The White Paper Series

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

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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 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. 2

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

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provider’s central office to the customer site than upstream from the user to the central 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

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a POTS (Plain Old Telephone Service) or an ISDN channel. 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,

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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 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

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connection while in operation without any service interruption or bit errors. ADSL2 simply 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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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. 7

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

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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 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?

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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, businessclass 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 highend 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

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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. 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 lifeline 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. 10

Conclusion Many carriers and Internet service providers are currently upgrading their network

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infrastructure to integrate ADSL2+ as their new broadband standard offering. The 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 [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 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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