A-law
One of the nonlinear encoding laws defined in G.711. Principally used for the public telephone network in North America.

ACF
An endpoint to gatekeeper message, meaning Admission ConFirmed

ADSL
Asymmetric Digital Subscriber Line. A transmission technique using existing copper wires from a telephone company to the subscriber with a modem at either end, which send high-speed digital signals with more information travelling from carrier to subscriber than in the reverse direction, hence asymmetric.

AEC
Acoustic Echo Cancellation. Used in videoconferencing systems to monitor input from open microphones and avoid echo or ‘howl-around’ by removing any signal output to the speakers from the CODEC’s input.

AES
Advanced Encryption Standard.

AGC
Automatic Gain Control. Helps to maintain audio levels in videoconferencing systems

AMX
Proprietary integrated control systems for AV applications. http://www.amx.com/

Analogue
Used to describe a continuously variable signal, as opposed to a discrete or ‘digital’ one, or a circuit designed to handle such signals.

ARQ
An endpoint to gatekeeper message, meaning Admission Request

Artifact
In video technology this refers to noticeable spurious effects occurring as a result of technical limitations

Asynchronous
Communication in which there is no synchronisation between transmitter and receiver. Each character is framed by a number of start and stop bits. Used by most terminals and many microcomputers.

AV
Audio Visual.

Audio
Signals that carry sounds.

Audio Bridge
Equipment that mixes multiple audio inputs and feeds back composite audio to each station after removing the individual station's input.

Automatic Bandwidth Adjustment
Algorithm in H.323 endpoint for automatic increasing and decreasing video bit rate due to the network behavior