The White Paper Series

ADSL2+:
Revolutionizing the
Broadband Market

September 2005

Intelligent WAN Access Solutions

Copyright 2005 Quick Eagle Networks Inc. All rights reserved.

 Executive Summary

Overall, the demand for ADSL services continues to accelerate around the world.
While originally considered for use primarily in the residential and SOHO markets,
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

ADSL is becoming an important technology for the small business and branch office
market. As download speeds have increased and more bandwidth has become available,
small businesses and remote offices of larger organizations are starting to take advantage
of broadband and its ability to deliver streaming media, multi-media, and high-traffic business
applications.

Even though both residential and business users are taking advantage of the same
access technology, their access device requirements are very different. This white
paper will discuss the existing ADSL standards, ways of deployment, and differences in
residential and business-class ADSL CPE devices as well as the overall market trends
in the xDSL arena.

xDSL Market Status

According to a recent study by Infonetics Research, the broadband boom continues:

worldwide, revenue for broadband modems, routers, and gateways totaled $4.6 billion
in 2004, up 15% from 2003, and units totaled 73 million, up 74%.

“As xDSL outpaces growth in other forms of broadband access, xDSL CPE devices
become an even more significant proportion of the overall CPE market, said Richard
Webb, directing analyst of Infonetics Research and lead author of the report.

Future unit growth will be fuelled by the increased demand for “IP Video over DSL” and
“Voice over IP via DSL” applications.

xDSL Technologies

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 residential or business service subscribers. The term xDSL covers a number
of similar yet competing forms of DSL, including ADSL, SDSL, MDSL, MHDSL, HDSL,
RADSL, and VDSL.

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 HDSL, MDSL, as well as MSDSL are so called symmetric technologies, whereas
downstream and upstream data rates equal each other. ADSL, ADSL2, and ADSL2+
technology is asymmetric. It allows more bandwidth downstream from the service
provider’s central office to the customer site than upstream from the user to the central
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

office. This asymmetry, combined with always-on access (which eliminates call setup),
makes ADSL ideal for Internet applications, video conferencing, and remote LAN
access.

xDSL is drawing significant attention from carriers and service providers because it
promises to deliver high-bandwidth data rates to dispersed locations with relatively
small changes to the existing telecommunications / networking infrastructure. Currently
the primary focus in xDSL is the development and deployment of ADSL and VDSL
technologies and architectures.

Overview of ADSL Standards

ADSL Standard

The first ADSL standard was approved by the American National Standards Institute
(ANSI) in 1995. It supported data rates up to 6.1 Mbps (ANSI Standard T1.413). To
reflect European requirements, the European Technical Standards Institute (ETSI)
established an Annex to T1.413. In 2001 the standard was expanded to include a
multiplexed interface at the premise end, protocols for configuration and network management,
and other improvements. These enhancements were then submitted to the international
standards body, the ITU-T, to develop the international standards for ADSL. The ITU-T
standards for ADSL are most commonly referred to as G.lite (G.992.2) and G.dmt
(G.992.1). Having an international standard has aided in moving towards vendor
interoperability and service provider acceptance, further increasing deployment, and
ultimately availability to the end user.

Asymmetric Digital Subscriber Line (ADSL), is a modem technology that converts

existing twisted-pair telephone lines into access paths for multimedia and high-speed
data communications. ADSL can transmit up to 8 Mbps to a subscriber (downstream
rate), and as much as 1 Mbps in both directions (upstream rate).

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 An ADSL circuit connects an ADSL modem on each end of a twisted-pair telephone
line, creating three information channels -- a high speed downstream channel, a medium
speed duplex channel, depending on the implementation of the ADSL architecture, and
a POTS (Plain Old Telephone Service) or an ISDN channel.
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

The POTS / ISDN channel is split off from the digital modem by filters, thus guaranteeing
uninterrupted POTS / ISDN, even if ADSL fails. 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.

ADSL2 Standard

In July 2002, the ITU completed G.992.3 and G.992.4 , two new standards for ADSL
technology collectively called "ADSL2". ADSL2 adds new features and functionality
targeted at improving performance and interoperability, and adds support for new
applications, services, and deployment scenarios. Among the changes are improvements
in data rate and reach performance, rate adaptation, diagnostics, and stand-by mode,
to name a few.

ADSL2 achieves downstream and upstream data rates of about 12 Mbps and 1 Mbps
respectively, depending on loop length and other factors. ADSL2 accomplishes this by
improving modulation efficiency, reducing framing overhead, achieving higher coding
gain, improving the initialization state machine, and providing enhanced signal
processing algorithms. As a result, ADSL2 mandates higher performance for all
standard-compliant devices.

ADSL2 provides better modulation efficiency by mandating four-dimensional, 16-state

trellis-coded and 1-bit quadrature amplitude modulation (QAM) constellations, which
provide higher data rates on long lines where the signal-to-noise ratio (SNR) is low. In
addition, receiver-determined tone reordering enables the receiver to spread out the
non-stationary noise due to AM radio interference to get better coding gain from the
Viterbi decoder.

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 On longer phone lines, ADSL2 will provide a data rate increase of 50 kbps compared
to ADSL for upstream and downstream; a significant increase for those customers who
need it most. This data rate increase results in an increase in reach of about 600 feet,
which translates to an increase in coverage area of about 6%, or 2.5 square miles.
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

Figure 1: Distance improvement via ADSL2 implementation

Determining the cause of problems in ADSL service has at times been a challenging
obstacle in ADSL deployments. To tackle the problem, ADSL2 transceivers have been
enhanced with extensive diagnostic capabilities. These diagnostic capabilities provide
tools for trouble resolution during and after installation, performance monitoring while in
service, and upgrade qualification.

First-generation ADSL transceivers operate in full-power mode day and night, even
when not in use. With an increasing number of deployed ADSL modems, a significant
amount of electricity can be saved if the modems engage in a standby / sleep mode
just like computers. To address these concerns, the ADSL2 standard brings in two
power management modes that help reduce overall power consumption while maintaining
ADSL's "always-on" functionality for the user.

Another obstacle for ADSL deployment was the fact that telephone wires are bundled
together in multi-pair binders, containing 25 or more twisted pairs at a time. As a result,
electrical signals from one pair can electro-magnetically couple onto adjacent pairs.

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 This phenomenon is known as “crosstalk” was addressed in the ADSL2 implementation
by seamlessly adapting the data rate in real-time. This new innovation, called seamless
rate adaptation (SRA), enables the ADSL2 system to change the data rate of the
connection while in operation without any service interruption or bit errors. ADSL2 simply
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

detects changes in the channel conditions-for example, a local AM radio station turning
off its transmitter for the evening, and adapts the data rate to the new channel condition
transparently to the user.

Data rates to homes and businesses can be significantly increased by bonding multiple
phone lines together. To enable bonding, the ADSL2 standards support the ATM
Forum's inverse multiplexing for ATM (IMA) standard (af-phy-0086.001) developed for
traditional ATM architectures. Through IMA, ADSL2 chipsets can bind two or more
copper pairs in an ADSL link. The result is far greater flexibility with downstream data
rates.

Other benefits of ADSL2 are:

- Support for channelized Voice over DSL

- Improved interoperability
- Reduced start-up time for the modem to 3 seconds
- Support of all digital modes, adding 256 kbps of upstream data rate
- Support of packet-based services such as Ethernet over ADSL2

ADSL2+ Standard

ADSL2plus, or ADSL2+, reached consent at the ITU in January 2003, joining the
ADSL2 standards family as G.992.5. The ADSL2+ recommendation doubles the
downstream bandwidth, thereby increasing the downstream data rate on telephone
lines shorter than about 5,000 feet.

While the first two members of the ADSL2 standards family specify a downstream
frequency band up to 1.1 MHz and 552 kHz respectively, ADSL2+ specifies a
downstream frequency up to 2.2 MHz (see Figure 2). The result is a significant
increase in downstream data rates on shorter phone lines (see Figure 3). ADSL2+
upstream data rate is about 1 Mbps, depending on loop conditions.

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In t e l l i g e n t W A N A c c e s s S o l u t i o n s

Figure 2: ADSL2+ doubles downstream bandwidth

Figure 3: ADSL2+ doubles maximum downstream data rate

ADSL2+ can also be used to reduce crosstalk. ADSL2+ provides the capability to use
only tones between 1.1 MHz and 2.2 MHz by masking the downstream frequencies
below 1.1 MHz. This can be particularly useful when ADSL services from both the
central office (CO) and a remote terminal (RT) are present in the same binder as they
approach the end user’s location. The crosstalk from the ADSL services from the
RT onto the lines from the CO can significantly impair data rates on the line from the
CO. ADSL2+ can correct this problem by using frequencies below 1.1 MHz from the
central office to the remote terminal, and frequencies between 1.1 MHz and 2.2 MHz
from the remote terminal to the end user’s premise.

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 This will eliminate most of the crosstalk between the services and preserve data rates
on the line from the central office.

ADSL Standard Annexes

In t e l l i g e n t W A N A c c e s s S o l u t i o n s

ADSL standards also include annexes that specify ADSL operation for particular
applications and regions around the world. In general, the annexes specify subcarriers
(or tones) and their associated transmission power levels used for upstream and
downstream transmission. Enclosed you will find a brief overview of the different
annexes:

ANNEX ENVIRONMENT ADSL ADSL2 ADSL2+

A POTS YES YES YES
B ISDN YES YES YES
C TCM-ISDN YES YES YES
I (ADSL) TCM-ISDN YES YES YES
I (ADSL2) POTS YES NO NO
J ISDN NO YES YES
L (READSL2) POTS NO YES NO
M (ADSL2+) POTS NO YES YES

ADSL CPE Equipment - Business-class vs. Residential

The first thing that comes to mind when you hear the keyword “DSL” or “ADSL” is the
little modem that normally comes with your DSL service package at home. However,
while originally considered for use primarily in the residential and SOHO markets,
ADSL is becoming an important technology for the small business and branch office
market. As download speeds have increased and more bandwidth has become
available, small businesses and remote offices of larger organizations are starting to take
advantage of broadband and its ability to deliver streaming media, multi-media, and
high-traffic business applications.

Even though both residential and business users are taking advantage of the same
access technology, their access device requirements are very different. So what are
the main features that you should take into consideration when looking for a business-

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 class ADSL access device?

Interoperability and Functionality

Business-class ADSL products differ from residential gateways quite dramatically:

In t e l l i g e n t W A N A c c e s s S o l u t i o n s

While residential devices are most likely nothing else than a simple modem, business-
class ADSL devices come often as a combination of router with integrated modem,
therefore reducing the number of potential points of failure. In addition, it may be wise
to select an ADSL router that complies with all the main ADSL standards as described
before. In this case, you can migrate to the newer standards once they become
available from your service provider without having to “forklift-upgrade” your existing
equipment.

Security

One of the most important things to look out for when selecting an ADSL access device
for business purposes, it its security capabilities. Communicating in the residential
environment does not necessarily require indepth security features. However, when we
talk about your business communications, this view changes quickly. As a result, your
ADSL router should come with a stateful inspection firewall as normally used in high-
end routing equipment as well as different encryption methods if a wireless Local Area
Network (LAN) is part of the solution. As sensitive information is exchanged between
remote and/or home offices and the headquarters, ADSL routers with integrated VPN
capabilities allow users to make a tunnel with a remote site directly to secure the data
transmission among the connection.

Remote Management and Diagnostics

In a business environment, remote management and diagnostic capabilities play a far

bigger role than in the residential area. Uptime is essential for businesses and therefore
having management tools such as Telnet, CLI, FTP, Web GUI, and SNMPv3 at hand
are crucial. This holds true especially if you have no IT personnel at your remote office
or home office.

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 Quality of Service

As download speeds have increased and more bandwidth has become available, small
businesses and remote offices of larger organizations are starting to take advantage of
broadband and its ability to deliver streaming media, multi-media, and high-traffic business
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

applications. As these applications “compete” for bandwidth, a business-class ADSL

router should provide you with the capability to prioritize traffic based on the traffic
type. This feature is called “Quality of Service” (QoS). The QoS capabilities give you
full control over which types of outgoing data traffic should be given priority by the
ADSL router, ensuring important data like customer information or management
information move through the router at lightning speed, even under heavy load. The
QoS features should be configurable by source IP address, destination IP address,
protocol, and port.

Voice over IP

To enable an easy and cost-efficient transition from traditional telephone systems to

nowadays popular Voice over IP (VoIP) systems, you should select a ADSL router that
enables you to leverage your existing analog phone equipment, but still use the
Internet to make and receive phone calls.

ADSL routers can support cost-effective, toll-quality voice calls over the Internet by
integrating FXS ports into the device. In this case, functions such as call waiting,
silence suppression, voice activity detection (VAD), comfort noise generation (CNG),
line echo cancellation, caller ID (Bell 202, V3) and more are available.

To support “Lifeline Support” you might want to select an ADSL router that in addition
integrates an RJ-11 FXO port for inbound and outbound calls transmitted through
PSTN. Here, the users can receive phone calls from PSTN while enjoying VoIP call
services at the same time. In addition, the device would automatically fallback to life-
line POTS to enable making normal phone calls when there is a power outage, or
when the Internet connection is down.

Quick Eagle Networks’ new DL700 ADSL2+ RouterTM and DL710 ADSL2+ RouterTM
address all these special requirements described above. Both routers are designed
specifically for the small business and remote office market.

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 Conclusion

Many carriers and Internet service providers are currently upgrading their network
infrastructure to integrate ADSL2+ as their new broadband standard offering. The
In t e l l i g e n t W A N A c c e s s S o l u t i o n s

increased bandwidth capabilities will further fuel the growth of ADSL as an access
technology in the remote office and small business market. This trend will change the
requirements of ADSL CPE devices dramatically as business have different feature
requirements than residential users. As a result, a new generation of all-in-one ADSL
gateways will enter the market soon.

About Quick Eagle Networks

Quick Eagle Networks, Inc. is a provider of intelligent WAN access solutions for Frame
Relay and IP networks, and the world leader in multilink access devices. The company's
product portfolio ranges from traditional CSU/DSUs, access multiplexers, multilink
access devices, bridges, WAN probes, to routers (NxT1/E1, ADSL, ADSL2, and
ADSL2+), providing expanded functionality for reduced cost at the LAN/WAN interface.
Founded in 1985 and recognized worldwide for its Digital Link and Quick Eagle brand
products, the company serves many of the world's leading enterprises and carriers
including Boeing, Wells Fargo, Bank of America, Citigroup, EDS, MCI, Sprint, British
Telecom, Deutsche Telekom, and France Telecom. Quick Eagle Networks is an ISO
9001:2000 certified company, with headquarters in Sunnyvale, California and sales and
distribution offices worldwide.

For more information about Quick Eagle’s full range of WAN access solutions visit our
website at www.quickeagle.com or email info@quickeagle.com.

Copyright 2005 Quick Eagle Networks. All rights reserved. Company and product names are trademark or registered trademark of
their respective owners. No part of this publication may be reproduced, photocopied, stored on a retrieval system, transmitted, or
translated into another language without the express written consent of Quick Eagle Networks, Inc. The information contained
herein is believed to be reliable but cannot be guaranteed to be complete or correct. Created 09/05 - Version 1.4

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