Spurred by relentless competition, the telephone companies are anxious to sign up as many customers as they can. Virtually every major telephone company in Europe, the United States, Canada, and throughout Asia- Pacific has announced commercial DSL rollouts.

According to technology market analysts International Data Corporation (IDC) in its report published on February 9, 2001, “The number of digital subscriber line (DSL) subscribers around the world will soar to 64 million in 2004.”

This wide availability means that many users who want to get DSL service can get it from more than one supplier. They can choose to take service from their telephone company and often directly from their ISP or even work with multiple ISPs that best meet their needs.

Telco DSL has a security advantage over cable or fixed wireless in that it uses a private, point-to-point connection to the telephone company central office. Nearby customers do not share the line so they have no access to other user’s data. It also means no shared bandwidth constrictions.

The telephone company’s digital subscriber service uses a signal impressed on your telephone, sometimes referred to as a POTS line. In principle, it works like the old telephone modems, but phone modem throughput was limited because it used the audio frequency range (500 to 2,500 Hz), which the human ear can detect and the phone system was originally designed to carry.

By raising the frequency of the carrier tone far above the range of human hearing (4,000 Hz), the phone company engineers found that they could make it carry much more data and do so without interfering with the lower frequencies that we listen to.

The scheme also gave the added benefit that people could continue to use the phone as they always had—for talking—at the same time that the line was carrying data. That’s one of the reasons why DSL is the world’s most popular method of connecting to the Internet.

The most common DSL offering is designated ADSL Lite, or G.lite, which is an International Telecommunications Union (ITU)-sanctioned standard. It offers download speeds up to 1.5 Mbps and uploads at rates up to 384 Kbps. Full-rate ADSL is faster, offering a download rate of up to 8 Mbps and an uplink rate of 1 Mpbs.

But the full-rate standard is more than most residential users will need, and it requires that phone company installers install a special splitter on your phone line to separate the voice from data.

It also costs a lot more. One advantage of Telco DSL is that the medium is technically ready to go even faster than 8 Mbps.With refinements, future throughput might improve to 12 Mbps.

DSL service is limited to those lucky customers who happen to live within three miles of a central switching office (CO). The throughput rate will vary from ISP to ISP. The speed available to users is limited by line quality and distance. The typical 1.5 Mbps residential offering assumes a maximum length of 12-thousand to 17,500 feet.

The range limit for higher or symmetrical rates is less than that. Those near the end of the line may have to settle for less than top speed in any case. Some lines, though short enough and adequate for voice, may not be up to snuff for high-speed data. Even with a perfect new telephone line, the digital signal degrades over distance.

The high carrier frequencies deteriorate even more quickly when forced through loading coils that are installed to condition long lines solely for voice. Bridge taps are unconnected cables that remain spliced onto your telephone line, probably as leftovers from an old connection to a different subscriber.

They are notorious for soaking up data frequencies. If your home line attaches to a CO through a digital pairgain link, you cannot get DSL at all. Customers who have waited all day for a telephone repairperson to show up might worry about getting DSL service from the same source.

Usually, installers do most of their work outside the house and in the background. If they have access to the terminal block on the outside of your home, they can complete the final check without having you present.

If you should buy the DSL service from another entity, it is still the telephone company that runs a new copper line for the service up to your building, or to the demarcation point. Your DSL provider must then show up to do any inside work. Sometimes the two don’t communicate well under this arrangement.

ISP employees used to routinely show up and personally install DSL hardware and software at customer sites, but they learned that most customers were willing and capable of doing it themselves. Customers also prefer to save the service charges and forego delays.

The technical uncertainties concerning the DSL signal sometimes leave the phone company with a choice of either cleaning up your telephone line or turning you down as technically not feasible.

If they decide to overhaul the line in a process known as conditioning (they are not required to do so) and additional problems occur between the phone company and your chosen ISP, a couple of months may pass before you get a firm order commitment (FOC). This is the date at which outside wiring is scheduled to connect to your minimum point of entry (MPOE).

Your ISP should let you know when that is and whether or not you will have to be present to let the telephone installers into your yard. Depending on how the trunk lines are distributed, you may be eligible and your neighbor may be out of bounds. Fortunately, the phone company can send a test signal down the line before you buy.

This evaluation will usually, not always, prevent a disappointment when the delivery truck drops off your new DSL modem. Over time, the Telcos and ISPs are becoming better coordinated. Some of them can team up to deliver service in a week.

Different varieties of DSL modems are available, and the kind that connects to your telephone line will depend on the equipment your phone company uses at the other end of the line. If you do not select your phone company as your ISP, you may wait for your ISP to deliver the appropriate modem to you.

That can happen weeks after your telephone company says the line is ready. Even if you live across the street from a switching office there may not be any DSL equipment inside of it, ready and waiting for your connection.

Telephone companies are installing fiber, routers, and Digital Subscriber Line Access Multiplexers (DSLAMs) as fast as they can, or rather, as fast as they can afford to. But in order to bill the most new users first, they prefer to install in concentrated urban areas, so that a CO may be fully utilized from the day it goes online.

Smaller companies, known as Competitive Local Exchange Carriers (CLECs), have jumped into the race to grab and hold new customers, but if you live in a rural area, you still may have to wait until someone gets around to you.

Most ISPs provide a range of horsepower and service choices, bundling in extras such as multiple email addresses and personal web pages. The competition for new customers is so great that many are giving away the initial setup costs, the DSL modem, and throwing in a cut monthly rate as signup incentives.

Many actually lose money on the deal at first, hoping to gain profits if you stay happy and stay subscribed for years. Typically, $70 per month will get you 1.5 Mbps downstream. That price gets hiked if you declare yourself to be a business customer.

Shopping around will save you far more than it will cost. Although you may have trouble getting through on the tech support line, you will find that the salespeople will pick up their phones comparatively quickly.