xDSL

Also called DSL. Generic acronym coined for the many flavors of digital subscriber line access services provided by telcos (ILECs, CLECs, etc.) to their customers. The x stands for any one of a number of implementations: A = Asymmetric, H = High-bit-rate, R = Rate Adaptive, S = Symmetric or Single-line high-bit-rate, V = Very-high-bit-rate, etc. We can thank Bellcore (now Telcordia) for nearly all of the xDSL acronyms.

Let s start by getting two pieces of trivia out of the way: First, xDSL refers to the type of digital modem, not a line per se. Homes and companies already own ordinary copper pair lines. Put a pair of ADSL modems at either end of them, and you ve got an asymmetrical digital subscriber line. Put SDSL modems on the same line and you ve got SDSL service instead of ADSL. Same line, different modems. So, DSL is a modem, not a line, and a line needs two modems for there to be a service.

Trivia item number two: Originally, way back in the mists of time, the term DSL itself meant the modem used for Basic Rate ISDN, which was considered as futuristic in its day as ADSL and its cousins are now.

In any case xDSL can carry duplex voice and data simultaneously, as well as the signaling data used for call information and customer data. xDSL routing equipment uses digital coding techniques to more efficiently transfer data over traditional copper phone lines. Most xDSL services are data only ...