ctrical pressure caused by electrons repelling other electrons. Very Small Aperture Terminals. Small transportable satellite earth stations used in videoconferencing BTV applications. VTS 1.5 Compression Lab's first codec that was introduced in Video Communication: the Whole Picture 1982. It had an operating bandwidth requirement of 1.544 Mbps (T-1), remarkable for the time. watts A measure of the power or electrical energy of a signal or waveform. wavelength division A technology that uses lasers to transmit multiple light multiplexing signals concurrently over a single optical fiber. With WDM, each signal travels within its own color band and is modulated by transmitted data. waveform A presentation of the varying amplitude of a signal in relation to time. See Wavelength Division Multiplexing white balance A camera feature that adjusts the balance between the RGB components that yields white in the video signal. Cool-temperature lighting casts a different tint on a room than does warm-temperature lighting. White balance produces a uniform white regardless of room lighting. white noise Noise, containing energy, distributed uniformly over the frequency spectrum. whiteboarding The ability for multiple users to share a drawing space, generally a bit-mapped image that all conferees can modify. wide area network WAN, a collection of circuits that make up the public switched network and over which organizations communicate. Used primarily in Europe, X.21 is a standard that operates at bit rates between 56 Kbps and 384 Kbps to control network dialing. A valuable feature of X.21 is its inherent dialing functions, including the provision for reporting why a call did not complete. X.21 can be used to connect to both switched and dedicated networks. Glossary of Terms The common nomenclature for the luminance signal. In component video, the Y or luminance signal is kept separate from the C (hue and color saturation signal) to allow greater control and to enable enhanced quality images. The luminance is recorded at a higher 