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April 26, 1999

DSL Comes Together

continued...page 2 of 3

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As expected, though, these problems were solved by installing low- cost, low-pass filters on each phone in the house. DSL customer-premises equipment, correspondingly, is expected to come equipped with high-pass filters to avoid interfering with household voice traffic when data services are in use.

Other Alternatives
While vendors and customers await the rollout of UADSL, existing proprietary technologies that run over the same dry copper pairs, and offer similar price points along with typically splitterless deployment, are gaining a small foothold.

Paradyne's Multiple Virtual Lineoffers faster symmetric access than UADSL (typically 768 Kbps at 12,000 feet) and can reach farther (128 Kbps at 35,000 feet). The "virtual line" aspect of MVL refers to its ability to network up to four phone outlets at the customer premises with each line sharing the 768-Kbps bandwidth--a feature Paradyne no longer promotes. "Because of the emerging home-networking initiatives, we're not hyping the multiple-line drop aspect of the product," says Frank Wiener, VP of Paradyne.

Other technologies that generally require no "truck roll," a visit to the customer premises to split wires, include Cisco Systems' (formerly Netspeed's) EZ-DSL technology. It's an RADSL variant that uses Carrierless AM/PM (CAP) line modulation and can handle up to 1 Mbps symmetric or 1 Mbps upstream and 7 Mbps downstream asymmetric. Nortel Networks offers its 1-Meg Modem with a maximum throughput of 320 Kbps upstream and 1.3 Mbps downstream at a distance of 15,000 to 18,000 feet using Quadrature Amplitude Modulation.

While these proprietary technologies each offer minor advantages over UADSL, none will likely maintain any momentum after UADSL is launched, and it will be up to the vendors to supply UADSL ports to their DSL Access Multiplexor boxes in the central office to accommodate new customers.

HDSL2 Shines
UADSL and its competitive technologies will sometimes work for business users who require 350 Kbps or less of symmetric bandwidth, but for more serious applications that require higher speed and managed connections, such as E-commerce and high-quality video, other forms of DSL will be used.

As an inexpensive and flexible replacement for leased T1 lines, the HDSL2 standards are eagerly awaited by the DSL industry. HDSL2 replaces the aging HDSL standard that required two copper pairs. HDSL2 uses only one copper pair and is potentially rate adjustable.

"By using only one copper pair, competitive local exchange carriers have their costs cut in half. That can translate into major savings for MIS managers," says Richard Sekar, director of product marketing for Copper Mountain Networks Inc. HDSL2 uses OPDIS line coding, which maintains spectral compatibility at different line rates, giving HDSL2 the potential for multirate implementation. In contrast, HDSL uses 2B1Q line coding, which maintains spectral compatibility only at T1 speed.

Though not all end-to-end HDSL2 standards are finalized, vendors are slowly coming out with preliminary chipsets. HDSL2 will quickly be-come the main replacement for leased-line T1s and will be popular for corporate VPNs as well.

Value-Added Propositions
With the price of DSL poised to drop precipitously and the number of seats--both business connections and consumers--climbing, vendors are looking for ways to provide value-added services, and to break into even larger markets. One of the most obvious mass markets for DSL is the more than 100,000 multitenant office buildings--and even more numerous apartment buildings--in the United States.

These types of buildings are almost always wired with twisted copper pairs suitable for DSL. They can be efficiently and cheaply networked by putting a DSLAM in the basement and connecting back to the incumbent or competitive local exchange carrier using DSL or other technologies. More important, once the installation is complete, DSL can be used within the building without being deployed outside.