Tài liệu HDSL2 : INTEROPERBILITY AND BEYOND ppt

HDSL2:
I
NTEROPERABILITY

AND
B
EYOND
Introduction
In order to function, services transported over traditional HDSL require transceiv-
ers at both ends — central office and customer premises — provided by a single
vendor. Standards currently being considered for its replacement, HDSL2, would
allow transceivers from different vendors to interoperate. The obvious benefit for
purchasers of such devices is the freedom to “mix and match” components from
different manufacturers, increasing competition and ultimately reducing costs.
But the real, long-term benefits of interoperability are less apparent and far more
important.
Interoperability implies standardization. With interface standards in the public
domain, the functions of remote HDSL2 equipment will eventually be built into a
variety of devices, such as PBX and DSU equipment. This plug-and-play compat-
ibility with HDSL2 will drive an explosion in the demand for HDSL2-based prod-
ucts and provide a huge increase in the potential market for the services it sup-
ports. It is therefore in service providers’ interest to make interoperability a
requirement in any HDSL2 equipment they acquire.
Standardization may suggest that the product is becoming a commodity but, in
the case of HDSL2, nothing could be farther from the truth. The basic functions
needed for interoperability may be the same, but beyond that basic level, HDSL2
equipment will be highly differentiated. The differences will affect cost, installation,
reliability and support and determine long-term profitability. For most providers,
HDSL2 will be part of an array of services, and a step toward new ones they will
provide in the future. Today’s choices will largely determine how well HDSL2 fits
your product mix today and migration path tomorrow.

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HDSL2: Interoperability and Beyond
Traditional HDSL is a robust transmission scheme specified in a working report gener-
ated by ANSI. That document, however, left too much leeway in product design for
equipment from various manufacturers to interoperate. In other words, each vendor’s
products are proprietary, working only with corresponding devices from the same
vendor. At the time, this was not a critical issue for HDSL equipment buyers, for a
number of reasons:
• There were only a handful of vendors providing HDSL
• As a digital T1 service that could be delivered over existing copper to a hungry
market, HDSL was so profitable that equipment cost was almost irrelevant
• Once vendors acquired large accounts, they had valuable “turf” to protect from
competitors, so there was little interest in creating a standard
• Buyers with large investments in HDSL equipment had little motivation to
embrace a new interface that would render their existing equipment obsolete
Times have changed. The demand for digital services has skyrocketed. Small branch
offices and even home offices now use the kind of bandwidth once reserved for large
corporations. There are even larger markets waiting to be served but, like most mass
markets, they are more price-sensitive.
At the same time, growing demand is driving changes in the supply side of the market.
Unbundling has opened the door to new competitors. The variety of DSL transmission
schemes is growing, as is the number of equipment vendors. Time frames are shrinking
and the business environment for service providers is more competitive and complex
than ever.
Service providers can no longer be assured of profit by simply offering a service based on
any convenient DSL service. As the market becomes more competitive, short-term,
tactical planning can lead to expensive mistakes and technological dead ends. What is
needed is strategic planning that addresses the broad range of issues affecting the
market. These include:

• Market segmentation
More users mean more applications, from mission critical business to casual residen-
tial use. Successful service providers will target specific sub-markets rather than
trying a “one-size-fits-all” approach.
• Limited availability of copper pairs
Just a few years ago, copper was readily available as a medium for digital services.
Today, the growth in demand requires that copper be conserved.
• Increased vendor participation in the DSL market
More vendors are entering the DSL market. Some will conform to standards, while
others offer proprietary products. Service providers will have to carefully examine the
future implications of today’s vendor choices.
• Shrinking time-frames
As competition increases, service providers will have less time for deliberation. The
needs they don’t meet today will be met by competitors tomorrow.
• Increasing variety of services
Until now, digital services meant T1. That will not be true in the future. No one can
predict with any accuracy the demands that service providers will face.
• Decreased separation between user facilities and the network
The network interface will begin to migrate into user devices. This has happened in
many technologies in the past, e.g., “cable ready” television. While it may initially
deprive service providers of a small source of revenue, but it will be a major driver of
the growth in demand for service.
Background
The Changing
Market
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HDSL2: Interoperability and Beyond
It may not be apparent in the flood of information regarding DSL, but leaders in the
industry are taking some very concrete steps toward addressing these issues.

The segmenting market has given rise to a split in DSL approaches. The two major
segments are HDSL2 and ADSL. ADSL, an asymmetrical, adaptable-rate service, is
aimed squarely at the residential market. HDSL2, a more robust, symmetrical service is
designed for the critical, two-way requirements of business applications. While the ADSL
market promises to be large, HDSL2 has the greater revenue potential per line. This is
due to the mission-critical nature of the applications.
HDSL2 also addresses the problem of shrinking copper stock, literally doubling the
carrying capacity of each copper pair. As demand drives up the value of copper, HDSL2
will, in some cases, replace existing HDSL. The minor inconvenience of having to
replace existing HDSL equipment will be more than offset by the increased revenue
potential of HDSL2.
While the number of vendors will grow, buyers can simplify their decisions (at least in
the HDSL2 market) by focusing on vendors offering interoperable systems.
Interoperable HDSL2 will let carriers standardize their operations without limiting
future choices, and seek competitive prices without affecting ongoing operations. And,
should a vendor leave the market or fail to provide adequate service, the carrier will be
free to find alternative sources of supply. Most important, however is the open interface
that interoperability provides.
The most familiar example of interoperability is the common wall plug, the access point
for 60 Hz. “house current.” It supplies electricity to your laptop computer or your hair
dryer equally well. You can plug the same device into a socket in Seattle or Sarasota,
with identical results. If you build a house, you can buy your outlets from any vendor,
knowing that they will handle any utility company’s current and any 110V appliance you
care to use. This standardization, which we generally take for granted, makes possible
the electric tools and appliances we use everyday.
For years, telecommunications did not require the same degree of standardization. Until
relatively recently, at least in the U. S., a single entity provided virtually all equipment
and service. After 10 years of litigation, the Carterphone decision — Carterphone was a
simple acoustic coupler that connected a two-way radio to a telephone — opened the
network to outside devices. But it wasn’t until the early 1980s that divestiture opened

the door to large-scale deployment of what the phone company called “foreign” equip-
ment.
But, even as AT&T separated into RBOCs, habits changed slowly.
In the 1980s, the standard RJ-11 telephone jack replaced the hard-wired telephone
connection, but users were still being urged to notify the telephone company before
plugging in their answering machines. Those answering machines were the first real
answer to the question, “whatever would you want to connect to the phone network
besides a telephone?”
Today, it sometimes seems that everything but the blender is connected to the network.
Cell phones, computers, alarm systems and gas meters all take or make calls. You might
not call a kitchen appliance to “check on a cake in the oven,” but it doesn’t sound like
science fiction either. The simple fact is that, like those who designed the standard
Strategies for
Growth
The "Plug-
compatible"
World
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electrical outlet, network service providers have no idea what their services may
be used for in the near future.
Since its inception, HDSL has been a niche technology used for providing T1
service. It was an easy, inexpensive way for phone companies to provide band-
width, and users didn’t care how they did it or how much it cost. Service provid-
ers owned or leased the copper and provided the termination equipment at both
ends, so there were no issues of interoperability.
It is tempting to view HDSL2 as a simple replacement for HDSL, providing the
same service over one copper pair instead of two. But that would overlook the
real future of digital service. As an interoperable service, HDSL2 has the poten-

tial to open whole new avenues of growth.
As the number and complexity of applications grows, more and more users are
finding 56 kbps modem access inadequate. As more employees telecommute and
small office/home office applications grow, the distinction between business and
residential users is blurring, but one thing they are finding in common is a need
for LAN extension. Business users want the same kind of server access in their
homes or branch offices that they had at headquarters. Video, once a futuristic
fantasy, is promising to becoming commonplace. And gamers, once content
with what was available on a single machine, are now meeting others to play, in
larger groups, in real time and across unlimited distances. In other words, what
was once a voice-only — more recently voice and modem — network, has the
potential to become the unified medium for all the world’s data. The backbone is
already in place. What remains to be done is to open the last mile and create a
common “wall plug.”
Today, an international traveler carrying electrical appliances has to bring
adapters in order to use local electric power. Imagine the same situation existing
within a city or even a neighborhood. Without interoperability, this is exactly
what would happen as DSL migrates into network elements like digital loop
carriers (DLCs), add-drop multiplexers (ADMs) and channel banks. Each device
would need converters, depending on the specific vendor providing the digital
service. Obviously, this would hardly be conducive to “explosive growth,” either
for the equipment manufacturers or for service providers. Interoperable HDSL2,
on the other hand, will enable a new generation of high-speed modems, sub-rate
data services and symmetric Internet links.
Making the technology interoperable is not difficult. If anything it is more a
matter of will than of ability. Critical issues include:
• Standardized message sets (tip/ring reversals, loopback activation, loop
margins, HDSL2 LOSW and DS1 LOS)
• Performance monitoring messages (AIS-CI, RAI-CI and NPRM)
• Line coding

• Forward error correction
• Spectral density
A number of vendors have already committed to HDSL2 interoperability and the
ANSI T1E1.4 committee is working on the issues.
For network builders and service providers, interoperability is an important
criterion for HDSL2, but not the only one. But HDSL2 will not operate in a
vacuum, so equipment decisions should take into account both the larger
Beyond T1
Creating
Interoperability
The Bigger
Picture
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HDSL2: Interoperability and Beyond
communication environment and future needs. From the very start, HDSL2 may be
delivered alongside other services like ISDN, Frame Relay, PCS and ATM. As a copper-
based product, it may or may not coexist with fiber-based services. And, over time, it will
almost certainly be superceded by newer copper- or fiber-based services.
Communications services, already more competitive than they have ever been, are
changing at an astounding rate. Today’s highly profitable service may be tomorrow’s
commodity, with razor-thin margins. As technologies change, services compete not just
with other similar services, but with completely different ones. Cable TV is challenged by
direct satellite broadcast; wired telephony faces off against wireless.
The exploding demand for service may make the market look easy, profitable and
thoroughly appealing but, in order to survive, service providers have to look down the
road. Initial costs are obvious, but what about the less apparent costs of installation,
turn-up and troubleshooting? High maintenance costs may not be a problem when
margins are large, but those ongoing costs can be brutal when competition puts the
squeeze on margins. This is where the “commodity myth” — the mistaken belief that all

systems are alike — can set the unwary service provider up for failure.
Interoperability does not eliminate the need to compare features. It is a feature, but just
one of many that should guide your choice of HDSL2 systems. Collectively, the features
of your HDSL2 system will affect your ability to:
• Make money by expanding your market and increasing the value of your services
• Save money by reducing cost, simplifying installation and maintenance, and
eliminating unnecessary labor
• Make life easier by reducing downtime, increasing your span of control and simplify-
ing migration to future service offerings
HDSL2-based services may look like a commodity to users, but for service providers,
differentiation will be the key to success. Devices may interoperate, but competition
among equipment manufacturers will simply move to a higher level; the platform
within which HDSL2 functions. Platforms like ADC’s Soneplex
®
system will provide an
array of value-added capabilities far beyond simple service delivery.
These capabilities will ease installation and simplified maintenance. They will allow
remote management and diagnostics, and integration with other services. They may
provide increased densities to meet the market’s growing needs within the confines of
existing facilities. And they will provide forward compatibility. In short, HDSL2
interoperability will be just another feature within a larger approach to providing
multiple, targeted services to meet the yet-undefined needs of an unpredictable and fast-
changing market.
The right platform will help you make money by:
• Providing a wider range of services on a single platform, allowing you to better meet
customers’ specific needs
• Allowing you to expand systems as they are needed to conserve capital
• Letting you install and turn-up facilities faster
• Keeping facilities up and running, and earning revenue, using centralized preventive
maintenance and troubleshooting

• Letting you provide guaranteed service levels to those willing to pay for premium
service
Beyond
Interopera-
bility
4028 2/99 Original © 1999 ADC Telecommunications, Inc. All Rights Reserved An Equal Opportunity Employer
Specifications published here are current as of the date of publication of this document. Because we are continuously improving our products,
ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our
headquarters office in Minneapolis. ADC Telecommunications, Inc. views its patent portfolio as an important corporate asset and vigorously
enforces its patents. Products or features contained herein may be covered by one or more U.S. or foreign patents.
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HDSL2: Interoperability and Beyond
It will save you money by:
• Integrating multiple services on a single platform to reduce equipment cost
• Integrating components which might otherwise have to be purchased separately
• Providing maximum density to make best use of expensive central office real estate

• Integrating centralized troubleshooting and sectionalization, reducing maintenance
cost and eliminating the cost of an overlay network
• Allowing remote provisioning to eliminate or reduce turn-up cost
• Integrating your service platform with other systems with local and remote OAM&P
support
• Supporting proactive maintenance with ongoing performance monitoring
Finally, the right platform will make your life easier by:
• Providing a clear migration path to future service offerings
• Giving you the flexibility to change with market demands, competitive pressures and
changing technology
• Letting you expand or reconfigure the system without incurring unnecessary cost or
requiring “forklift upgrades.”
Despite the obvious advantages of interoperability for service providers, there will almost
certainly be HDSL2 equipment providers offering non-interoperable equipment. Such
equipment may cost less than equipment that meets the interoperability standard, but
the real cost will be paid in the future. Not only will service providers that purchase such
equipment find their future vendor choices limited, but also, their customers will face
limits on what, and how, they can connect to the network.
As important as it is however, interoperability is just the beginning. “Standardized”
HDSL2 equipment will be judged, not only on the equipment itself, but also on the
platform within which it functions. In order to win in today’s competitive markets, you
need every possible advantage. Interoperability will get you into the race, but integration
will help you win.
The Bottom Line