This glossary is intended to provide a practical, nontechnical understanding of some common videoconferencing terms. For precise technical or legal definitions of these terms, please refer to the Web sites or publications of the appropriate organizations, regulatory bodies, and experts listed in Appendix B.

Numbers

4CIF

Four times common intermediate format. An optional high-resolution format (in H.263) for the transmission and display of a picture consisting of 704 x 576 pixels.

10Base-T

10 Mbps Ethernet LAN technology.

100Base-T

100 Mbps Ethernet LAN technology.

A-B

A-D

Analog-to-digital conversion.

ADPCM

Adaptive differential pulse-code modulation. An audio coding technique used in G.728.

ADSL

Asymmetric digital subscriber line. A high-bandwidth network technology that transmits at a higher rate in one direction than the other. Uses conventional copper telephone wiring for bandwidths of up to several Mbps.

AGC (Automatic gain control)

A circuit or algorithm that normalizes a signal (e.g., voice or video) regardless of the amount of light or sound.

A-V (Audio-visual)

Usually refers to a system or application that involves the simultaneous use of both media, audio and video.

Aggregation

Method for sending data down two or more parallel channels.

A-law

European PCM compression method for digital voice communication.

Algorithm

A mathematical formula or program intended to perform a specific task (e.g., compressing video or encrypting data).

Analog

The conventional method of recording or transmitting audio and video. Usually employs continuously variable amplitude or frequency (corresponding to some characteristic of the original signal) to convey information.

Analog overlay systems

Video distribution and...