Asymmetric, or unbalanced, refers to the common practice of having two transfer rates: a fast one (typically 768 Kbps to 1.5 Mbps) for information flow into your net (the downlink) and a slower uplink speed (384 Kbps) for data outbound to the net.

Residential ISPs operate that way regardless of the transmission media because it’s cheaper, and most home users only transmit when they are requesting data. Those requests are brief and usually come through the computer keyboard.

Since most of us cannot type at 187,000 characters per second, a slower line speed for that function is more than adequate. Perhaps the only time you will notice the difference is when you forward a mail message with a long file attached. It will take longer to send than it took to receive.

A home-based business operator (someone with a web server in his or her back room, for example) may want to send information to customers with a wide-open throttle. A symmetrical DSL (SDSL) link is available to them—for a price, of course. The speeds we will quote represent the best case.

Most ISPs cover themselves by promising a best effort to achieve them. A sad fact about networks generally, including Wi-Fi, DSL, and ISPs alike, is that providers often measure throughput with a rubber speedometer. At least 13 percent of their stated maximum will be lost through overhead costs. Individual circumstances do vary.

If the uplink is saturated to capacity by sending a large file, then the downlink can drop to almost the same speed. That’s due to a builtin deficiency in the Internet Protocol (IP), and all ISPs are subject to it. Cable Internet is more vulnerable because all the users on a single cable segment must share the uplink.

The Data over Cable Service Interface Specification (DOCSIS) recommended maximum is 1,000 users per segment. It’s not hard to see why ISPs are intolerant of users who provide some kind of nonstop streaming service, such as webcasting MP3s on a residential line. It only takes a few so-called abusers to set off a traffic jam.

Whether your data is delivered over cable television or telephone lines, your DSL provider will not necessarily be the same as your ISP. If you have an email address that all your friends are familiar with, you may want to keep your dial-up ISP and simply upgrade the service to DSL.

If you do, most ISPs will let you keep on using your dial-up for a few hours a month (20, typically) either as an emergency backup for the DSL link or as a way of checking your email from a hotel room. They’ll let you use it as much as you like usually, if you are willing to pay for the extra service.

Unlike plain old telephone service (POTS), DSL quality of service (QoS) is not regulated by a state agency. If your link is giving you grief, you cannot call the Public Utilities Commission (PUC) to complain about it. Actually, thousands and thousands of irate customers do so anyway every year to no avail.

ISP dedication to customer satisfaction can vary unpredictably. Providers are caught in a perennial squeeze between falling revenues, intense competition, and the urge to claim as many new customers as possible, for new customers are easier to acquire than someone else’s.

Users cannot assume that their provider will be as permanent or as well equipped as the telephone companies they are familiar with. For that matter, after the bankruptcy of WorldCom and newsreel footage of Adelphia executives being led off in handcuffs, users cannot assume the permanence of their phone companies or ISPs.

Most providers will insist that new customers commit for an extended period of time, in order to qualify for signup incentives. But it was only in 2002 that ISPs were required to warn their customers at all when the provider decided to go out of business.

The restriction was a legislative response to service providers that quit during the dot-com collapse of the late 1990s, such as North Point Communications of San Francisco, which suddenly abandoned users when going out of business.

In such a circumstance, it actually takes longer for a user to transfer to a new provider than for the initial signup and installation. You can go to places on the Web in advance of signing a DSL contract to get independent estimates of their service and track record. One such is www.dslreports.com. They provide several services, including:

• Helpful installation and troubleshooting tips
• News items about the cable and DSL industries, and government regulation
• Service locators for your area
• Frequently asked questions
• Tweaks and adjustments to boost speed
• Forums and opinion polls
• An automated security check of your system

It costs you nothing to look, and when you see their criteria and a few sample track records, you will form your own questions to ask. It also costs you nothing to listen. As the old saying goes, “Ask the person that owns one.” Your neighbors or coworkers may have tales to tell you.

You should also remember that any prices we quote here would vary from week to week, as vendors compete and special offers come and go. They are intended only as a general guide. You will have to check vendors’ web pages individually to be sure.With prices generally declining, you may be pleasantly surprised.

If broadband Internet Service is as fast as everyone claims, you may be wondering if your old 486-type microprocessor can keep up with it. The short answer is yes. The long answer is that it all depends on what you plan to use the Internet to do.

If you plan on interactive 3-D games, your old clunker may fall behind, but the problem will be the PC’s video card or processor against the complexity of the application, not an excess of data spilling over. For most applications such as web browsing and email, an older machine will do just fine.