Appendix A. Definitions - Vidyo VidyoGateway Administrator's Manual

Appendix A. Definitions

This chapter defines the terms used in this guide with which you may not be familiar.
For more standard VidyoConferencing definitions, refer to the
Guide.
 AGC – Automatic Gain Control. In a VidyoConference with VidyoGateway version 2.2, AGC
automatically controls the gain of a signal by reducing the volume if the signal is strong and
raising it when the signal is weaker, thereby keeping the audio output at a near constant level.

AVC – Advanced Video Coding. AVC is also known as MPEG-4 Part 10 or H.264. See also
Protocol (H.264/AVC).
 CIF Protocol – Common Intermediate Format. A video format used in videoconferencing
systems that supports both NTSC and PAL signals. CIF is part of the ITU H.261
videoconferencing standard. It specifies a data rate of 30 frames per second (fps), with each
frame containing 288 lines and 352 pixels per line.
 Codec – Short for coder/decoder or, because codecs are commonly used for compression,
compressor/decompressor; a codec is any technology for compressing and decompressing
data. Some popular codecs for computer video include MPEG, Indeo, and Cinepak.
 Cluster – A group of VidyoGateways used for increased capacity. One VidyoGateway is
designated the Controller. In addition to handling calls itself, the Controller also controls a
number of Standby VidyoGateways.
 Controller – A VidyoGateway that, in addition to handling calls, allocates capacity for a number
of Standby VidyoGateways.

Firewall – A system designed to prevent unauthorized access to or from a private network.
 Gatekeeper – A management tool for H.323 multimedia networks. Depending on the demands
of the specific network, the gatekeeper oversees authentication, authorization, telephone
directory, and PBX (private branch exchange) services, as well as call control and routing.

HD (High Definition) – A video format with a 1280 x 720 resolution and a 16 to 9 aspect ratio.
(There are other HD formats but this is the one referred to in this document.)
 Legacy System – In this guide, any videoconferencing system based on the SIP or H.323
protocol.
 MCU – Multipoint Control Unit. A device in videoconferencing that connects two or more
audiovisual terminals together into one single videoconference call. The MCU collects
information about the capabilities of the systems at each of the videoconference endpoints
and sets the conference to the lowest common denominator so that everyone can participate.
 NAT – Network Address Translation. An Internet standard that enables a local area network
(LAN) to use one set of IP addresses for internal traffic and a second set of addresses for
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