Virtual Conferencing Glossary

H

H0 - In the ISDN, a channel that provides a 384-kbps connection, or the equivalent six B channels, via a switched or non-switched portion of a network.

H11 - In the ISDN, a channel that provides a 1.536-Mbps (equivalent to T1) connection via a switched or non-switched portion of a network. The connection operates at the equivalent 24 B channels.

H12 - In the ISDN, a channel that provides a 2.048-Mbps (equivalent to E1) connection via a switched or non-switched portion of a network. The connection operates at the equivalent 30 B channels.

H21 - In the ISDN, a channel that provides a 32 Mbps connection via a switched or nonswitched portion of a net-work. The connection operates at the equivalent 512 B channels.

H.221 - A framing portion of the ITU-T's H.320 Recommendation that is formally known as "Frame Structure for a 64 to 1920 kbps Channel in Audiovisual Teleservices". The Recommendations specifies synchronous operation in which the coder and decoder synchronise timing.

H.222 - ITU-T Recommendation specifies generic coding of moving pictures and associated audio information.

H.223 - Part of the ITU-T's H.324 standard specifying a control/multiplexing protocol, which is formally called "Multi-plexing protocol for low bit rate multimedia communication".

H.230 - A multiplexing Recommendation that is part of the ITU-T family of video interoperability Recommendations. The recommendation specifies how individual frames of audiovisual information are to be multiplexed onto a digital channel.

H.231 - A Recommendation added to the ITU-T's H.320 family specifying multipoint control unit used to bridge three or more H.320 compliant codecs together in a multipoint conference.

H.242 - Part of the ITU-T's H.320 family of video interoperability Recommendations. H.242 specifying the protocol for establishing an audio session and taking it down after the communication has terminated.

H.243 - Enables you to browse other videoconference sites manually or take control of the conference and select the default broadcaster. Not all systems support this feature.

H.245 - Part of the ITU-T's H.324 family defining control of communications between multimedia terminals.

H.261 - The ITU-T's Recommendations that allows dissimilar video codecs to interpret how a signal has been en-coded and compressed, and to decode and decompress that signal. It also defines two picture formats: CIF and QCIF.

H.263 - A new standard that has better motion handling at lower bandwidth than H.261. All sites must be capable of supporting this standard to use this option.

H.320 - An ITU-T standard including a number of individual recommendations for coding, framing, signalling and establishing connections (H.221, H.230, H.321, H.242, and H.261). It applies to point-to-point and multipoint videoconferencing sessions and includes three audio algorithms, G.721, G.722 and G.728.

H.323 - The H.323 extends the H.320 to IP networks or Internet over LANs: Ethernet, Token-Ring, and other packet-switched networks that do not guarantee QoS. It will support both point-to-point and multipoint operations.

H.324 - An ITU-T standard that provides point-to-point video and audio compression over analogue telephone lines (POTS). It can incorporate H.261 video encoding, but most implementations will probably use H.263, a scal-able version of H.261 that adds a 128-by-96 Sub-QCIF (SQCIF) format. Because of H.263's efficient design, it may produce frame rates much like those of today's ISDN H.320 systems through inexpensive hardware-assisted modems. The H.324 family includes H.223, a multiplexing protocol. H.245, a control protocol, T.120, a suite of audiographics protocols and V.34, a modem specification.

Half duplex audio - 2-way audio transmitted and received in turn (rather than simultaneously) so only one site can speak at a time. Contrast with full duplex audio.

HDLC - High-Level Data Link Control. Bit-oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame charac-ters and checksums. See also SDLC.

HMLP - High-speed multi layer protocol. Standard for high speed data transmission. T.120 systems use this for high-speed transfer. HMLP channels are multiples of 64 kbps.

Homologation - Conformity of a product or specification to international standards, such as ITU-T, CSA, TUV, UL, or VCCI. Enables portability across company and international boundaries.

HSD - High Speed Data, in ISDN it is the transmission of Video, Audio and Data in multiples of 64 Kbps.

Hub - A network's or systems signal distribution point where multiple circuits convene and are connected. Some type of switching or information transfer can then take place. Switching hubs can also be used in Ethernet LAN environments which is an arrangement whereby a LAN segment might support only one workstation. This relieves congestion through a process called micro-segmenting.