On the surface, SDSL and cable appear very similar. Both use established networks and existing lines to deliver high-bandwidth Internet access. But the similarity ends there.

Cable Modems: Broadcast Technology
Bandwidths Vary
The existing cable network is optimized for broadcasting programming to a large number of end users. Since all users in an area share the bandwidth of a single cable line, the actual available bandwidth can vary widely. When a large number of people are online, or when some people are downloading video or uploading large files to the Internet, actual bandwidth can slow to speeds less than the average dial-up connection.

Interference
An occasional problem with cable Internet access is interference. The downstream (downloading) communication channel is relatively free from interference by other channels. However, the upstream communication channel (uploading to another site) tends to suffer from interference by other devices in the area (CB radios and cabling infrastructure in and around the home).

SDSL: True Network Technology
You Get What You Pay for
Symmetric Digital Subscriber Lines (SDSL) are unique lines all the way to the Central Office or Public Switched Telephone Network (PSTN), where traffic is directed onto the Internet. This means that, similar to ISDN and T1 lines, the SDSL bandwidth you pay for is the bandwidth you get.

Uploads as Fast as Downloads
Cable Internet access is asymmetric, meaning it provides more bandwidth for downloads than for uploads. This is fine for home use, because people are usually bringing in files for information or entertainment. But asymmetric bandwidth can hinder business communication by cramping video conferences and slowing the transfer of large files.

SDSL, as the name states, is symmetric, providing the same bandwidth for uploads and downloads. Symmetric bandwidth is essential for businesses that frequently deal with large files, use video-conferencing technology, or serve files to the Web.

Easier, Less Expensive Installation
Finally, while the cable network is in place and installed in most homes, few businesses have cable access installed at all, and very, very few have coaxial cable outlets in every office. So, using cable for Internet access means installing cable service and running coaxial cable to every room in which Internet access is needed.

Because SDSL uses existing copper phone lines, installation is much simpler—and less expensive. Look at your walls. Wherever there's a phone jack, you can have a connection to the Internet using SDSL technology.