A digital subscriber line (DSL) is an inexpensive Internet access option that transports high-speed data from your phone company’s central office to your company’s network. The data is transmitted over the same copper wires used by most phone systems.

DSL Internet service is very distance-sensitive. The closer your company is to the phone company’s central office – where phone lines connect to switching equipment – the faster your connection. It is generally recommended that your office be located within 2-3 miles of the central office for faster, more affordable service. Beyond 3 miles, you would only qualify for low-speed DSL service – if any at all.

You can find out if you are within range for DSL by calling your local ISP, or looking up your location online. There are many Internet sites that allow you to check if your area can get DSL and how fast a connection you qualify for.

Types of DSL
There are various types of DSL (referred to as xDSL). The two most common are Symmetrical DSL (SDSL) and Asymmetrical DSL (ADSL).

ADSL uses your existing copper phone lines to transmit data, but limits upload speeds to as little as one quarter of download speeds. SDSL is a more robust (and more costly) version of DSL that supports equivalent upload and download speeds. This is good for companies that regularly upload large files, but requires dedicated wiring.

A newer offering is VDSL (very high data rate DSL). VDSL speeds can range from 13 Mbps to 56 Mbps over short distances, usually between 1000 and 4500 feet (300 - 1500 meters), of twisted pair copper wire. The shorter the distance, the faster the connection rate.

The downsides of business DSL
Reliability is the primary concern with DSL Internet service. On average, the uptime for DSL isn’t as good as it is with a T1 connection. Service level agreements (SLAs) that ensure your connection will always be running are often not offered with DSL service. And while a DSL connection can support many simultaneous users for sending e-mail and surfing the web, it’s not optimal for applications requiring a lot of bandwidth such as large file downloads or streaming video.

DSL Internet service also runs into the problem of slow connections due to oversubscription – the act of selling more bandwidth than is actually available. DSL providers will sign up more subscribers than they have bandwidth for, with the expectation that not all users will be online at the same time. While you’ll get faster connection rates – up to 2 Mbps – when there aren’t a lot users online, your connection will lag when more customers connect. This can be highly frustrating, to say the least.

Even newer VDSL connections need to co-exist with other communications media and applications, and sometimes have to contend with cross talk and interference. This can present problems to businesses that depend on Internet access reliability for applications such as VoIP and video.

In the end, the savings you may gain from using DSL Internet service can be offset by how much you compromise critical business applications like an internally maintained e-mail server or web server.

Necessary equipment
Most business DSL customers use a router to connect their local area network (LAN) to the Internet. While more expensive than a standard DSL modem, a router provides data security and data filtering services, which are valuable in business environments. If you have fewer than 10 computers to connect, you can opt for a less expensive DSL modem, although you will still need to purchase firewall software to secure your network. Your DSL provider will lease or sell you the appropriate hardware.