Understanding Your DSL Internet Connection

If you've recently signed up for DSL internet — or you're thinking about making the switch from dial-up — you probably have some questions about how this technology actually works. DSL, which stands for Digital Subscriber Line, is one of the most widely available forms of broadband internet in the United States today. Unlike dial-up, it gives you an always-on connection and lets you use the phone and the internet at the same time.

Let's break down what DSL is, how it works, and what you should realistically expect from your connection.

How DSL Works

DSL internet travels over the same copper telephone wires that carry your regular phone calls. The key difference is that DSL uses a much wider range of frequencies than voice calls do. Your telephone conversation only uses a small slice of the available bandwidth on the copper wire, and DSL takes advantage of the unused frequencies to transmit data.

When you sign up for DSL service, your provider installs a device called a DSLAM (Digital Subscriber Line Access Multiplexer) at the local telephone exchange — often called the "central office." This equipment communicates with the DSL modem in your home. The connection between these two points is your DSL line.

Because DSL runs on existing phone infrastructure, it's available nearly everywhere that phone service exists. That's a major advantage over cable internet, which requires separate coaxial cable infrastructure that isn't present in every neighborhood.

ADSL vs. SDSL: What's the Difference?

You'll often see two acronyms when shopping for DSL: ADSL and SDSL. The "A" stands for Asymmetric, and the "S" stands for Symmetric. The difference comes down to how bandwidth is divided between uploads and downloads.

ADSL (Asymmetric DSL) provides faster download speeds than upload speeds. This is the most common type of DSL service available to residential customers. A typical ADSL connection in 2005 might offer download speeds between 1.5 and 6 Mbps, with upload speeds of 384 Kbps to 768 Kbps. ADSL makes sense for most home users because we tend to download far more data than we upload — loading web pages, downloading email attachments, and so on.

SDSL (Symmetric DSL) provides equal upload and download speeds. This type of service is more common in business settings, where employees may need to upload large files, host web servers, or run VPN connections. SDSL typically costs more than ADSL and may not be available in your area for residential use.

For the vast majority of home users, ADSL is the right choice. Unless you're running a small business server from home or regularly uploading very large files, the asymmetric allocation of bandwidth is a good fit.

What Speeds Can You Expect?

Here's where it gets complicated. DSL speed depends heavily on one factor: your distance from the telephone company's central office. The farther your home is from the DSLAM, the weaker the signal and the slower your connection.

If you live within about 5,000 feet of the central office, you can expect speeds at the higher end of what your plan advertises — potentially 3 to 6 Mbps for downloads. At 10,000 feet, those speeds may drop to 1.5 to 3 Mbps. Beyond 15,000 feet, DSL service may be slow enough that it barely beats dial-up, and at around 18,000 feet, it may not work at all.

Your provider should be able to tell you how far you are from the central office before you sign up. Some providers also have online tools where you can enter your address and get an estimate of available speeds.

Other factors that affect DSL performance include:

• Quality of the phone wiring in your home and between your home and the central office
• Line interference from nearby electrical equipment or poor connections
• The age of the copper lines in your neighborhood
• How many other DSL subscribers are on the same DSLAM

DSL Filters and Installation

When you get DSL installed, you'll receive small devices called DSL filters, or microfilters. These plug into every phone jack in your house that has a telephone connected to it. The filters separate the DSL signal from the voice signal, preventing the buzzing and static that would otherwise interfere with your phone calls.

Your DSL modem plugs into a phone jack without a filter — or into a dedicated, filtered jack installed by the technician. The modem then connects to your computer, either directly via an Ethernet cable or through a router if you want to share the connection among multiple computers.

Installation is usually straightforward. Many providers offer self-installation kits that include the modem, filters, and cabling. If you're not comfortable setting it up yourself, you can schedule a professional installation visit, though this typically costs extra.

Tips for Getting the Most From Your DSL

A few practical suggestions for new DSL subscribers:

• Install filters on every phone jack that has a phone or fax machine connected. Missing a filter is the most common cause of connection problems and line noise.
• Use a short, high-quality phone cable between the wall jack and your DSL modem. Longer cables can degrade signal quality.
• Keep your modem away from other electronics that might cause interference, like cordless phone base stations, microwaves, and CRT monitors.
• Check your inside wiring. If your house has old or damaged phone wiring, it can significantly affect DSL performance. Replacing an old phone cable run with new wiring can sometimes improve speeds noticeably.

Is DSL Right for You?

DSL is an excellent choice for most home internet users in 2005. It's widely available, reasonably priced, and fast enough for web browsing, email, and downloading files. The always-on connection is a massive upgrade from dial-up, and the ability to use your phone line simultaneously is a genuine quality-of-life improvement.

If you're in an area where cable internet is also available, it's worth comparing the two. Cable generally offers higher top-end speeds, but DSL provides a dedicated line that isn't shared with your neighbors — meaning your speeds are more consistent throughout the day.

For most households, a DSL connection in the 1.5 to 3 Mbps range is more than sufficient for current needs. As more bandwidth-intensive applications emerge in the coming years, the broadband landscape will continue to evolve — but for now, DSL remains one of the most practical ways to get online at broadband speeds.