DSL in the real world

Sometimes technology that looks hot in the lab fizzles out in the real world. That’s why we tested one of the promising new digital subscriber line (DSL) products, Paradyne’s Hotwire Multiple Virtual Lines (MVL) modem, under controlled conditions (see story, page 60) and in our own offices.

For our trial under normal work conditions, we hooked up with HarvardNet, an early DSL provider that deployed its first DSL installation in early 1996. We used Paradyne’s Hotwire MVL modems and worked closely with Paradyne, which itself works closely with HarvardNet. Bell Atlantic provided the service, installed our jacks and connected our office to HarvardNet’s point of presence (POP).

Paradyne’s MVL is a proprietary implementation that doesn’t comply with underlying DSL standards such as Carrierless Amplitude Phase and Discrete Multi-tone. Instead, it uses something called Quadrature Amplitude Modulation, a method of encoding bits borrowed from high-speed analog modems. As a result, it’s not compatible with G.lite splitterless equipment and interoperates only with other Paradyne equipment on a service provider’s premises. Though this is a drawback, standards in this market have not settled down, and universal interoperability is not as critical as finding technology that works. Additionally, by not complying with standards, Paradyne was able to add to its product features that are incompatible with the standards, including support for as many as four drops off the same trunk line.

An advantage of the latest generation of DSL technology in general, and MVL in particular, is that it’s splitterless. This feature means you don’t need an additional device to separate the low-frequency voice traffic on your line from the higher frequency DSL data traffic. You just plug the DSL modem into the wall as you do your current analog modem. Besides a line and phone socket, a DSL modem has an additional socket that you must use to connect to the network interface card of a computer.

The Hotwire MVL modem is designed to plug directly into your existing phone jack and share your current line. Because our office phone system runs through a digital PBX, we had Bell Atlantic install a new line, and the company provisioned it for data only, so we weren’t able to test using a phone over the same line that was concurrently supporting data downloads. However, we did hook up our Hotwire MVL using a common phone extension cable and saw no evidence of performance degradation due to electrical interference or poor-quality cables.

Somewhat to our surprise, we liked DSL just fine. The speed of our dedicated hookup – rated at 768K bit/sec combined upstream and downstream – seemed just as fast as the shared T-1 we access over the corporate LAN. We were able to put two computers with different IP addresses (on the same subnet) on two jacks connected to the same incoming line, just as you have multiple phone jacks in your house. The computers were able to communicate over the DSL loop, which connected our Network World offices with a Bell Atlantic central office (CO) 1.8 miles away and a HarvardNet POP about 500 feet from the CO.

As with ISDN service, the most exasperating part of the DSL experience is dealing with the phone company and the service provider to get the configuration right. Fortunately in our case, both equipment and service providers were highly responsive. Nevertheless, it took 26 days from the time we first spoke with HarvardNet to the time we had lines installed and modems that could communicate over them, thanks largely to goofs by Bell Atlantic. The carrier canceled our entire installation order when we only wanted to cancel three of the four original lines they were to install.

Is this technology cost-effective? That depends on the available alternatives. In areas where service is available, cable modems will give DSL strong competition. Our MediaOne cable service, which provides shared 1.5M bit/sec throughput downstream and 384K bit/sec upstream, has nearly as good a response time, and at $50 per month, competes closely with HarvardNet’s $59 for 768K bit/sec DSL service or $49 for 384K bit/sec service. (The monthly subscription rate includes use of the MVL modem.) Service areas where IP over DSL and cable are available will likely have the lowest rates.

Cable providers have had 20 years to recoup the cost of building infrastructure and have a cash cow in their TV services to subsidize the Internet side of the business. However, they still have to send out a service representative when they install a cable modem. DSL promises an easier install, but its providers are still building their infrastructure and must dedicate some time and expense to evangelizing the technology.

Both technologies have great potential. Watching the market mature ought to be interesting.