The 1.5-Mbps/384-Kbps speed limitation may seem restrictive compared with DSL's typically advertised maximum downstream speed of 7 Mbps, but it is a rational limitation based on empirical testing of typical customer wiring scenarios and on the current overall bandwidth available through ISPs.

The Tools for DSL Deployment DSL lines require quality copper loops--that means no load coils, no more than 2,500 feet between bridge taps and generally a (driving) distance of 18,000 feet or less from the CO (central office). At higher speeds, distance requirements become more critical and lines are more easily disrupted by "disturbers," such as ISDN and T1 lines in the same wire bundles as the DSL lines.

Although G.lite is being promoted as a "splitterless" standard, the engineering realities of new standards and new silicon, coupled with the wide variety of possible installation scenarios, mean that, initially, there likely will still be some need for splitters, filters and, in some cases, even new customer-premises wiring. As the G.lite standard matures with a better understanding of the issues, as well as better vendor chip implementations, it probably will become closer to being truly splitterless.

Of course, even at G.lite speeds, the UARTs (Universal Asynchronous Receiver/Transmitters) on conventional PC serial ports will be unable to keep up. Thus, external, single-user PC modems that utilize serial technology will use USB (Universal Serial Bus) ports on PCs or possibly enhanced parallel ports.

Router and bridge units, the only DSL modems currently available, use Ethernet. Newer chipsets coming to market, such as Rockwell's recently announced V.90/ADSL combo chipset, combine the G.lite and V.90 standards in one modem, offering customers a choice of connection profiles.

Available bandwidth for Internet access is another consideration. When Bellcore first published its DSL work in 1989, the intention was to use DSL for video-on-demand services, not pure data traffic.

Few service providers could handle 1,000 users with 7-Mbps DSL links to the Internet. G.lite's 1.5-Mbps/384-Kbps limit is a reasonable maximum, and, in any case, it's likely that many customers will opt for slower symmetric speeds to handle applications like high-quality, point-to-point videoconferencing, which generally requires 384-Kbps symmetric bandwidth.

What to Buy and When to Buy It For IT buyers, it's a confusing time. Despite frequent press releases touting rollouts of DSL access, corporate mergers and equipment deals, the fact is that DSL availability is still sparse and there is almost no interoperability among equipment.

Further, at least nine varieties of DSL are available (see "Key DSL Variants"), many using incompatible modulation schemes, such as QAM, CAP, DMT and 2B1Q. Many vendors are using proprietary DSL chipsets, further complicating the issue. So, IT buyers right now are faced with single-vendor solutions.

In addition, because the DSLAMs (DSL access multiplexers) that are connecting corporate users are selected and owned by ISPs, CLECs and ILECs, corporate IT buyers must accept the carrier's vendor choice. Only a very large IT account might be able to influence a provider's choice of DSL equipment.

Does this single-vendor state of affairs and grab bag of DSL implementations matter? The answer is both yes and no. Ultimately, any particular end-to-end solution is simply another card in a DSLAM box and a corresponding CPE unit. When the G.lite standard arrives, it too will be another card that slides into the DSLAM with a corresponding CPE unit. Therefore, the penalty for customers buying into DSL today may only be the eventual replacement of nonstandard CPE and, if the company owns the DSLAM, upgrading some of its rack-mount cards.

Because DSL technology is evolving quickly, with new hardware revisions that are more noise-tolerant and can traverse longer distances, these upgrades likely would be necessary even if the standard were not available within a year's time. If your company can wait until the second quarter of 1999, that may be the best time to consider deploying a DSL technology. By then, G.lite equipment should be widely available and more nationwide sites should have DSL lines available.