April 1998

xDSL Glossary

Copper Applications in Electronic & Communications

When one dabbles in the alphabet-soup world of telecommunications, one is instantly inundated by acronyms. This article is no exception. Following is a small sampling of the acronyms one might run across in reading about xDSL technology. All the acronyms used in this article are included, but there are hundreds more in the industry.

xDSL Digital Subscriber Line technologies, with x denoting any of the various varieties, as follows:
ADSL Asymmetric Digital Subscriber Line, with a larger portion of the capacity devoted to downstream communications, less to upstream. Typically thought of as a residential service.
DSL Digital Subscriber Line technology, on which all the variations in this listing are based. Sometimes used to refer only to the earliest forms of the technology.
HDSL High-bit-rate Digital Subscriber Line, a technology for the business market in commercial operation several years, and using two wire pairs with 1.5 Mbps each way.
IDSL ISDN-based Digital Subscriber Line
RADSL Rate-Adaptive Digital Subscriber Line, where the DSL equipment senses the speed limitations of the customer's phone line and adjusts the rate downward accordingly from some maximum.
RDSL same as RADSL.
SDSL Symmetric Digital Subscriber Line using one pair, typically with about half the speed each way when compared to HDSL.
VDSL Very-high-bit-rate Digital Subscriber Line, with speeds up to 50 Mbps, but for only short distances, perhaps 1000 or 2000 feet at the highest rates of transmission.
ADSLF ADSL Forum, a group of several hundred companies involved in some way in DSL technology, formed to identify and solve technical and market problems and issues and to encourage standards, using a generic approach.
CAP means one of two things:
  1. Carrier-less Amplitude/Phase modulation, one of the line codes, or modulation systems, used for xDSL.
  2. Competitive Access Provider, company that competes with traditional phone companies. Usually means the same as CLEC.
CLEC Competitive Local Exchange Carrier, company that typically leases capacity from the local telephone company and resells it. In some cases these companies have networks of their own, such as in large cities.
DMT Discrete Multi-Tone, one of the line codes, or modulation systems, in which incoming data are spread over a number of channels of the available spectrum in an efficient way.
DSLAM Digital Subscriber Line Access Multiplexer, the piece of DSL equipment at the telephone company end of the phone line, usually in a central office.
ILEC Incumbent Local Exchange Carrier, such as any of the regional Bell operating companies or GTE.
ISDN Integrated Services Digital Network, an alternative method to simultaneously carry voice, data and other traffic, using the switched telephone network.
ISP Internet Service Provider, company which provides connection to the Internet, typically piggybacking on the local telephone company's wires.
IXC Inter-Exchange Carrier, typically a long-distance telephone company.
LAN Local Area Network, a wiring system to connect computers together within a company, a building or other local area.
LEC Local Exchange Carrier of whatever variety. It should be noted that there are more than 1000 such carriers in the USA in addition to the five RBOCs and GTE.
PSTN Public Switched Telephone Network, over which voice traffic moves.
RBOC Regional Bell Operating Company, of which there are five: Ameritech, Bell Atlantic, BellSouth, SBC Communications and U S West.
STP Shielded Twisted Pair copper wires, more common in Europe. Each pair may be separately shielded, or the entire cable or sections of the cable may be shielded to protect against outside interference.
TP Twisted Pair copper wires, where the twist provides protection against crosstalk or other interference.
UAWG Universal ADSL Working Group, a group formed in late 1997, and made up of Intel, Compaq, Microsoft, the five RBOCs and others, to move a specific version of xDSL technology to market quickly.
UTP Unshielded Twisted Pair copper wires, typically used in the USA.
VLSI Very Large Scale Integration, a high-speed chip technology.

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