DSL Crib Sheet
Digital Subscriber Line (or Loop) technology provides high-speed, broadband network connections to homes and small businesses. DSL utilizes the same cabling used for normal telephones, but it can offer higher data rates... ... through use of so-called digital modem technology. Still a relatively new technology that telephone companies and other access providers are in the process of deploying for the first time, DSL remains unavailable in many locations. Some customers already subscribed to DSL -- so-called "early adopters" -- have experienced the growing pains of this very promising network service.
Technology - The Modem Pair
Technically speaking, the term "Digital Subscriber Line" is misleading in that modems comprise the heart of this technology and the lines themselves are actually just plain telephone lines. From a customer's point of view, their DSL modem (that they've purchased as part of the service) talks to another DSL modem somewhere at the provider's location, but the telephone line itself doesn't change. In fact, it's possible for DSL subscribers to share the same line for their digital and analog traffic. You can keep surfing the Web while waiting for that phone call from your boss!
More technology details (pg. 2)
Availability - How Near is Your Exchange?
The technology used to implement DSL only works over a limited physical distance. At the maximum, DSL runs about 18,000 feet (3.5 miles or 5.5 kilometers) from a telephone exchange. Without going into to all the details of public exchanges, suffice it to say that companies in the United States historically did not install them this close to homes in some suburban and many rural areas. Several variations on DSL technology constrain these physical cable distances even further -- down to as low as 1,000 feet (0.2 miles or 0.35 kilometers). They do this in order to offer even faster network speeds.
More availability details (pg. 3)
Variations - The DSL Family Tree
People sometimes refer to Digital Subscriber Line (DSL) services as "xDSL" services. This happens because the term DSL refers to a group of related networking technologies rather than just one. Due to the way in which these technologies evolved historically, a good metaphor for xDSL is a family tree.
DSL customers, though, probably don't care much about history and have much more interest in availability and features. In this sense, xDSL may be better compared to a restaurant menu. It doesn't yet have 31 famous flavors in production like Baskin-Robbins, but xDSL does emcompass many varieties: ADSL, HDSL, SDSL, and VDSL just to name a few.
More variation details (pg. 4)
Customer Experience - Some Growing Pains
Some customers have reported difficulties in transitioning to DSL service. Once DSL is ordered, it can take a surprisingly long amount of time to have the service successfully installed. Once installed, some customers report that the technology sometimes works unreliably -- dropping connections unexpectedly, for example.
More customer experience details (pg. 5)
Overall
DSL technology promises to relieve the "World Wide Wait" syndrome that many on the Internet still complain about. Access providers will need to continue improving their new technologies and upgrading their existing cabling. Competition for cable modems and other sources will exist. But compared to standard analog modems, xDSL will be a welcome addition to many home and small business networks for years to come.
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