ASYMMETRIC DIGITAL SUBSCRIBER LINE
A Project Report
Mr. Fahrul Hakim Ayob
Communications 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
Che Rohani Bt. Ishak (GS12895)
Saifuddin Bin Samsuddin (GS09785)
Siti Ruzaimah Bt. Ghazali (GS12557)
Tengku Mohd Dzaraif Bin Raja Abdul Kadir (GS10805)
TABLE OF CONTENT
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
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.
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 Upstream
ADSL Asymmetric DSL 2M to 384k 256k to 128k
HDSL High-bit-rate DSL 1.5M 1.5M
SDSL Single-line DSL 1.5M 1.5M
VDSL Very-High DSL 13M to 52M 1.5M to 2.3M
IDSL ISDN DSL 144k 144k
RADSL Rate Adaptive DSL 512k 278k
UDSL Universal DSL 1M to 384k 384k to 128k
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)
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
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).
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.
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
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
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
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.
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.
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
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.
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
The differing lengths of copper loops results in the following changes in useful
18,000 feet 1.544Mbps 24 gauge wire
16,000 feet 2.048Mbps
12,000 feet 6.312Mbps
9,000 feet 8.448Mbps length for U.S.
These estimates reflect optimal conditions. The actual bandwidth varies
significantly depending on the particular hardware implementation used and the line
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
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
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
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".
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
The 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
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.
Ethernet Router & Local Area Network
The 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.
Micro-Filters and Additional Telephone Sockets
Micro-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.
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.
ADSL technology is far more advantageous than other access technologies
currently available. The benefits of ADSL include:
Simultaneous Internet and telephone/fax capabilities over a single telephone line.
A user is always connected and there is no need to dial up.
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.
Because of the usage of existing copper pairs, the ADSL is a very cost-effective
solution for residential users and small businesses.
ADSL operates over the copper-based telephone network that is one of the most
robust and proven infrastructures.
Copper Loop Quality
Several factors may affect the throughput of a twisted-pair copper loop:
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)
Lengths of non-terminated twisted-pair cable connected in parallel to the primary
Ham and AM radio
These radio transmissions fall within the spectrum used by ADSL and can be a severe
disruption to the signal.
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.
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)
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.
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 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 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
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-
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
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.
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