Digital Subscriber Line

A Digital Subscriber Line (DSL) connection uses existing copper telephone lines to connect homes and small businesses. Because the DSL line can carry voice and data, you do not lose access to your phone line when using your computer. DSL's always-on technology (well sort of) provides high-speed access comparable to cable modem access. Speeds typically range from 512Kbps to 1.544Mbps for downloads and slower for uploads, around 128Kbps. (The change in speed holds true for cable modems also; upload speeds are typically slower than download speeds.)

Consumers can have dynamic or static IP addresses for DSL. A static address remains the same over time, whereas a dynamic address can change every time you log in. In some cases, you pay extra for a static address. Many small businesses purchase static IP addresses because you can buy faster connections and still pay less than it would cost for a full or fractional T1 connection for a business. For the consumer, this means that you have several choices for using DSL, if it is available in your neighborhood.

Setting up a home DSL is an easy self-installation process. Like the cable modem, you have to purchase or rent a DSL modem, connect it to your phone line and your computer, install some software, and you should be ready to go.

DSL-only providers around the U.S. and larger companies such as the phone companies are slowly providing more DSL coverage. ISPs resell the DSL service of the major providers. To get DSL, you must live within two to three miles of the local phone company's switching facility. This can be a problem for people living in the middle of nowhere. Being further away from the telephone facility can have the effect of slowing down your connection speed. Cable modem access is far easier to get than DSL because the cable companies have a wider range of coverage, although this is changing. With the failures of DSL companies such as Covad, people are having even more trouble connecting through DSL because few competing DSL providers exist in the same market. If one DSL provider goes out of business, there might not be another in the same market to provide service.

DSL is obviously better than dial-up access and Integrated Services Digital Network (ISDN) connections, which max out at about 128Kbps. Because you are not sharing a network with others in your community, you don't have to fear sniffing of your traffic on the LAN as you would when using a cable modem. Also, the lack of sharing means that your connection speed won't degrade when other people in your area go online.

DSL comes in several flavors. Sometimes you can actually get a choice of what type of DSL service you get, and other times you have only one option, as is periodically the case in choosing cable access. One option is Asymmetric Digital Subscriber Line (ADSL), which provides fast download rates up to 1.544Mbps and upload rates from 128Kbps to 512Kbps. Symmetric Digital Subscriber Line (SDSL) has both fast upload and download rates, and is used more in businesses. Another option is Universal ADSL, which does not require a splitter to separate voice and data traffic. The following are other forms of DSL that you probably won't see:

• ISDN DSL (IDSL), which is a version of ISDN

• High-bit-rate Digital Subscriber Line (HDSL), which is fast and symmetrical

• Rate-Adaptive Digital Subscriber Line (RADSL), which determines DSL connection speed by how fast data can travel on your individual phone line

Cable and DSL rates are rather similar. The monthly fees can range from $30 to $150 depending on the speed you choose and the type of DSL connection you have, the rental charge of the DSL modem, and the setup fee. You can typically get DSL through your phone company, but you don't have a choice of provider. With a local ISP, you probably will be given a choice or providers. National providers also have service that you can use. An example of such a provider is DSL.com. The hit to the DSL market has caused failures of some national companies, one of which was Flashcomm. Going out of business can seriously affect your service!

Limitations

Like cablemodems, DSL does have its drawbacks. One main drawback for the consumer can be cost. It's easy to run up a high monthly fee if you choose a fast connection speed rather than the basic DSL packages. Another potential problem is connection slowdowns. Although it's not as easy to slow down the speed, electromagnetic noise and distance from the telecommunications facility can affect the DSL modem. In many cases, the IP address you get will be dynamic unless you request and possibly pay for a static address. This can be good because you won't be a static target for hackers, but you could have a hard time setting up a Web server address. And as with every other type of connection that consumers get, few DSL companies take responsibility for helping you secure your computer against attacks. Although some providers do take some measures to protect you, such as by warning you against hacking and providing information on security, it is still up to you to secure your system. Only recently have some providers, such as EarthLink, begun adding security software such as personal firewalls to their connectivity. Rather than just providing you an account and access, they help you secure your PC by providing some additional software.