tomer's site to
install the splitter equipment, which increases the cost to the provider attempting to roll out DSL service.
The "lighter" version of DSL eliminates the need for a splitter by relying on signal-processing techniques to filter out interference. Another benefit: The light version of DSL could be implemented in a software-only solution on a Pentium-based or faster PC, or in a modem that end users can buy through normal retail channels. Dual-mode modems could even support DSL light and regular 33.3- or 56-Kbps analog connections. Such modems would get DSL service providers out of the business of supplying -- and supporting -- their end users' access equipment.
One caveat with these lighter DSL implementations is slower connections -- about 1 Mbps downstream to the customer, compared to about 6 Mbps with ADSL. But with more-capable digital signal processors (DSPs) or, in the case of a software-only implementation, faster CPUs, the speed of DSL light could improve. Even so, this versio
n of DSL is faster than analog modems and ISDN, and it provides an easy upward migration path to full-rate ADSL, provided that the customer's and central office's equipment are based on the same standard.
Another caveat is the question of standards. Aware and other companies base their line-encoding schemes on the discrete multitone (DMT) standard, but Rockwell says its CDSL scheme is based on a proprietary line-encoding standard.
In addition, vendors worry that if the International Telecommunications Union (ITU) group responsible for setting the new standard for this brand of DSL adopts something other than DMT, it will hinder acceptance. "If the ITU chooses something that's not DMT, that could result in years of work getting delayed," says Greg Whelan, director of business development at Aware. If this new DSL is based on DMT, that would provide an easy migration path to faster DSL speeds, DMT proponents say.
Whelan comments that adding the proper equipment for DSL at each central-office
site is a big enough commitment for telephone companies and that it's unlikely the phone companies would want to support two standards: DMT and something else. (Rockwell officials say that although their initial proposal to the ITU is not based on DMT, they will adopt whatever the standard is; DMT proponents will lobby to ensure that a DSL-light standard is based on DMT).
When such modems will appear is currently unclear. Rockwell and Toronto-based Northern Telecom recently announced that they will offer a CDSL modem for about $200 in the second half of this year, but other vendors, such as Aware, could offer them sooner.
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A future version of DSL, without the splitter, could be easier to roll out to end users.
DSL Gets Consumer-Friendly
