Monday, 2 March 1998
By Mitch Gitman

If U S West won’t let you get its DSL MegaBit Services when they come out this spring, don’t take it personally.

The limits to who gets DSL, and how much, come down to limitations inherent to DSL technology itself, limitations that aren’t corrected by sticking a DSL modem bank in a local phone company office or by fixing some old copper wire out in the field.

In trying to explain the roadblocks to DSL’s deployment, it’s easy to blame the copper it runs over.

After all, twisted pair copper is an old-fashioned, analog technology dating back a hundred years. Over the past 15-20 years phone companies have been assiduously replacing the copper between central offices (COs) with digital, high-capacity fiber optics, where beams of light are shot through super-thin glass pipes.

Indeed, from its invention in 1989, DSL has always been seen as a way to send broadband communications in spite of copper’s incapacity.

But in fact, one critical barrier DSL faces in Tucson, and in Phoenix as well, is of an opposite nature. You could almost say there’s not enough copper.

U S West MegaBit exec Greg Gum maintains that 60 percent of phone lines in Phoenix are able to carry the DSL which U S West introduced in Phoenix a week ago to replace its original DSL offering.

For at least three-quarters of the 40 percent of Phoenix customers who currently can’t get DSL, Gum said, the issue is digital loop carriers (DLCs). A DLC is a digital line (usually fiber) that runs out from the CO into the local copper network, replacing existing twisted pair. The problem is, DSL doesn’t work over DLCs.

The solution would be to install DSL modem banks, called DSLAMs, in the small boxes where the fiber of the DLC ends and the copper begins, analyst Michael Finneran said. Such a “mini-DSLAM” has not been invented yet, Finneran said, but considering the current breakneck pace of data communications development, he figures something should be on the market within a year.

That still leaves the other key problem preventing DSL adoption in Tucson. Paradoxically, it is one of too much copper.

The whole trick to DSL is that it sends information over super-high frequencies, much higher than voice’s bandwidth, explained Finneran, who wrote an article about the difficulties DSL faces in the January issue of Business Communications Review. The higher a signal’s frequency, the more data can be squeezed into it. But the higher the frequency, the shorter the distance a signal can effectively travel over a carrier like copper.

The DSL U S West is using can only run to a distance of 18,000 feet (3.4 miles), relatively far as DSL distances go. And that’s 18,000 wire feet, not feet as the crow flies, Puffett pointed out. Even within that 18,000-foot range, the farther away you are from the CO, the lower the DSL speeds you should qualify for.

In a place as spread out as Tucson, that presents a major problem, said Matthew Grossman, network operations project leader for StarNet, the Internet service of The Arizona Daily Star. For example, Grossman lives six miles from his CO, and that’s in what hardly could be called a remote part of town.

Ironically, perhaps the most sensible solution to the distance problem ultimately poses the other problem, Grossman said – digital loop carriers.

Impairments in the copper itself, according to U S West, are a relatively small concern, and in some cases they’re fixable.
Qualifying for DSL
In April or May, when MegaBit Services is introduced in Tucson, customers will be able to call a toll-free numbers to find out if their phone numbers support DSL and if so, order the service.

On a test call for a number in Scottsdale, a U S West representative said it would take about 10 days to get the service turned on and recommended professional installation of the modem and Ethernet card.

US West will offer MegaBit Services at the following Tucson central offices: Catalina, Cortaro, Craycroft, Flowing Wells, Rincon, Tanque Verde, Tucson East, Tucson Main, Tucson North, Tucson South.

US West officials declined to say which exchanges (three-digit prefixes) those COs serve. However, on a test call to US West customer service, Star Tech was told which CO served a particular Tucson number.