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It is appealing to think of obtaining all the elements of a DSL
solution from a single vendor, but that approach is at odds with major
trends in this market:
- PC manufacturers are starting to ship systems
with built-in G.lite modems, and buyers may expect you to support them.
- Some of the more interesting vendors only
provide the telco site equipment, and others only the CPE.
- Some product lines do not include the essen-tial
functions for aggregating DSL traffic at the central site, and making
it compatible with what the ISP can support on the uplink. Indeed, some
very successful new companies have made a business of satisfying just
this niche market.
These factors make interoperability and standards compliance
crucial considerations in ven-dor selection. That importance is a result
of the many technical standards involved in the use of DSL, including:
the versions of DSL modulation on the copper pair (QAM, CAP, DMT), multiplexing
on the DSL line (ATM, FUNI, TDM), framing on the derived channels (PPP,
frame relay, Ethernet) and some optional features such as Ethernet bridging
or IP routing, Network Address Translation (NAT) and Quality of Service
(QoS) tagging. There are also products from major vendors that are entirely
proprietary, and which will be very expensive to replace or convert
to achieve interoperability if it becomes a necessity.
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The industry appears to be converging on a small set of preferred
options, in the interest of interoperability, but it still would be easy
to get deeply committed to a DSL product line that will have a very limited
useful life. Proprietary products, those compliant with outdated standards
and those whose anticipation of the standards was wrong, might have to
be replaced to meet even currently-predictable needs. Even compliance
with the most widely accepted stan-dards leaves room for differences.
At least one vendor has told us that the final version of the G.lite standard
has elements that can only be satisfied with new hardware for their pre-standard
DSLAM line cards and CPE modems. Early adopters of those products face
a time-consuming and possibly expensive replacement of equipment in the
field in order to be capable of multi-vendor interoperability.
The wise buyer will look at the fine details of claims of compliance
with the standards the industry is adopting, will insist on credible proof
of interoperability claims at the product-number level (not just a list
of the other manufacturers) and will require a contract insuring cost-free
replacement or upgrading of products that fail to live up to the pre-sales
claims of the vendor.
Many telcos tend to purchase DSL equipment with
a "Purchase Order" buy-the-box approach, just as they would
with DLC equipment. Considering the evolving nature of this technology,
it is probably advisable to utilize a "systems" approach with
either performance-based specifications or a Request for Proposal. This
will provide some protection and shift the responsibility on the vendor/integrator.
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