An In-Building DSL Approach To
Voice Over Broadband In Multi-Tenant Units
BY DAVID KAMM
Those familiar with Digital Subscriber Line (DSL) technology may also recognize the term "in-building
DSL," meaning the deployment of DSL inside a building using
in-building copper pairs, versus using DSL as the last-mile technology
connecting a building to a service provider. In-building DSL is an
appropriate and useful technology for hundreds of thousands of commercial
multi-tenant units (MTUs) in the U.S. and other regions of the world,
especially where these buildings (and their tenants) can not be reached
with local-loop DSL services.
Another term you're likely familiar with is Voice over Broadband (VoB),
which encompasses a number of methods for
delivering packet telephony services over high-speed access
connections. Voice over DSL (VoDSL) is a specific example of VoB, and it is
gaining widespread acceptance as a viable, cost-effective approach for
delivering multiple voice lines, as well as high-speed data services, over
a single twisted copper pair. According to TeleChoice, more than
20 service providers had announced commercial VoDSL services in the
U.S. and Canada as of Q2 2000. Deployments of VoDSL are expected to ramp
up dramatically as new providers conclude field trials and begin
to aggressively market bundled voice and data services to end users. Key
markets for VoDSL (and VoB in general) include millions of small to
midsize businesses (SMBs) as well as residential users with multiple phone
lines and computers in the home or home office.
Adding Voice To A DSL Network
Adding packet voice to a previously data-only DSL network places
new demands on the access network and the in-building equipment. Whereas
data-only services can generally get by with best effort Quality of Service (QoS) characteristics, packet voice services must have
low, predictable delay (latency) in order to ensure toll-quality voice.
Another factor -- amplified by the clustered nature of MTU-based
subscribers -- is that not all MTUs can get DSL services today. Many
commercial buildings are simply too far from a DSL-capable Central Office
(CO) to receive services. In addition to the distance-related limitations of
DSL, many relatively new (less than 10 years old) commercial
properties are served off of Remote Terminals (RTs), rather than directly
from a central office. This adds to the DSL availability problem. Many RT-served
buildings are actually close to a CO, but nevertheless are locked out of
DSL service unless an RT-based or in-building DSL solution is available to
them.
The problem of DSL availability in the local loop is greatly
exacerbated once we start thinking about very high speed, shorter-reach
DSL variants like VDSL. In fact, depending on the density of MTUs around
any given central office, the number of buildings that fall outside the
DSL service range can grow exponentially as the service radius is reduced
from SDSL range to VDSL range. Unfortunately, this means the resultant
lost revenue opportunity for ICPs grows exponentially as well.
An in-building DSL approach can bypass this problem completely. Even a
"long" in-building copper loop is unlikely to exceed 1,000 feet
or so, making in-building VDSL speeds up to about 50 Mbps a reality. Of course,
the DSL Customer Premise Equipment (CPE) must be equipped with VDSL interfaces, and the in-building DSL
concentrator must have the architecture and processing power to handle
multiple VDSL feeds at full line rate.
Data-Only Services Aren't Enough
Many Integrated Communications Providers (ICPs) and most industry
analysts have come to the conclusion that data-only services in the MTU
are not enough to generate long-term profitability and subscriber loyalty. A
data-only approach also makes it harder to recover initial investments and
recurring costs, since it requires more subscribers for the ICP to reach a
break-even point. The overwhelming revenue opportunity for MTU-focused
ICPs and an attractive path to profitability with broadband access is to
offer packet voice services in addition to data services -- true
multi-service access for tenants. VoDSL is expected to be a highly
profitable service offering for ICPs, with excellent return on investment
and net present value characteristics over a wide range of pricing
structures. Similarly, end users stand to benefit from reduced bundled pricing, a single point of customer
contact, and simplified billing.
For this article, let's concentrate on delivering VoB services to MTUs via
in-building DSL where DSL as a local loop option isn't available. Some analyses
indicate that when both fixed and monthly recurring costs are factored in,
in-building concentration can be more cost effective than wiring
each business/subscriber directly back to a CO-based DSLAM. This is due in
part to the fact that with in-building concentration, fewer uplinks are
needed and oversubscription is an option. Service providers can also
leverage an in-building concentration strategy to avoid the recurring
delays associated with provisioning individual subscriber lines from
another telco, saving time and money. By utilizing a platform called an Integrated Concentration
Device (ICD), the ICP has the option of wiring
phones, key systems and PBXs directly to the ICD in the basement or wiring
center, avoiding the purchase of dedicated IADs for each subscriber.
New Options For Deploying MTU-Based VoDSL
An ICD configuration (depicted below) is a new alternative for MTU-based VoDSL.
It integrates
subscriber voice CPE such as phones and key systems directly into the
concentration platform, allowing the ICP greater freedom to offer
different subscriber services with one platform.

This approach recognizes and leverages the fact that the MTU-based
subscribers are co-located with each other, which provides much greater
deployment flexibility.
Conclusions
The opportunity for packet voice services in MTUs is great, and the
revenue potential very large, especially when compared to a data-only MTU
services strategy. Service providers have a number of choices for
delivering VoDSL in MTU environments, including a new approach that
incorporates both DSL and voice customer premise equipment in a single
concentrator.
An in-building DSL strategy can be an excellent alternative to local
loop DSL, even where subscribers are close enough to be served from
CO-based DSLAMs. In-building DSL solves the well-known distance
and reach problems associated with VoDSL, and is attractive for many more
reasons as well.
Adding DSL-based packet voice services in MTUs presents the
first real QoS test for in-building DSL concentrators. Concentration
products designed primarily for MTU-based data services will be the
weakest link in the multi-service access chain. Only platforms based on
true multi-service architectures will succeed as the foundations for
toll-quality voice, broadcast-quality video, and other QoS-intensive,
highly profitable services in the MTU.
David Kamm is the
director of marketing for Avail
Networks, Inc. Avail Networks designs, develops, and markets network
access solutions worldwide for next-generation convergence applications
such as integrated data, voice, and video over single broadband
connections. Avail's flagship products -- the Frontera family of
multi-service access platforms -- enable service providers to deliver
integrated broadband communications services to end-user sites in
commercial office buildings, office parks, and single-business locations.
For additional information on standards-based voice over broadband
topics, visit www.openvob.org.
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