Digital Subscriber Line (DSL) technology-which has been hyped for the last two years-is becoming more widely available as an option for connecting libraries to the remote central site of an automated library system or to an ISP, but it remains confusing. There are nine different varieties of it. While all use copper telephone wires already installed for normal telephone service, only one, SDSL (Symmetric DSL), offers equivalent downstream and upstream data transmission rates.
Other types of DSL, which include ADSL, CDSL, IDSL, and VDSL, transfer much faster downstream than upstream. Symmetry is not necessary to access an ISP, but it is essential when connecting libraries to the remote central site of an automated library system.
At 1040 Kbps, SDSL appears to offer about 70 percent of the bandwidth of a full T-1 circuit. However, most SDSL users report their performance to be less than 70 percent of that of a full T-1 circuit. Nevertheless; the smaller bandwidth meets the needs of the vast majority of libraries.
The two major drawbacks to DSL are its spotty availability and wide variations in pricing. While DSL is available in and around most major cities, SDSL is not available in some of these. Other types of DSL, some of which offer data rates as low as 256 or as high as 1500 Kbps, are more widely available.
Monthly service prices range from as low as $119.95 to as high as $1,600. Currently, the low-cost providers are US West and Bell South, with UU Net being the high-cost provider. These monthly rates do not include installation charges-under $225 for US West and Bell South, $3,000 or more for Infinite Data Source and UU Net. In addition, there are the costs of the required modems for connecting standalone workstations or the routers for connecting LANs.
DSL providers are constantly adjusting prices in response to demand and competition. There is an increasing tendency to differentiate between home and business users, with the latter charged much higher rates for the same service. Most DSL providers do not offer the same service guarantees that are commonly offered for other leased telco circuits.
Not only should a library compare all of the DSL options available in its area, but also the competing options.
These include dual analog (112 Kbps), ISDN (128 Kbps), fractional and full T-1 (64 to 1400 Kbps), and cable modems (56 to 10,000 Kbps).
