Glossary - D
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D Channel - An ISDN Data channel is a data connection between the telephone company’s switching equipment and their customer’s ISDN equipment. It carries telephone connection information - signals to tell your equipment that a call is coming in and carry dialing and call handling information to the phone company’s equipment - and can also be used to carry multiple low-speed data connections using the X.25 packet-switching protocol.
Dark fiber - Unused fiber-optic cable that has been deployed but does not have the proper electronic and optical equipment to carry optical (light) signals. Generally considered to be extra fiber that will support future demand for communications capacity.
Data Communication - The movement of encoded information by means of electrical transmission systems. The transmission of data from one point to another over communication channels.
Data Compression - A technique that saves storage space by eliminating gaps, empty fields, redundancies, or unnecessary data to shorten the length of records or blocks.
Data Over Cable Service Interface Specifications (DOCSIS) - Specification for transmission of data over a cable network that has been approved by the ITU as an international standard. DOCSIS was developed by CableLabs and a consortium of North American multi-system cable operators.
Decibel (dB) - A unit to measure the relative levels of current, voltage or power.
Delay - The elapsed time between the instant when user information is submitted to the network and when it is received by the user at the other end.
Delay Distortion - Distortion resulting from non-uniform speed of transmission of the various frequency components of a signal; i.e., the various frequency components of the signal have different times of travel (delay) between the input and the output of a circuit.
Delay spread - An effect of multi-path for a digital interface in which multiple reflections of the same signal arrive at the receiver at different times, creating a noticeable degradation in signal quality.
Demographics - Breakdown of television viewers by such factors as age, sex, income levels, education and race.
Demodulation - The extraction of the modulation or information from a radio-frequency current.
Dense Wave Division Multiplexing (DWDM) - A technology that provides in fiber the equivalent of frequency division multiplexing, in metallic wire. Separate parallel channels are transmitted on a single fiber, with one wavelength for each channel. Current products enable 16 channels of 2.5Gb each for a total of 50Gb per fiber. DWDM can operate over existing single-mode fiber, and therefore reduce upgrade costs.
Descrambler - An electronic circuit that restores a scrambled video signal to its standard form.
Dial-up - Data communication established by a circuit-switched connection over a telephone network. Generally associated with less than broadband speeds (56 kbps or less).
Digital - (1) In communications and computer technology, digital refers to a method of encoding information using a binary system made up of zeroes and ones. In communications technology this takes the form of two very different electrical voltages, several volts positive and negative, to represent the two values. This substantial difference in voltages for each state makes it unlikely that minor fluctuations in voltage due to electro-magnetic interference will change the way a signal is interpreted when received. (2) Information that is encoded into bits and bytes, or packets (0s and 1s, computer binary language). Generally perceived to be an advanced communication form offering clearer signals and increased transmission capacity.
Digital Application Software Environment (DASE) - A standard by ATSC addressing interactive television.
Digital Audio Visual Council (DAVIC) - DAVIC is an international consortium working on the development of standards for interactive television.
Digital Compression - An engineering technique for converting a cable TV signal into a digital format which may then be processed in a manner that requires a smaller portion of spectrum for its transmission. This compressed format allows many channels to be carried in the bandwidth normally required for one signal. This format can also be easily stored and manipulated.
Digital Enhanced Cordless Telecommunications (DECT) - A European standard governing panEuropean digital mobile telephony. Specified in DVB MHP as a type of return channel network interface for use in receiving and transmitting IP packets.
Digital Facility - A switching or transmission facility designed specifically to handle digital signals.
Digital Set-Top Box - A device which accepts digital encoded television broadcasts and converts them to display on an analog television set.
Digital Signal - A signal that has a limited number of discrete states prior to transmission. This may be contrasted with an analog signal which varies in a continuous manner and may be said to have an infinite number of states.
Digital subscriber line (DSL) - High-speed technology to transfer data over an existing twisted-pair copper telephone line. Asynchronous technology (ADSL) provides data transmission rates up to 7 Mbps in one direction, generally within approximately three miles from a telephone central office. See also HDSL and VDSL.
Digital Subscriber Line Access Multiplexer (DSLAM) - A DSLAM is an xDSL line-interface device located in a telephone company Central Office. One side of a DSLAM connects to customer premises network interface devices (NIDs) over the local loop. The other side interfaces with the PSTNand a wide area (Frame Relay or ATM) network system.
Digital Transmission - A mode of transmission in which all information to be transmitted is first converted to digital form and then transmitted as a serial stream of pulses. Any signal-voice, data, television-can be converted to digital form.
Digital Video Broadcasting (DVB) - Digital video broadcasting is a European standard for digital television.
Digital Video Recorder (DVR) - A consumer device which uses a hard disk drive to record television programs. Also provides pause of live television feature. See PVR.
Digital Video Subcommittee (DVS) - An ANSI-sponsored standardization committee of the SCTE.
Direct broadcast satellite (DBS) . Satellite technology that transmits directly to the end user or customer. DBS describes a frequency allocation and wide spacing between satellites that generally permits higher-powered transmissions through the air to small 18- to 24-inch receiving facilities located on customer premises (“point-to-multipoint” transport). Also known as direct-to-home (DTH) satellite.
Directional Coupler - A high-quality tapping device providing isolation between tap and output terminals.
Directive Transmission - Directionally focused signal transmission from a base station to a remote user made possible by certain smart antenna systems with digital signal processing capabilities; these base stations use information obtained during reception to transmit signals selectively toward certain users and away from others.
Dish Antenna - A high-grain antenna, shaped like a dish, that is used for the transmission and reception of ultra-high-frequency and microwave signals.
Disk Operating System (DOS) - The basic term for software which controls a computer’s operation and is loaded from some form of disk, usually a hard drive.
Distant Signal - Broadcast TV signals which originate at a point too far away to be picked up by ordinary home reception equipment; also signals defined by the FCC as outside a broadcaster’s license area. Cable systems are limited by FCC rules in the number of distant signals they can offer subscribers.
Distortion - The departure, during transmission and amplification, of the received signal wave form from that of the original transmitted wave form.
Distribution Hub - A location in a cable television network which performs the functions of a headend for customers in its immediate area, and which receives some or all of its television program material from a master headend in the same metropolitan or regional area.
Distribution Plant - The hardware of a cable system—amplifiers, trunk cable and feeder lines, attached to utility poles or fed through underground conduits like telephone and electric wires.
Distribution System - The part of a cable television system used to carry signals from the headend to subscriber’s receivers. Often applied, more narrowly, to the part of a cable television system starting at the bridger amplifiers.
DOCSIS Radio Frequency Interface (RFI) Specification - CableLabs radio-frequency interface specifications for high-speed data-over-cable systems.
Domain Name Server (DNS) - A server that relates an internet domain name (such as www.cablelabs.com) to an IP address.
Double-Click - Two rapid clicks of the primary (usually left) mouse button, usually performed to launch a program or open a file.
Downlink - Transmission of signals from a satellite to a dish or earth station.
Download - The transfer of data from a remote computer, or server, to a local computer. To the Internet user, downloading means to request a copy of a file from another computer and then receive that file.
Downstream - Flow of signals from the cable system control center through the distribution network to the customer. For communication purposes, associated with transmission (down) to the end-user. Or in cable television, the direction of transmission from the headend to the subscriber.
Drop - The cable and hardware from tap to subscriber is called the drop.
Drop Cable - Generally 330 feet or less, of coaxial cable, starting at a tap and continuing on to the subscribers connection. Or coaxial cable that connects to a residence or service location from a directional coupler (tap) on the nearest coaxial feeder cable.
Dual Cable - Two independent distribution systems operating side by side, providing double the channel capacity of a single cable.
Dual Tone Multi Frequency (DTMF) - Telephone “touch” tones. So-called because each keypad button pressed generates a unique combination of two audible tones or frequencies.
Duplex - In a communications channel, the ability to transmit in both directions.
Dynamic Host Configuration Protocol (DHCP) - An Internet protocol used for assigning network layer (Internet Protocol) addresses. Or the DHCP is an Internet standard for assigning IP addresses dynamically to IP hosts.
Dynamic Range - The ratio between the greatest signal power that can be transmitted over a multichannel analog transmission system without exceeding distortion or other performance limits, and the least signal power that can be utilized without exceeding noise, error rate or other performance limits.
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