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I n 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

Copyright 2005 Quick Eagle Networks Inc. All rights reserved.

The White Paper Series

ADSL2+:

Revolutionizing theBroadband Market

September 2005


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

Even though both residential and business users are taking advantage of the sameaccess technology, their access device requirements are very different. This whitepaper 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 trendsin 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 billionin 2004, up 15% from 2003, and units totaled 73 million, up 74%.

As xDSL outpaces growth in other forms of broadband access, xDSL CPE devicesbecome an even more significant proportion of the overall CPE market, said RichardWebb, 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 andVoice over IP via DSL applications.

xDSL Technologies

Digital Subscriber Line (DSL) technology is a modem technology that uses existingtwisted-pair telephone lines to transport high-bandwidth data, such as multimedia andvideo, 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, whereasdownstream and upstream data rates equal each other. ADSL, ADSL2, and ADSL2+technology is asymmetric. It allows more bandwidth downstream from the serviceproviders central office to the customer site than upstream from the user to the centraloffice. This asymmetry, combined with always-on access (which eliminates call setup),makes ADSL ideal for Internet applications, video conferencing, and remote LANaccess.

xDSL is drawing significant attention from carriers and service providers because itpromises to deliver high-bandwidth data rates to dispersed locations with relativelysmall changes to the existing telecommunications / networking infrastructure. Currentlythe primary focus in xDSL is the development and deployment of ADSL and VDSLtechnologies 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). Toreflect European requirements, the European Technical Standards Institute (ETSI)

established an Annex to T1.413. In 2001 the standard was expanded to include amultiplexed interface at the premise end, protocols for configuration and network management,and other improvements. These enhancements were then submitted to the internationalstandards body, the ITU-T, to develop the international standards for ADSL. The ITU-Tstandards 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, andultimately availability to the end user.

Asymmetric Digital Subscriber Line (ADSL), is a modem technology that convertsexisting twisted-pair telephone lines into access paths for multimedia and high-speeddata communications. ADSL can transmit up to 8 Mbps to a subscriber (downstreamrate), 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 telephoneline, creating three information channels -- a high speed downstream channel, a mediumspeed duplex channel, depending on the implementation of the ADSL architecture, anda POTS (Plain Old Telephone Service) or an ISDN channel.

The POTS / ISDN channel is split off from the digital modem by filters, thus guaranteeinguninterrupted POTS / ISDN, even if ADSL fails. Downstream data rates depend on anumber of factors, including the length of the copper line, its wire gauge, presence of bridged taps, and cross-coupled interference. Line attenuation increases with linelength 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 ADSLtechnology collectively called "ADSL2". ADSL2 adds new features and functionalitytargeted at improving performance and interoperability, and adds support for newapplications, services, and deployment scenarios. Among the changes are improvementsin 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 byimproving modulation efficiency, reducing framing overhead, achieving higher codinggain, improving the initialization state machine, and providing enhanced signalprocessing algorithms. As a result, ADSL2 mandates higher performance for allstandard-compliant devices.

ADSL2 provides better modulation efficiency by mandating four-dimensional, 16-statetrellis-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. Inaddition, receiver-determined tone reordering enables the receiver to spread out thenon-stationary noise due to AM radio interference to get better coding gain from theViterbi decoder.


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On longer phone lines, ADSL2 will provide a data rate increase of 50 kbps comparedto ADSL for upstream and downstream; a significant increase for those customers whoneed 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.

Figure 1: Distance improvement via ADSL2 implementation

Determining the cause of problems in ADSL service has at times been a challengingobstacle in ADSL deployments. To tackle the problem, ADSL2 transceivers have been

enhanced with extensive diagnostic capabilities. These diagnostic capabilities providetools for trouble resolution during and after installation, performance monitoring while inservice, and upgrade qualification.

First-generation ADSL transceivers operate in full-power mode day and night, evenwhen not in use. With an increasing number of deployed ADSL modems, a significantamount 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 maintainingADSL's "always-on" functionality for the user.

Another obstacle for ADSL deployment was the fact that telephone wires are bundledtogether 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 implementationby seamlessly adapting the data rate in real-time. This new innovation, called seamlessrate adaptation (SRA), enables the ADSL2 system to change the data rate of theconnection while in operation without any service interruption or bit errors. ADSL2 simplydetects changes in the channel conditions-for example, a local AM radio station turningoff its transmitter for the evening, and adapts the data rate to the new channel conditiontransparently to the user.

Data rates to homes and businesses can be significantly increased by bonding multiplephone lines together. To enable bonding, the ADSL2 standards support the ATMForum's inverse multiplexing for ATM (IMA) standard (af-phy-0086.001) developed for traditional ATM architectures. Through IMA, ADSL2 chipsets can bind two or morecopper 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 theADSL2 standards family as G.992.5. The ADSL2+ recommendation doubles thedownstream bandwidth, thereby increasing the downstream data rate on telephonelines shorter than about 5,000 feet.

While the first two members of the ADSL2 standards family specify a downstreamfrequency band up to 1.1 MHz and 552 kHz respectively, ADSL2+ specifies adownstream frequency up to 2.2 MHz (see Figure 2). The result is a significantincrease 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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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 useonly 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 thecentral office (CO) and a remote terminal (RT) are present in the same binder as theyapproach the end users location. The crosstalk from the ADSL services from theRT onto the lines from the CO can significantly impair data rates on the line from theCO. ADSL2+ can correct this problem by using frequencies below 1.1 MHz from thecentral office to the remote terminal, and frequencies between 1.1 MHz and 2.2 MHzfrom the remote terminal to the end users premise.


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

ADSL Standard Annexes

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 anddownstream transmission. Enclosed you will find a brief overview of the differentannexes:

ANNEX ENVIRONMENT ADSL ADSL2 ADSL2+A POTS YES YES YES

B ISDN YES YES YESC TCM-ISDN YES YES YESI (ADSL) TCM-ISDN YES YES YESI (ADSL2) POTS YES NO NOJ ISDN NO YES YESL (READSL2) POTS NO YES NOM (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 thelittle 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 officemarket. As download speeds have increased and more bandwidth has becomeavailable, small businesses and remote offices of larger organizations are starting to take

advantage of broadband and its ability to deliver streaming media, multi-media, andhigh-traffic business applications.

Even though both residential and business users are taking advantage of the sameaccess technology, their access device requirements are very different. So what arethe 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:

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 wiseto select an ADSL router that complies with all the main ADSL standards as describedbefore. In this case, you can migrate to the newer standards once they becomeavailable from your service provider without having to forklift-upgrade your existingequipment.

Security

One of the most important things to look out for when selecting an ADSL access devicefor business purposes, it its security capabilities. Communicating in the residentialenvironment does not necessarily require indepth security features. However, when wetalk 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 AreaNetwork (LAN) is part of the solution. As sensitive information is exchanged betweenremote and/or home offices and the headquarters, ADSL routers with integrated VPNcapabilities allow users to make a tunnel with a remote site directly to secure the datatransmission 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 thereforehaving management tools such as Telnet, CLI, FTP, Web GUI, and SNMPv3 at handare crucial. This holds true especially if you have no IT personnel at your remote officeor home office.


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Quality of Service

As download speeds have increased and more bandwidth has become available, smallbusinesses 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. As these applications compete for bandwidth, a business-class ADSLrouter should provide you with the capability to prioritize traffic based on the traffictype. This feature is called Quality of Service (QoS). The QoS capabilities give youfull control over which types of outgoing data traffic should be given priority by theADSL router, ensuring important data like customer information or managementinformation move through the router at lightning speed, even under heavy load. TheQoS 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 tonowadays popular Voice over IP (VoIP) systems, you should select a ADSL router thatenables you to leverage your existing analog phone equipment, but still use theInternet to make and receive phone calls.

ADSL routers can support cost-effective, toll-quality voice calls over the Internet byintegrating 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 additionintegrates an RJ-11 FXO port for inbound and outbound calls transmitted throughPSTN. 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+ Router TM and DL710 ADSL2+ Router TM

address all these special requirements described above. Both routers are designedspecifically for the small business and remote office market.


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Conclusion

Many carriers and Internet service providers are currently upgrading their networkinfrastructure to integrate ADSL2+ as their new broadband standard offering. Theincreased 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 therequirements of ADSL CPE devices dramatically as business have different featurerequirements than residential users. As a result, a new generation of all-in-one ADSLgateways will enter the market soon.

About Quick Eagle Networks

Quick Eagle Networks, Inc. is a provider of intelligent WAN access solutions for FrameRelay and IP networks, and the world leader in multilink access devices. The company'sproduct portfolio ranges from traditional CSU/DSUs, access multiplexers, multilinkaccess devices, bridges, WAN probes, to routers (NxT1/E1, ADSL, ADSL2, andADSL2+), providing expanded functionality for reduced cost at the LAN/WAN interface.Founded in 1985 and recognized worldwide for its Digital Link and Quick Eagle brandproducts, the company serves many of the world's leading enterprises and carriersincluding Boeing, Wells Fargo, Bank of America, Citigroup, EDS, MCI, Sprint, British

Telecom, Deutsche Telekom, and France Telecom. Quick Eagle Networks is an ISO9001:2000 certified company, with headquarters in Sunnyvale, California and sales anddistribution offices worldwide.

For more information about Quick Eagles full range of WAN access solutions visit our website at www.quickeagle.com or email [email protected].

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 containedherein is believed to be reliable but cannot be guaranteed to be complete or correct. Created 09/05 - Version 1.4

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