At today's price points--which set DSL access and equipment at easily a factor of five less than comparable technologies, such as T1, and at least that much faster than ISDN at a similar price point--some companies are willing to buy DSL equipment now even if it means having to migrate to standards-based DSL later.

Jim Southworth, director of advanced network services and technologies for Concentric Network Corp., one of the larger ISPs focusing considerable resources on DSL, sees the forthcoming G.lite standard as the basis for a vast amount of future DSL deployment. He cautions, though, that customers buying in today will likely have to purchase new equipment within two years.

The TI Competition But despite DSL's radically less expensive equipment and service, Southworth says he doesn't see any of the DSL iterations supplanting T1 lines anytime soon. If anything, he says, he sees DSL driving T1 sales. The reason is manageability. T1 connections have been a staple of corporate America for years now and are comparatively easy to manage, with 24x7 monitoring, a wide array of routing options and guaranteed response time.

Also, unlike DSL lines, which have distance limitations of typically 18,000 feet from the CO, T1 line distances can be extended much farther from the CO using repeaters--roughly up to 50 miles in the local loop and much farther for long-haul T1 connections.

Although T1 services may not disappear in the short term, ultimately they will be used only for access. If you are close enough to the CO, DSL is the way to go, especially if you trust real-time services (voice/video) over packet networks.

The CLEC Playing Field Today's single-vendor source market for DSL hardware might make some customers wary of buying in, but it isn't stopping CLECs from aggressively pursuing collocation at COs around the country and deploying single-vendor solutions. Customers will have to purchase, at a minimum, the same vendor-specific CPE that the carrier is using. Later, when G.lite does come around and G.lite cards for the DSLAM equipment are available, existing customers are likely to stick with the same equipment vendors because of familiarity.

Because some DSLAM vendors already support multiple varieties of DSL in the same box, the move to G.lite is expected to simply require another variety of DSL card that slides into the rack. Thus, existing CPE will remain and new installations can proceed with G.lite.

Additionally, some CLECs are already deploying multiple DSL technologies for different purposes. Covad Communications Co., a DSL CLEC that is collocating its DSLAMs in COs around the country and selling its DSL service through various ISPs, uses RADSL (Rate Adaptive DSL) equipment from Diamond Lane Communications for its DSL service and IDSL (ISDN DSL) equipment from Cisco Systems for customers who aren't close enough to the CO or who want to change their existing ISDN equipment to DSL.

IDSL, which uses ISDN's 2B1Q line encoding and runs over existing ISDN copper that has been rerouted at the CO from the switched voice network, can be extended using repeaters as far as 30,000 feet from the CO. The downside is that it is limited to 144-Kbps symmetric speed.

Also, IDSL customers lose their ISDN voice services. But in some markets where ISDN lines are metered, including California, IDSL lines are attractive to customers because they are not metered and are deployed as "always-on" connections as opposed to dial-up links.

Covad deploys both IDSL and RADSL in order to reach as many customers as possible in any given region, according to company officials. However, that means deploying at least two DSLAMs, one from Cisco and one from Diamond Lane, in every CO. With CO collocation space at a premium and each DSLAM box requiring its own expensive back-haul circuit, the fewer DSLAMs required, the better.

And while no one is making money with DSL technology yet, Covad says it expects that to change. "The economics of this business are the best of any business I've ever been in," says Rex Cardinale, vice president of engineering for Covad. "When you look at the take rate [the number of customers in a region that subscribe to the service] that we have to get in order to be profitable, it's really small."