Telecommunications Terms Glossary

ADSL

Asymmetic Digital Subscriber Line. A digital line that uses the existing twisted pair copper telephone network to achieve speeds of up to 6 megabits per second up to 12000 feet, or 1.5 megabits per second up to 18000 feet.

asymmetrical

Providing differing bandwidth in different directions. 56 K modems are asymmetrical: they offer a maximum speed of 56K for downloading, but only 28.8K or 33.6K for uploading.

baud

A measure of signal changes per second. Often used incorrectly in place of bps (bits per second).

bps

bits per second.

BRI

Basic Rate Interface. A consumer grade ISDN line consisting of 2 64K bearer channels and one 16K delta (controller) channel.

CLEC

Competitive Local Exchange Carrier. An alternative to the existing local phone company.

CCITT

International Consultative Committee on Telecommunications and Telegraphy. The CCITT acronym comes from the French Commite' Consultatif International de Telegraphique et Telephonique. An international standards body. Known as the ITU-T since March 1, 1993.

CO

Central Office, in reference to the phone company's central switching station for a given area.

demodulation

Converting analog signals back into digital signals. A modem is a MOdulator/DEModulator.

DS1

A high-speed line capable of delivering 1.54 Mbps (1,540K) in both directions, and divided into 24 data-bearing channels.

DS1C

A high-speed line capable of delivering 3.15 Mbps (3,150K) in both directions.

DS2

A high-speed line capable of delivering 6.31 Mbps (6,310K) in both directions.

DS3

A high-speed line capable of delivering 44.7 Mbps (44,700K) in both directions.

DSP

Digital signal processor. A specialized processor, usually for handling audio or video signals.

DSVD

Digital Simultaneous Voice and Data.

E-1

Roughly the European equivelant of a T1 or a PRI, but with 30 data-bearing channels

FIFO

First In, First Out. A type of data buffering that prevents data loss during high-speed communications.

HSP

Host signal processor. In modems, a modem that depends on the host CPU (the Pentium, PowerPC, etc., in the main computer) for part or most of the data processing.

hybrid

A device that converts the two-wire local loop to the four-wire central office.

ISDN

Integrated Services Digital Network. A digital phone service capable of speeds from 57.6 K to 128 K. Provides two data channels, each with its own phone number, making simultaneous voice and data possible.

ISP

Internet Service Provider. A company that provides access to the Internet through modems, ISDN, T1s, etc.

ITU

International Telecommunications Union. An international standards body. Known as the CCITT prior to March 1, 1993.

K56flex

Lucent and Rockwell's joint 56K modulation protocol that makes Rockwell's K56Plus and Lucent's V.flex2 technologies interoperable

K56Plus

Rockwell's proprietary protocol for 56000 bps modulation. Merged with Lucent's V.flex to create K56flex.

Kbps

kilobits per second. KBps is kilobytes per second.

local loop

The copper wires running between the telephone subscriber's home or business and the phone company switch.

Mbps

megabits per second. MBps would be megabytes per second.

Modem

A MOdulator/DEModulator. A device that can encode digital signals from a computer into analog signals that can be transmitted over analog lines, and vice versa.

modulation

Converting digital signals into analog signals. A modem is a MOdulator/DEModulator.

OC-3

A fiber optic line capable of 155 megabits per second (155,000K).

OC-48

A fiber optic line capable of 2400 megabits per second (2,400,000K).

PCM

Pulse Code Modulation. A method of encoding an audio signal in digital format.

PCMCIA

Personal Computer Memory Card International Association. A standard for miniturized laptop expansion cards for modems, storage, and other devices. Often called PC cards.

POP

Point of Presence. A local dialin point for an Internet Service Provider.

POTS

Plain Old Telephone Service. Regular analog phone service, as opposed to ISDN, ADSL, and other digital phone services.

PRI

Primary Rate Interface. An industrial grade ISDN line. In the United States and Japan, a PRI consists of 23 64K bearer channels and a 64K delta (controller) channel. In Europe, a PRI consits of 30 bearer channels and a delta channel.

PSTN

Public Switched Telephone Network.

RBOC

Regional Bell Operating Company.

RPI

Rockwell Protocol Interface. A type of HSP modem that is limited to 14.4 connections.

symmetrical

providing equal speeds in both directions. Compare with asymmetrical.

T-1

In North America, a digital carrier for a DS1-formatted signal.

T-3

In North America, a digital carrier for a DS3-formatted signal.

UART

Universal Asynchronous Receiver-Transmitter. A controller chip that processes data coming in and going out of the modem. The 16550 is a modern example.

V.32terbo

AT&T's proprietary protocol for 19200 bps asynchronous communications.

V.32bis

The ITU standard for 14400 bps modulation.

V.34

The ITU standard for 28800 bps modulation.

V.90

The ITU standard for 56K modulation.

V.FC

Rockwell's proprietary protocol for 28800 bps asynchronous communications.

V.flex

Lucent's proprietary protocol for 56000 bps modulation. Merged with Rockwell's K56Plus to create K56flex.

x2

U.S. Robotics' proprietary protocol for 56K modulation.

Glossary of Telecommunications Terms