Virtual Conferencing Glossary

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D-Channel - An ISDN channel that provides a 16-kbps or 64-kbps packet-mode connection between a servicing switch and a customer's premises. The channel carries signal and control information for B-channel activity and also can carry user data in the form of packets.

Data conferencing - A type of conferencing in an H.320 environment where conferencing systems transmit ITU-T T.120 informa-tion-for example, a PC file-for interactive use by conference participants.

DCE - Data Circuit-Terminating Equipment. A term that refers to the network side of a communication link.

Delay - The time it takes for a signal to go from the sending station through the videoconference to the receiving sta-tion. This transmission delay for a single hop videoconference connection is very close to one-quarter of a second.

Demodulator - A videoconference receiver circuit which extracts or "demodulates" the "wanted" signals from the received carrier.

De-Multiplex - The process of separating two or more signals previously combined for transmission over a shared channel. Multiplexing merges multiple channels onto one channel prior to transmission; de-multiplexing separates them again at an appropriate network node.

Desktop video conferencing - Videoconferencing that is conducted on a users personal computer. Most appropriate for small groups or individuals. Many desktop videoconferencing systems support document sharing.

Digital hierarchy (DS0, DS1) - A system of standardised transmission rate for digital signals using time-division multiplexing techniques. The rates are: DS0, 64 kbps (one voice channel), DS1, 1.544 Mbps (24 voice channels) DS1C, 3.152 Mbps (48 voice channels) DS2, 6.312 Mbps (96 voice channels) , DS3, 44.736 Mbps (672 voice channels) DS4NA, 139.264 Mbps (2,016 voice channels)

Digital signal - A way of sending voice, video, or data that reconstructs the signals using binary codes (1s and 0s) for transmission through wire, fibre optic cable, videoconference, or over air techniques. Digital audio/video sig-nals represented by discrete variations (in voltage, frequency, amplitude, location, etc.) can be transmitted faster and more accurately than analog signals.

Distance learning - The incorporation of video and audio technologies into the educational process so that students can attend classes and training sessions in a location distant from that where the course is being presented. Distance learning systems are usually interactive and are becoming a highly valuable tool in delivering of training and education to widely dispersed students in remote locations or in instances where the instructor cannot travel to the student's site.

Document sharing - A feature supported by many videoconferencing systems that allows participants of a videoconference to view and edit the same computer document.

DTE (Data Terminal Equipment) - As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, such as a videoconference terminal, LAN bridge or router.