering a "self-

install" option, in which the provider provided equipment and instructions to

the customer. Instead of separating the DSL signal at the demarcation point,

the DSL signal is filtered at each telephone outlet by use of a low-pass filter

for voice and a high-pass filter for data, usually enclosed in what is known as a

micro filter. This microfilter can be plugged by an end user into any 'phone

jack: it does not require any rewiring at the customer's premises.

Commonly, microfilters are only low-pass filters, so beyond them only low

frequencies (voice signals) can pass. In the data section, a microfilter is not

used because digital devices that are intended to extract data from the DSL

signal will, themselves, filter out low frequencies. Voice telephone devices

will pick up the entire spectrum so high frequencies, including the ADSL

signal, will be "heard" as noise in telephone terminals, and will affect and

often degrade the service in fax, data phones and modems. From the point of

view of DSL devices, anyacceptance of their signal by POTS devices mean

that there is a degradation of the DSL signal to the devices, and this is the

central reason why these filters are required.

A side effect of the move to the self-install model is that the DSL signal can be

degraded, especially if more than 5 voiceband (that is, POTS telephone-like)

devices are connected to the line. Once a line has had DSL enabled, the DSL

signal is present on all telephone wiring in the building, causing attenuation

and echo. A way to circumvent this is to go back to the original model, and

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install one filter upstream from all telephone jacks in the building, except for

the jack to which the DSL modem will be connected. Since this requires

wiring changes by the customer, and may not work on some household

telephone wiring, it is rarely done. It is usually much easier to install filters at

each telephone jack that is in use.

DSL signals may be degraded by older telephone lines, surge protectors,

poorly-designed micro filters, radio-frequency interference, electrical noise,

and by long telephone extension cords. Telephone extension cords are

typically made with small-gauge, multi-strand copper conductors which do

not maintain a noise-reducing pair twist. Such cable is more susceptible to

electromagnetic interference and has more attenuation than solid twisted-pair

copper wires typically wired to telephone jacks. These effects are especially

significant where the customer's phone line is more than 4km from the

DSLAM in the telephone exchange, which causes the signal levels to be lower

relative to any local noise and attenuation. This will have the effect of

reducing speeds or causing connection failures.

3.5Transport Protocols

ADSL defines three "Transmission protocol-specific transmission convergence

(TPS-TC)" layers:

* Synchronous Transport Module (STM), which allows the transmission of

frames of the Synchronous Digital Hierarchy (SDH)

* Asynchronous Transfer Mode (ATM)

* Packet Transfer Mode (starting with ADSL2, see below)

In home installation, the prevalent transport protocol is ATM. On top of ATM,

there are multiple possibilities of additional layers of protocols(two of them

are abbreviated in a simplified manner as "PPPoA" or "PPPoE"), with the all-

important TCP/IP at layer 4 of the OSI model providing the connection to the

Internet.

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22

Table 4:ADSL Standards

Standard name Common

name

Downstream

rate

Upstream rate

ITU

G.992.1

ADSL(G.

DMT)

8Mbit

/s

1.0Mbi

t/s

ITU

G.992.2

ADSL

Lite(G.Lit

e)

1.5M

bit/s

0.5Mbi

t/s

ITU

G.992.3/4

ADSL2 12Mb

it/s

1.0Mbi

t/s

ITU

G.992.3/4

Annex J

ADSL2 12Mb

it/s

3.5Mbi

t/s

ITU

G.992.3/4

Annex L

RE-

ADSL2

5Mbit

/s

0.8Mbi

t/s

ITU

G.992.5

ADSL2+ 24Mb

it/s

1.0Mbi

t/s

ITU

G.992.5

Annex L

RE-

ADSL2+

24Mb

it/s

1.0Mbi

t/s

ITU

G.992.5

Annex M

ADSL2+ 28Mb

it/s

3.5Mbi

t/s

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CHAPTER-4

Digital Subscriber Line Access Multiplexer

Figure 5: Siemens DSLAM SURPASS hiX 5625

A digital subscriber line access multiplexer (DSLAM, often

pronounced dee-slam) is a network device, often located in the telephone

exchanges of the telecommunications operators. It connects multiple customer

digital subscriber line (DSL) interfaces to a high-speed digital

communications channel using multiplexing techniques. By placing additional

DSLAMs at locations remote from the telephone exchange, telephone

companies provide DSL service to locations previously beyond effective

range.

4.1 Path taken by data to DSLAM

1.Customer premises: DSL modem terminating the ADSL, SHDSL or VDSL

circuit and providing LAN interface to single computer or LAN segment.

2.Local loop: the telephone company wires from a customer to the telephone

exchange or to a serving area interface, often called the "last mile" (LM).

3.Telephone exchange:

Main distribution frame (MDF): a wiring rack that connects outside subscriber

http://en.wikipedia.org/wiki/File:Outdoor_DSLAM.JPG

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lines with internal lines. It is used to connect public or private lines coming

into the building to internal networks. At the telco, the MDF is generally in

proximity to the cable vault and not far from the telephone switch.

xDSL filters: DSL filters are used in the telephone exchange to split voice from

data signals. The voice signal can be routed to a POTS provider or left unused

whilst the data signal is routed to the ISP DSLAM via the HDF (see next entry).

Handover distribution frame (HDF): a distribution frame that connects the last

mile provider with the service provider's DSLAM

DSLAM: a device for DSL service. The DSLAM port where the subscriber

local loop is connected converts analog electrical signals to data traffic

(upstream traffic for data upload) and data traffic to analog electrical signals

(downstream for data download).

4.2 Role of the DSLAM

Figure 6: xDSL Connectivity diagram

The DSLAM equipment collects the data from its many modem ports and

aggregates their voice and data traffic into one complex composite "signal"

via multiplexing. Depending on its device architecture and setup, a DSLAM

aggregates the DSL lines over its Asynchronous Transfer Mode (ATM), frame

relay, and/or Internet Protocol network (i.e., an IP-DSLAM using PTM-TC

Packet Transfer Mode - Transmission Convergence) protocol(s) stack.

The aggregated traffic is then directed to a telco's backbone switch, via an

access network (AN) also called a Network Service Provider (NSP) at up to

10 Gbit/s data rates.

http://en.wikipedia.org/wiki/File:XDSL_Connectivity_Diagram_en.svg

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The DSLAM acts like a network switch since its functionality is at Layer2 of

the OSI model. Therefore it cannot re-route traffic between multiple IP

networks, only between ISP devices and end-user connection points. The

DSLAM traffic is switched to a Broadband Remote Access Server where the

end user traffic is then routed across the ISP network to the Internet.

Customer-premises equipment that interfaces well with the DSLAM to which

it is connected may take advantage of enhanced telephone voice and data line

signaling features and the bandwidth monitoring and compensation

capabilities it supports.

A DSLAM may or may not be located in the telephone exchange, and may

also serve multiple data and voice customers within a neighborhood serving

area interface, sometimes in conjunction with a digital loop carrier. DSLAMs

are also used by hotels, lodges, residential neighborhoods, and other

businesses operating their own private telephone exchange.

In addition to being a data switch and multiplexer, a DSLAM is also a large

collection of modems. Each modem on the aggregation card communicates

with a single subscriber's DSL modem. This modem functionality is integrated

into the DSLAM itself instead of being done via an external device like a

traditional computer modem.Like traditional voice-band modems, a DSLAM's

integrated DSL modems usually have the ability to probe the line and to adjust

themselves to electronically or digitally compensate for forward echoes and

other bandwidth-limiting factors in order to move data at the maximum

connection rate capability of the subscriber's physical line.

This compensation capability also takes advantage of the better performance of

"balanced line" DSL connections, providing capabilities for LAN segments

longer than physically similar unshielded twisted pair (UTP) Ethernet

connections, since the balanced line type is generally required for its hardware

to function correctly. This is due to the nominal line impedance (measured in

Ohms but comprising both resistance and inductance) of balanced lines being

somewhat lower than that of UTP, thus supporting 'weaker' signals (however

the solid-state electronics required to construct such digital interfaces is more

costly)

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CHAPTER-5

CONCLUSION

Because of the extremely high speeds that VDSL can accommodate, it is

being looked at as a good prospective technology for accommodating high

bandwidth applications like VoIP telephony and even HDTV transmission,

which ADSL is not capable of. Another very useful feature of VDSL stems from

thefact that it uses 7 different frequency bands for the transmission of data.

The user then has the power to customize whether each frequency band

would be used for download or upload. This kind of flexibility is very nice in

case you need to host certain files that are to be downloaded by a lot of

people. The most major drawback for VDSL is the distance it needs to be

away from the telephone exchange. Because of this, ADSL is still preferable

unless you live extremely close to the telephone exchange of the company

that you are subscribed to. Due to the limitations of VDSL and its high price,

its expansion is not as prolific as that of ADSL. VDSL is only widespread in

countries like South Korea and Japan. While other countries also have VDSL

offerings, it is only handled from a few companies; mostly one or two in most

countries. In comparison, ADSL is very widely used and all countries that offer

high speed internet offer ADSL. Hence VDSL is faster than ADSL and is not

widespread as ADSL. But still ADSL is better for homes that are much farther

from the DSLAM.

ADSL was born of the need for speed coupled with the desire for low cost

dedicated remote network access. There is no doubt that ADSL will

revolutionize the way we see the World Wide Web, and quite possibly

witness the demise of home entertainment as we know it. As the phoenix

from the flames we will see ADSL emerge heralding the coming of a new age

of remote multimedia. There is little doubt that ADSL will be around for a long

time to come, albeit under another name.

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If we are to truly realise the potential of the cyberspace concept we will need

to access it with as much convenience as turning on the television. With the

internet influencing our lives more and more each day, it will be high speed

ADSL connections that power the revolution. In the future people will view

ADSL like they view cable TV. That such a small object as an ADSL card may

wield such an influence over our lives may seem a little unbalanced, or is that

asymmetric

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BIBILOGRAPHY

References:

1. . Thomas; E. Gray (January 2001), RFC 3037: LDP Applicability, IETF2. de Ghein, Luc, MPLS Fundamentals, pp. 249326

3. Raza et al., Online routing of bandwidth guaranteed paths with local restoration usingoptimized aggregate usage information, IEEE-ICC 2005, retrieved 2006-10-27.

4. "Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice" by JohnEvans, Clarence Filsfils (Morgan Kaufmann, 2007, ISBN 0-12-370549-5)

5. Rick Gallaher's MPLS Training Guide (ISBN 1932266003).

6. S. Bryant; P. Pate (March 2005), RFC 3985: Pseudo Wire Emulation Edge-to-Edge (PWE3)Architecture, IETF

7. de Ghein, Luc, MPLS Fundamentals, pp. 249326.8. "AT&TFrame Relay and IP-Enabled Frame Relay Service (Product Advisor)", Research

and Markets, June 2007.

Websites:

1. www.google.com

2. www.wikipedia.com

3. www.networkworld.com

4. www.protocols.com

5. www.alttc.bsnl.co.in

6. www.itu.int

Text book

Telecommunication and switching systems and networks by thiagarajan viswanathan

http://www.google.com/http://www.google.com/http://www.wikipedia.com/http://www.wikipedia.com/http://www.networkworld.com/http://www.networkworld.com/http://www.protocols.com/http://www.protocols.com/http://www.alttc.bsnl.co.in/http://www.alttc.bsnl.co.in/http://www.itu.int/http://www.itu.int/http://www.itu.int/http://www.itu.int/http://www.itu.int/http://www.alttc.bsnl.co.in/http://www.protocols.com/http://www.networkworld.com/http://www.wikipedia.com/http://www.google.com/