311GlossaryG.729Audio encoding/decoding formatrecommended by the ITU-T. A phonebandwidth audio signal is converted to adigital signal with the data rate of 8 Kbps.GatekeeperControls the access of H.323videoconference devices on a network.Administers the zone, access limitation,audio/video bandwidth, and alias etc.H.221Frame structure for a 64 to 1920 Kbpschannel in audiovisual teleservices.H.239ITU-T standard for sharing data andpresentations with video. This supports thedual video presentation mode, enablingendpoints to receive and transmit video andpresentation data simultaneously.H.261Video codec for audio/visual services as p ×64 Kbps. Videoconferencing standard thatdefines a video coding algorithm, pictureformat and error correcting technology forcommunication between differentmanufacturers’ video codecs.H.263A video coding algorithm based on theH.261 standard. This format enablescommunication via a lower bit rate.H.263+Video encoding/decoding format based onthe H.263 standard, added by the Annex I toT (I, J, K …… T), that allows enhancedpicture quality and error resistance.Normally, this format is a profile used witha combination of some of the Annex forH.263/H.263+.H.264A video coding algorithm newlystandardized by the ITU-T in May 2003.This format realizes high-quality picture viaa lower bit rate. It provides an equal picturequality via half as low bit rate as the H.263format. The H.264 format is also called asMPEG4 Advanced Video Coding (AVC).H.320A videoconferencing standard forcommunication between differentvideoconferencing system.H.323This enables communications on the non-QOS (Quality of Service) LAN.HMLPSee “MLP”.I-MUXAn abbreviation for Inverse Multiplexer.This protocol allows you to transmit the dataat 384 Kbps via 6B-channel.Interlaced SIFWith TV pictures, 60 fields of pictures persecond are interlaced to provide highresolution and smooth motion pictures.The conventional videoconferencing systemuses CIF format pictures (352 pixel × 388line) transmitted in 30 fields per second. InCIF format, smooth motion pictures like TVpictures cannot be obtained. In the InterlacedSIF format, interlaced SIF size pictures (352pixel × 240 line) can be transmitted at 60frames per second. This enables display ofpictures with higher vertical resolution of352 pixel × 480 lines, providing smoothmotion picture. However, a relatively higherbit rate is required as the amount ofinformation is twice as much as that of theCIF format.ISDNAn abbreviation for Integrated ServicesDigital Network. This is a communicationprotocol by CCITT on transmission ofintegrated voice, video, and data.Bandwidths include basic (64 Kbps) andprimary rate (1.544 and 2.048 Mbps).ITU-TAn abbreviation for InternationalTelecommunication Union,Telecommunications.
