1

ASYMMETRIC DIGITAL SUBSCRIBER LINE

A Project Report

Presented To

Mr. Fahrul Hakim AyobCommunications Technology and Networking Department

Faculty of Computer Science and Information Technology

University Putra Malaysia

In Partial Fulfillment

Of the Requirements for Advanced Computer Network (SAK5306) Course Subject

For the Degree of Master

By

Che Rohani Bt. Ishak (GS12895)

Saifuddin Bin Samsuddin (GS09785)

Siti Ruzaimah Bt. Ghazali (GS12557)

Tengku Mohd Dzaraif Bin Raja Abdul Kadir (GS10805)

August 2003

TABLE OF CONTENT

Page

1.0 Introduction 3

2.0 History of ADSL 5

3.0 ADSL Technology 6

3.1 System Architecture 7

3.1.1 System Reference Model 11

3.2 Modulation Technique 12

3.3 Different Types of ADSL 13

3.3.1 Full-Rate ADSL 13

3.3.2 G-Lite ADSL 13

3.4 Bandwidth 14

3.5 Connectors and Wiring Diagram 16

3.5.1 Connector Types 16

3.5.2 Wiring Diagram 18

4.0 Benefit 23

5.0 Problem 24

- Copper Loop Quality 24

6.0 Conclusion 25

Glossary 26

References 29

2

1. INTRODUCTION

Internet has become the most important tool in everyone life and it had changed

the way of lives for communication and interaction between family and friends. New

real-time applications such as video conferencing, peer to peer or multimedia

communications require high bandwidth to allow smooth transmission of voice and

video. The slant toward such multimedia traffic has far outstripped the capacity of the

current consumer-level solutions for Internet access such as high-speed modems and

ISDN (Integrated Services Digital Network).

There are several high-speeds or broadband solutions have been introduced to

extend the high-speed network solutions up to customer premise/home. These solutions

included cable modems, satellite communications, UHF communications (Ultra High

Frequency) and also DSL solutions (Digital Subscriber Line). Cable modems feature a

very high bandwidth, up to 30Mbps; however, a key restriction is that this bandwidth is

shared by as many as 500 to 2000 users connected to the same cable line. During times of

congestion, users may see significant degradation in performance. For satellite or UHF

communications (cable TV communications) the network is geared toward delivery only,

one-way communication and it will require support from other connection for the uplink

connection. These solutions are quite costing and required a new infrastructure.

This paper will focus on ADSL (Asymmetric Digital Subscriber Line), a new

broadband communication technology that creates high-speed access to the Internet and

remote networks using the ordinary phone lines present in your home. This exciting

technology not only helps to overcome the bandwidth limitation to customer but also

save the cost since it is just using the existing infrastructure i.e. two wire telephone lines.

It is seen to manipulate broadband markets where it will provide connection to almost

every home user.

3

To date there are many forms of DSL. A few of the forms that are currently in use

or development around the world are listed here:

  Service Downstream UpstreamADSL Asymmetric DSL 2M to 384k 256k to 128kHDSL High-bit-rate DSL 1.5M 1.5MSDSL Single-line DSL 1.5M 1.5MVDSL Very-High DSL 13M to 52M 1.5M to 2.3MIDSL ISDN DSL 144k 144kRADSL Rate Adaptive DSL 512k 278kUDSL Universal DSL 1M to 384k 384k to 128k

Table 1

4

2. HISTORY OF ADSL

The evolution of the ADSL technology has been started since the year 1985 and it is

predicted that ADSL will continue to increase and manipulate the world broadband

market (refer to Figure 1).

1985 - Bell Labs discovers a new way to make traditional copper wires support

new digital services - especially video-on-demand

1990 - Phone companies start deploying High-Speed DSL (HDSL) to offer T1

service on copper lines without the expense of installing repeaters - first between

small exchanges. Phone companies begin to promote HDSL for smaller and

smaller companies and ADSL for home Internet access.

1995 - Innovative companies begin to see ADSL as a way to meet the need for

faster Internet access

1998 - DMT was adopted by almost all vendors following ANSI T1.413 - issue 2

1999 - ITU-T produced UADSL G.992.2 (G.lite) and G.922.1 (G.full)

5

Figure 2: Broadband Communications Evolution

3. ADSL TECHNOLOGY

ADSL is asymmetrical, which means it provides higher transmission rates in the

downstream transmission than the upstream transmission. Although this asymmetry

sound unusual for a data transmission scheme, it is actually well suited to typical client

network traffic, where they send smaller data and expect to receive voluminous data from

the Internet (based on the web applications). ADSL refers to a modulation scheme used

to deliver network traffic to a customer's residence using the same copper twisted-pair

wiring used for voice and ISDN service. It coexists with both services, while offering 6 to

8Mbps speeds downstream and up to 640kbps upstream.

ADSL divides available bandwidth of a single copper-loop is into three parts. See

Figure 2. The first band normally between 0 and 25KHz, is used for normal telephone

communications in the 0 to 4 kHz range; whilst the rest is used to as a guard band to

separate voice from data channel. The second band, between 25 to 200KHz is used for

upstream communication. The third band will use 200KHz to 1MHz band for the

downstream communication.

6

Figure 2: Frequency Spectrum of ADSL

3.1 SYSTEM ARCHITECTURE

The ADSL Forum develops technical guidelines for architectures, interfaces, and

protocols for telecommunications networks incorporating ADSL transceivers. The overall

network diagram below describes the network elements incorporated in multimedia

communications, shows the scope of the Forum's work, and suggests a group of transport

configurations ADSL will encounter as networks migrate from Synchronous Transfer

Mode (STM) to Asynchronous Transfer Mode (ATM).

7

At the consumer end, a remote ADSL Transceiver Unit (ATU-R) is placed at the

customer’s site and configured as needed to support voice, data and video. If the location

is a high-rise building with multiple offices and apartments, or a campus with various

data needs, the ATU-R can be equipped with additional functionality such as bridging,

routing or multiplexing.

At the exchange end, a Digital Subscriber Line Access Multiplexer (DSLAM) and

ADSL Transceiver Unit (ATU-C) is installed. A single DSLAM can handle and route

traffic from multiple ATU-R installations, keeping the cost low because it is shared

among all service users. The existing telecommunications network then carries the data to

the destination, such as a branch office, again going through a DSLAM and ATU-R at the

receiving end. This is depicted in Figure 4.

A key characteristic of ADSL modems compared to traditional modems is that the

modems must be physically connected by the copper loop, rather than at either end of a

switched telephone connection; thus, one modem must usually reside at the telephone

company's switching station, and the other in the user's residence.

8

Figure 3: Home Connectivity Using ADSL

For Video-On-Demand applications, MPEG-compressed video streams typically

require 1.5Mbps of bandwidth for VHS quality. Thus, as many as four video streams can

be delivered simultaneously over an ADSL link, or one broadcast-quality 6Mbps MPEG-

2 stream. The video can then be decoded using a set-top box. (Veeneman, 838)

Once in the home, ADSL traffic can potentially be carried over the existing phone

wires. One proposal suggests a multi-carrier modulation system using the bandwidth

available over 1.5MHz (Chow, 456). This system would allow multiple computers and

set-top boxes to share the single ADSL transceiver, as well as continue to allow use of

POTS.

9

Network traffic can be transmitted using a variety of methods--ATM has been fingered

as a possible protocol, especially with respect to the transmission of real-time traffic such

as video and voice. For this reason, ADSL supports transmission rates compatible with

ATM.

10

3.1.1 SYSTEM REFERENCE MODEL

ADSL System reference model describes the basic blocks of an ADSL-system.

The decomposed and routed data from the access module, is connected to an ATU-C

(ADSL Transceiver Unit - Central Office) in which the data will be converted into analog

signals. The analog signals are then carried with POTS signals to remote end. ATU-C

also receives and decodes data coming from customers premises send by ATU-R

(remote).

The splitter either combines or separates the signals depending on the direction of the

transmission. It protects MTS from voice-band interference generated by both ATU's and

on the other hand it protects ATU's from MTS-related signals.

  

  

11

3.2 MODULATION TECHNIQUES

Most of the ADSL implementation originally using carrierless Amplitude/phase

(CAP) but later Discrete Multitone (DMT) is used due to its higher throughput and

greater resistance to adverse line conditions. It effectively compensates for widely

varying line noise conditions and quality levels

CAP is a modulation technique that is similar to QAM but the carrier signal is

eliminated. The technique is more complex than QAM and has not been standardized.

DMT combines QAM and FDM and this technique were standardized by ANSI.

12

3.3 DIFFERENT TYPES OF ADSL

3.3.1 Full-rate ADSL

i. Full-rate ADSL boasts data rates ranging from 1.5 to 8 Megabits per

second “downstream” from the Internet to your computer

ii. “Upstream” data rates from your computer to the Internet are as high

as 1 Mbps

iii. Potential data rates decrease with increased distance from the phone

company’s CO (central office)

iv. Costs for the service are more expensive than the new, lower data rate

“G.Lite” ADSL

3.3.2 G-Lite ADSL

i. G.Lite ADSL is a scaled-down version that delivers up to 1.5 Mbps

downstream and 384 Kbps up

ii. Service providers will offer slower rates for lower prices

iii. Less expensive than full-rate ADSL

iv. Easier to install

Full-rate ADSL requires a splitter, to be installed on your phone line where it enters

your home in order to separate the voice service from the data service. Whereas G.Lite

ADSL will not usually require a splitter, although some homes with problematic wiring

or certain types of telephones will require one.

13

3.4 BANDWIDTH

There are ten classes for ADSL transmission speeds. Classes 1-4 were developed

with multiple channels of digital video as the primary application, and feature only low-

speed upstream channels used for control and signaling. Classes 5-10 reflect the data-

aware ADSL speeds.

Class Downstream Upstream

1 6.144Mbps 64kbps

2 4.608Mbps 64kbps

3 3.072Mbps 64kbps

4 1.536Mbps 64kbps

5 6.2Mbps 576kbps

6 3.1Mbps 384kbps

7 1.544Mbps 160kbps

8 768kbps 64kbps

9 384kbps 32kbps

10 160kbps 16kbps

Table 2

(Veeneman, 838-840)

14

The differing lengths of copper loops results in the following changes in useful

bandwidth:

DistanceDownstream

speedNotes

18,000 feet 1.544Mbps 24 gauge wire

16,000 feet 2.048Mbps

12,000 feet 6.312Mbps

9,000 feet 8.448MbpsAverage line

length for U.S. customers.

Table 3

These estimates reflect optimal conditions. The actual bandwidth varies

significantly depending on the particular hardware implementation used and the line

conditions encountered.

15

3.5 CONNECTORS AND WIRING DIAGRAM

3.5.1 CONNECTOR TYPES

RJ-11 Broadband/Telephone Plug

The US style RJ-11 plug is a 4-pin version

of the RJ-45 pictured below. It is the

smallest in size and is used in the UK for

DSL/Broadband Internet connections (RJ-

11 to RJ-11).

British (Telecom) Plug

The familiar British telephone plug used in

over 30 countries around the world. Any

analogue device that operates over a

telephone line will be connected using this

plug. You'll often find an RJ-11 plug on

one end, and a BT plug on the other (RJ-11

to BT).

USB Type A (Computer)

Universal Serial Bus (USB) is the most

popular way of connecting peripherals to

your computer. To connect most devices,

you'll require a type A to B cable (often

supplied with the product).

USB Type B (Peripherals)

The other end of the USB wire features a

square shape plug designed to connect to

peripherals such as your USB DSL modem

or router.

RJ-45 Ethernet Network (Crimped Plug)

The RJ-45 connector, featuring 8 pins, is

the big brother of the RJ-11. It's used for

16

data communications, specifically Local

Area Networks (LANs). Cables can be

either straight (for normal use between a

hub and a computer) or crossed (for use

between two hubs or switches). Each

computer requires a Network Interface

Card (NIC) to connect to the network.

RJ-45 Ethernet Network (Moulded Plug)

The moulded RJ-45 plug shown to the left

performs exactly the same purpose as the

crimped version above. Professionally

constructed cables are usually moulded by

a machine instead of crimped using a

special device called a "crimping tool".

17

3.5.2 WIRING DIAGRAM

Basic diagrammatic scenarios are based upon:

Internet connection via a USB Modem

Internet connection via an Ethernet router/modem

Connecting additional telephone sockets

Beware of a certain amount of software configuration must also be carried out before

computers and network peripherals are able to operate or communicate with each other.

This includes software driver installation for USB modems and the correct assignment of

IP addresses and related parameters for Ethernet networks.

Figure : Key to Cable Types

USB ModemThe easiest and most popular way to get a single computer online with is via a USB modem. The process involves connecting the USB modem to the DSL side of your micro-filter, and your computer to the USB modem using a standard type A to B USB cable. Software installation procedure will vary depending upon the equipment purchased.

18

Many users choose to share their USB Broadband connection using software such as

Microsoft Internet Connection Sharing (ICS). In this scenario, the computer will act as a

gateway for other computers to access the Internet via a Local Area Network (LAN).

The same concept can be extended to wireless network cards instead of the more

restrictive fixed approach above. This configuration is often referred to as "ad-hoc

networking mode" with the sharing computer operating in "infrastructure mode". Most

users will find that sharing their USB connection over a wired network is adequate.

19

Ethernet Router & Local Area NetworkThe following diagrams show sample configurations for Internet access via an Ethernet

router/modem. Many routers feature a 2, 4 or 8 port inbuilt Ethernet hub or switch (a

device used to connect computers together). In this scenario, computers can be connected

directly to the router. Each computer is wired using a standard Ethernet cable with one

end connected to a spare port on the inbuilt hub/switch and the other end connected to the

computers network card.

If your Ethernet router only has 1 network port, or you want to connect more devices to

the network than there are available ports, a Ethernet switch can be used in combination

with a crossover cable to extend the size of your network.

20

Micro-Filters and Additional Telephone SocketsMicro-filters must be used to separate the two different frequency bands used over your

telephone line (voice and data) and prevent your analogue devices from interfering with

the Broadband frequency ranges used by your modem/router.

Simple method: Walk around your house and count how phones are plugged into a phone

socket (on the same line) and order the same number of micro-filters. Simply unplug each

phone, plug them into the splitter and reconnect to the phone line.

21

Cheaper method: Buy a single micro-filter and plug this into your master socket and run

all the phone extensions off the phone side of the micro-filter. Finally, run an extension

from the ADSL side of the splitter to where you want to use your ADSL modem.

22

4. BENEFITS

ADSL technology is far more advantageous than other access technologies

currently available. The benefits of ADSL include:

Connectivity

Simultaneous Internet and telephone/fax capabilities over a single telephone line.

A user is always connected and there is no need to dial up.

Speed

ADSL can endure the data rate necessary to handle all kinds of applications, such

as very high fast data transfer and broadcast video: 1.544 to 9 Mbps downstream, 16Kbps

to 1.544 Mbps upstream.

Cost Effectiveness

Because of the usage of existing copper pairs, the ADSL is a very cost-effective

solution for residential users and small businesses.

Reliability

ADSL operates over the copper-based telephone network that is one of the most

robust and proven infrastructures.

23

5. PROBLEM

Copper Loop Quality

Several factors may affect the throughput of a twisted-pair copper loop:

Loop length

The length of the copper loop between the central station and the residence is the

most prominent factor in available throughput. Signals are attenuated by an amount

proportional to the loop length. In addition, the attenuation is a function of the frequency,

such that higher frequencies are attenuated more than lower frequencies. (Aas)

Bridged Taps

Lengths of non-terminated twisted-pair cable connected in parallel to the primary

pair.

Ham and AM radio

These radio transmissions fall within the spectrum used by ADSL and can be a severe

disruption to the signal.

Crosstalk

Interference from adjacent wires in the feeder trunks running to the neighborhood.

Increasing the transmission power cannot compensate for this distortion, since the noise

from the higher-powered adjacent lines would also grow in proportion.

Wire Gauge

The effective range and throughput can be shortened by higher-gauge (smaller)

wire. Some copper loops user different gauge wires at different points--this can cause

reflections in the signal, effectively attenuating some frequencies. (Minoli, 341)

24

6. CONCLUSION

ADSL is poised to become the next revolutionary leap in remote data access

technologies. It promises very high performance without a corresponding high cost, and

does not require a large investment in infrastructure upgrades.

ADSL increase the capacity of copper cable to support high-speed broadband data

such as video conferencing, multi-media, high-speed Internet access and interactive

services. Besides giving high bandwidth it is able to access almost every place in the

world that provides phone connectivity.

25

GLOSSARY

ADSL Asymmetric Digital Subscriber Line STM Synchronous Transfer Mode

ATM Asynchronous Transfer Mode TE Terminal Equipment

OS Operations System See System Reference Model for reference

PDN Premises Distribution Network point definitions

SM Service Module

ATU-C ADSL Transmission Unit at the network end. The ATU-C may be

integrated within an Access Node

ATU-R ADSL transmission Unit at the customer premises end. The ATU-R

may be integrated within an SM

Access Node Concentration point for Broadband and Narrowband data. The Access

Node may be located at a Central Office or a remote site. Also, a

remote Access Node may subtend from a central access node

B Auxiliary data input (such as a satellite feed) to Service Module (such

as a Set Top Box)

Broadcast Broadband data input in simplex mode (typically broadcast video)

Broadband

Network

Switching system for data rates above 1.5/2.0 Mbps

Loop Twisted-pair copper telephone line. Loops may differ in distance,

diameter, age, and transmission characteristics depending on network.

Narrowband

Network

Switching system for data rates at or below 1.5/2.0 Mbps

POTS Plain Old Telephone Service

POTS-C Interface between PSTN and POTS splitter at network end

POTS-R Interface between phones and POTS splitter at premises end

PDN Premises Distribution Network: System for connecting ATU-R to

Service Modules. May be point-to-point or multipoint; may be passive

wiring or an active network. Multipoint may be a bus or star

PSTN Public Switched Telephone Network

SM Service Module: Performs terminal adaptation functions. Examples are

set top boxes, PC interfaces, or LAN router

26

Splitter Filters which separate high frequency (ADSL) and low frequency

(POTS) signals at network end and premises end. The splitter may be

integrated into the ATU, physically separated from the ATU, or divided

between high pass and low pass, with the low pass function physically

separated from the ATU. The provision of POTS splitters and POTS-

related functions is optional

T-SM Interface between ATU-R and Premises Distribution Network. May be

same as T when network is point-to-point passive wiring. An ATU-R

may have more than one type of T-SM interface implemented (e.g., a

T1/E1 connection and an Ethernet connection). The T-SM interface

may be integrated within a Service Module

T Interface between Premises Distribution Network and Service Modules.

May be same as T-SM when network is point-to-point passive wiring.

Note that T interface may disappear at the physical level when ATU-R

is integrated within a Service Module

U-C Interface between Loop and POTS Splitter on the network side.

Defining both ends of the Loop interface separately arises because of

the asymmetry of the signals on the line

U-C2 Interface between POTS splitter and ATU-C. Note that at present ANSI

T1.413 does not define such an interface and separating the POTS

splitter from the ATU-C presents some technical difficulties in

standardizing the interface

U-R Interface between Loop and POTS Splitter on the premise side

U-R2 Interface between POTS splitter and ATU-R. Note that at present ANSI

T1.413 does not define such an interface and separating the POTS

splitter from the ATU-R presents some technical difficulties in

standardizing the interface

VA Logical interface between ATU-C and Access Node. As this interface

will often be within circuits on a common board, the ADSL Forum

does not consider physical VA interfaces. The V interface may contain

STM, ATM, or both transfer modes. In the primitive case of point-to-

27

point connection between a switch port and an ATU-C (that is, a case

without concentration or multiplexing), then the VA and VC interfaces

become identical (alternatively, the VA interface disappears)

VC Interface between Access Node and network. May have multiple

physical connections (as shown) although may also carry all signals

across a single physical connection. A digital carrier facility (e.g., a

SONET or SDH extension) may be interposed at the VC interface when

the access node and ATU-Cs are located at a remote site. Interface to

the PSTN may be a universal tip-ring interface or a multiplexed

telephony interface such as specified in Bellcore TR-08 or TR-303. The

broadband segment of the VC interface may be STM switching, ATM

switching or private line type connections

REFERENCES

28

1. Dale Veeneman, Robert Olshansky. GTE Laboratories Incorporated. ADSL for Video and Data Services. IEEE Communications Conference. 1995. pp. 837-841.

2. Seiichi Yamano. NTT Transmission Systems Laboratories. The Range of HDSLs and ADSLs in NTT's Local Networks. IEEE Communications Conference. 1994. pp. 444-450.

3. Walter Y. Chen, David L. Waring. Bell Communications Research. ADSL Noise Environment and Potential System Performance. IEEE Communications Conference. 1994. pp. 451-455.

4. Peter S. Chow, John M. Cioffi. Amati Communications Corporation. A Multi-drop In-house ADSL Distribution Network. IEEE Communications Conference. 1994. pp. 456-460.

5. http://www.epl.co.uk/timing.htm . ADSL Timescale

29