The Cable Center

This glossary of cable and telecommunications terms is intended to enhance your understanding of this dynamic industry. We are able to present this information with the generous help of CableLabs - consult their website for the most up-to-date information about cable technology.

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Value-Added Reseller (VAR)
Refers to distributors that also provide other services such as systems integration or network management.

Variable Bit Rate (VBR)
A type of telecommunications service characterized by a service bit rate specified by statistically expressed parameters that allow the bit rate to vary within defined limits.

VDSL
Very high-speed digital subscriber line that utilizes existing copper infrastructure of the telephone companies. VDSL offers video and data transmission rates up to 52 Mbps up to 2,700 feet. See also DSL.

Velocity of Propagation Velocity of signal transmission
In free space, electromagnetic waves travel with the speed of light. In coaxial cables, this speed is reduced. Commonly expressed as percentage of the speed in free space.

Vertical Blanking Interval (VBI)
A portion of the television signal that does not contain visual data. In NTSC, the VBI are lines 1 through 21 in each field.

Very High Frequency (VHF)
Channels 2-13 (54-88 MHz and 174-216 MHz)

Very Small Aperture Terminal (VSAT)
Small earth stations with a satellite dish usually 4-6 feet in diameter used to receive high speed data transmissions; can also transmit slow-speed data.

Vestigial Sideband Transmission
A system of transmission wherein the sideband on one side of the carrier is transmitted only in part.

Video
A term pertaining to the bandwidth and spectrum of the signal which results from television scanning and which is used to produce a picture.

Video Band
The frequency band utilized to transmit a composite video signal.

Video-on-Demand (VOD)
Allows the end-user subscriber to select at any time movies they wish to view from a large selection of titles and categories stored on a remote server. Service may also provide VCR functionality, (stop, pause, etc.) which allows the end-user subscriber to control the “play back” of the server from the remote control. Or a television service where viewers can select and watch video content for viewing at any time.

Video Transmission
The original video signal before it is modulated and converted to radio-frequency and broadcast or cablecast. A home television set reconverts radio-frequencies to a video signal.

Videotape
Used to electronically record sight and sound for instant playback. Videotape comes in half-inch, three-quarters, one and two-inch widths and can be erased and re-recorded.

Videotape Recorder (VTR)
A device which allows the recording and playback of magnetic tape sound and picture recordings.

Videotex
The generic term used to refer to a two-way interactive system for the delivery of computer-generated data into the home, usually using the television set as a display device. Some of the more often used specific terms are “viewdata” for telephone-based systems (narrowband interactive systems); “wideband broadcast” or “cabletext” for systems utilizing a full video channel for information transmission; and “wideband two-way teletext” for systems which could be implemented over two-way cable television systems. In addition, hybrids and other transmission technologies, such as satellite, could be used for delivery of videotex services on a national scale.

Viewers Per Viewing Household (VPVH)
A demographic percentage which indicates how many persons per 100 or per 1,000 households are viewing. For example, a VPVH of 80 K2-11 means that for every 100 households viewing, there are an estimated 80 children ages 2 to 11.

Violence Chip (V-Chip)
A term used to describe a microchip which will permit parental control over rated television programs.

Virtual Channel (VC)
The communication channel that provides for the sequential unidirectional transport of ATM cells.

Virtual Channel Table (VCT)
Data declared as part of the Service Information standard defined by SCTE.

Virtual circuit
This term refers to a predefined path through a network that provides a connection-oriented session between two applications.

Virtual Private Network (VPN)
A term that is applied to either voice or data networking. In essence, a VPN is a portion of a public network that has been logically partitioned for private use.

Voice Activation Detection (VAD)
Allows a data network carrying voice traffic to detect the absence of audio and conserve bandwidth by preventing the transmission of “silent packets” over the network. Most conversations include about 50% silence. VAD is also called “silence suppression”.

Voice-over-Internet Protocol (VoIP services)
These services are a provision of voice telephony via the use of packet-switched networks running Internet Protocol (IP) networks rather than traditional circuit switching. CableLabs has developed the PacketCable specifications for the delivery of IP-based multimedia services, including voice services, over the DOCSIS 1.1 access network.

Voice-Over-Net (VON)
A term that refers to various sets of technologies that are used to enable voice applications across the Internet.