Virtual Conferencing Glossary

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G.711 - An ITU-T Recommendation entitled, "Pulse Code Modulation (PCM) of Voice Frequencies". G.711 defines how a 3.1 kHz audio signal is encoded at 64 kbps using Pulse Code Modulation (PCM) and either mu-law (US and Japan) or A-law (Europe) companding.

G.721 - An ITU-T Recommendation entitled that defines how a 3.1 kHz audio signal is encoded at 32 kbps using Adaptive Differential Pulse Code Modulation (ADPCM).

G.722 - An ITU-T Recommendation that defines how a 7.5 kHz audio signal is encoded at a data rate of 64 kbps.

G.723 - An ITU-T Recommendation entitled, "Dual Rate Speech Coder for Multimedia Communication Transmitting at 5.3 and 6.4 kbps". G.723 is part of the H.323 and H.324 families.

G.728 - An ITU-T Recommendation for audio encoding using Low Delay Code Excited Linear Prediction (CELP). The bandwidth of the analogue audio signal is 3.4 kHz whereas after coding and compression the digitised signal requires a bandwidth of16 kbps.

G.729 - Part of the ITU-T's H.323 standard for videoconferencing over non quality-of-service guaranteed LANs.

Gateway - The gateway allows LAN-based H.323 systems to interoperated with other H.32x products. For instance, the gateway could link the H.323 session with an H.320 (ISDN-based) system; an H.321 (ATM-based) system; an H.322 (isoEthernet-based) system; or an H.324 (POTS-based) system. At the present, most H.323 gate-way implementations are concerned with linking H.323 and H.320 systems across a LAN/WAN connection.

GateKeeper - A gatekeeper is a utility that controls videoconference access on a packet-switched LAN. It requires that mul-timedia terminals register "at the gate", which is accomplished when the terminal provides its IP or IPX ad-dress. The gatekeeper translates network addresses and aliases to make connections. It can also deny ac-cess or limit the number of simultaneous connections to prevent congestion.

GHz - The gigahertz, abbreviated GHz, is a unit of alternating current (AC) or electromagnetic (EM) wave frequency equal to one thousand million hertz (1,000,000,000 Hz). The gigahertz is used as an indicator of the fre-quency of ultra-high-frequency (UHF) and microwave EM signals and also, in some computers, to express microprocessor clock speed. Other commonly-used units of frequency are the kHz, equal to 1,000 Hz or 0.000001 GHz, and the MHz, equal to 1,000,000 Hz or 0.001 GHz.

GroupWare - A term of software that runs on a LAN and allows co-workers to work collaboratively and concurrently. GroupWare is now being enhanced with video capabilities and many of the new desktop conferencing prod-ucts offer capabilities commonly associated with