The definitions that follow will help you wade through the telecommunications alphabet soup. Note, however, that some terms may vary with the service provider.

ATM: Asynchronous transfer mode, a switching technology used for high-speed transfer of digital data. Asynchronous means that downloading and uploading speeds may vary.

Backbone: The backbone is a set of paths or transmission lines that local or regional networks connect to for long-distance or wide area networking.

Bandwidth: The amount of space available to transmit information. When it comes to bandwidth, bigger is better — size dictates how much and how fast voice, video and data can travel through a conduit.

Bit: A contraction of binary digit. The smallest unit of information that a computer can process. It's the basic unit in data communication.

BRI: Basic rate interface. For home and small business ISDN use, BRI consists of two 64 Kbps "B" ISDN channels and one 16 Kbps "D" ISDN channel. It might cost a small business about $130 for installation, $300 for the ISDN adapter and about $20 per month for the line that supports the ISDN.

CLEC: Competitive local exchange carriers, local telephone service providers that compete with the ILECs (incumbent local exchange carriers). CLECs was a term coined by regulators to distinguish them from ILECs after passage of the 1996 Telecommunications Act. CLECs must be approved by the State Corporation Commission prior to offering services. Many CLECs buy service from ILECs and resell it to consumers.

Coaxial cable: Often used by cable television companies, coaxial cable has a physical channel that carries the signal and another physical channel that serves as the ground. It can be used by businesses for Ethernet and other LAN connections and is also used by some telephone companies to connect from the central building to user telephone poles.

DSL: Digital subscriber line. High-speed transmission of information, data, video and voice. ADSL travels across copper wire from modem to modem. HDSL travels across a T-1 line. XDSL is the generic reference to DSL.

Ethernet: A form of LAN backbone technology that provides for high-speed data transmission from one workstation to another.

Frame relay: An economic way to transmit data between LANs and WANs. Frame relay places data in frames, which speeds up overall transmission. With frame relay, the customer has a continuous, dedicated connection without paying for a full-time leased line.

FTP: File transfer protocol, a program for exchanging files with a Web server, also known as a virtual host.

ILEC: Incumbent local exchange carrier, serving a designated region. Prior to the passage of the 1996 Telecommunications Act, ILECs such as GTE and Bell Atlantic were the only providers in their designated regions. The act called for competition, which led to the development of competitive local exchange carriers, or CLECs.

ISDN: Integrated services digital network is a set of digital transmission protocols for digital transmission over ordinary telephone copper wire and other transmission media. ISDN can be installed in place of a more traditional modem for high-speed transmission of data. With ISDN, there are two levels of service, the basic rate interface (BRI) and the primary rate interface (PRI).

ISP: Internet service provider, a company providing individuals and businesses access to the Internet, usually for a monthly fee. An ISP has the telecommunication lines and equipment required to have a POP (point-of-presence) on the Internet for the area or region it serves.

LAN: Local area network, a network of interconnected work stations sharing the resources of a single server.

LMDS: Local multipoint distribution service uses a fixed, mounted antennae to pick up a microwave signal for high-speed transmission of voice, data and video.

Local loop: Generally the wired connection from a telephone company's central office to customers' phones.

PCS: Personal communications services, a generic name for any mobile voice or data telecommunications service.

POTS: Plain old telephone service. Twisted pair copper wires that transmit voice from one point to another along a designated physical path.

PRI: Primary rate interface. For larger business ISDN users, PRI channels are carried over a T-1 line. U.S. users get 23 "B" channels and one "D" channel.

RBOC: Regional Bell operating company. In 1984, when Ma Bell was split up, there were seven regional Bell operating companies created for local telephone service. Due to mergers there now are four, one of which is Bell Atlantic.

TCP/IP: Transmission control protocol/Internet protocol. This is the Internet's two-layered communication language. TCP manages messages and files by breaking data into smaller packets and reassembling it when it reaches the receiver. IP makes sure the packets get to their destination, rechecking the address at each gateway on the network.

T-Carrier system: Introduced by Bell. In its original version, the T-1 line transmitted 1.544 Mbps and is widely used today for Internet connections. Since the T-1 was created in the 1960s, there have been advances. The T-3 line provides transmissions at 44.736 Mbps.

WAN: Wide area network. This telecommunications network often spans a large geographic area, and access is frequently shared among public and private users.

Compiled by Kathleen F. Phalen

Sources: GTE, Bell Atlantic, James Madison University, Voice and Data Communications Handbook, IBM Dictionary of Computing, Newton's Telecom Dictionary.