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Term Description D (Delta) Channel A 16 Kbps (for BRI) or 64 Kbps (for PRI) packet switched channel used for signaling and data. Daisy chain Multiple devices that are connected in series. The output of the first device is connected to the input of the next device. Data link layer The OSI level that performs the assembly and transmission of data packets (gets data packets on and off the wire), does error detection and correction, synchronization and retransmission. It includes the Medium Access Control (MAC) & Logical Link Control (LLC). The LLC on the upper half, which does the error checking The MAC on the lower half, which deals with getting the data on and off the wire. The primary purpose of the Data Link Layer is to provide error-free transmission of information between two end stations "edge nodes" attached to the same physical cable or media. This then allows the next higher layer to assume virtually error-free transmission over the physical link. The Data Link Layer is responsible for packaging and placing data on the network media. It then manages how the flow process of the bit stream takes place. Data Width Total number of bits/bytes of data that can be accessed (read or written) simultaneously. DAVIC Digital Audio Video Council. An international group which met for the first time in 1994, is set up to define the interfaces and protocols necessary to support delivery of international digital video services.   dB Decibel. A logarithmic representation of magnitude relationships commonly used in radio and sound measurement.   DBS Direct Broadcasting Satellite (TV). It is an American transmission system based on high powered Ku-band satellites (120-200 watts per transponder). The signals can be received using a small 18 inch dish. Currently there are four DBS-Services in peration in the US (Primestar, DirecTV/USSB and EchoStar).   DBS Direct-broadcast satellite (TV).   DCF Distributed Coordination Function   DCM (HAVi) Device Control Modules. A Device Control Module (DCM) is a Software Element that is installed and executed on a HAVi device that provides control over device-specific functionality, (such as a VCR or a camera) via the HAVi-defined APIs (such as the "PLAY" API of a VCR). DCMs are installable Software Elements, which means that their presence depends on which devices or functionality is actually present in a particular HAVi network. In principle there can be multiple DCMs for one particular device present in a HAVi network. When a device is inserted or powered up in the network, all IAVs and FAVs will check to determine if they have a DCM for that device, and will then negotiate with each other as to which DCM will be installed for the device, and on which IAV or FAV it will be installed. Only one DCM can be installed at any time for each particular device. This selection and installation process is controlled by the DCMs on the IAVs and FAVs, however, HAVi offers several user definable preferences setting. DCT Discrete Cosine Transform. This is the Cosine of the infinite Fourier series. DDR Double Data Rate. This memory transfers data on both edges of the clock. DDR RAM Acronym for Dual Data Rate. Type of RAM that runs twice as fast as traditional RAMs. DDR RAM is written to, or read from on both clock edges. Decoder A device that restores a signal to its original form after it has been encoded. It is the block responsible for stripping the extra bits appended by the Encoder to the digital data. Decoding A process in which the original coded information is reconstructed. Decryption A procedure to convert ciphertext back into plaintext. DECT Digital Enhanced Cordless Telecommunications Delta Modulation (DM) A variant of pulse code modulation whereby a code representing the difference between the amplitude of a sample and the amplitude of the previous one is sent. Operates well in the presence of noise, but requires a wide frequency band. Demodulate To convert a modulated signal back to an unmodulated "baseband" signal. Demodulation Opposite of modulation; the process of retrieving data from a modulated carrier wave. Conversion of analog carrier signal to digital information. Demodulator A device that extracts digital information from transmitted carrier waves. DES The Data Encryption Standard. An encryption standard issued by the National Bureau of Standards, it was adopted by the US government in 1977, as the federal standard for the encryption of commercial and sensitive-yet-unclassified government computer data and is defined in FIPS 46 (1977). The DES is the algorithm in which a 64-bit block of plaintext is transformed (encrypted/enciphered) into a 64-bit ciphertext under the control of a 56-bit internal key, by means of permutation and substitution. Design Reuse Establishing proven designs into intellectual property (IP) for use in future designs. De-spreading The process used by a correlator to recover narrowband information from a spread spectrum signal. Developer The mechanism and magnetic powder used to transfer toner from the toner hopper onto the photoreceptor. DFF Acronym for Data Flip Flop. A basic logic function that stores the input value of a signal when triggered by the clock input. DFPQ Distributed fair priority queuing DHCP Dynamic Host Configuration Protocol. A TCP/IP protocol that enables a network connected to the Internet to assign a temporary IP address to a host automatically when the host connects to the network. Dial Tone A tone indicating that automatic switching equipment is ready to receive signals. Diffuse Dither A method for printing continuous-tone images on laser printers in which the grayscale information is represented by randomly located printer dots. Diffuse dithers do not photocopy well because of the small, random, dot location in the image. Digital Certificates A virtual security document which ensures the association between the user's public key and the user's identity and security privileges. Digital Compression A way of reducing the number of bits in a digital signal by using mathematical algorithms to eliminate redundant information, thereby reducing the space the signal occupies when being transmitted or recorded. Digital modem A system component which allows modem users to communicate over digital access/communications channels. They work by converting the PCM-encoded digital data streams sent by analogue modem users into their original analogue waveform. Digital signal A signal that is composed of two energy levels (on (1) and off (0)). Digital signals are used by computers to transmit data. The pattern of the level changes represents individual bits of information. Digital Signature A method of signing electronic documents using public key encryption that certifies that the document was originated or "signed" by a specific person or organization. It can also be used to verify the integrity of the document. Direct Form A filter implementation that only has delays, summations and multiplication but no feedback Dish The dish collects, reflects and focuses the satellite signal into the LNB. Distributed Arithmetic A method which breaks down DSP algorithms to its basic components of ANDs and ORs, allowing from serial to fully parallel realizations in the Xilinx FPGA architecture. Distributed RAM Xilinx term for implementation of RAM within a CLB. Dithering A halftoning method where several dots of the primary colors are printed in various patterns to give the impression of a larger color spectrum. DLC Digital Loop Carrier. Equipment located in street-side cabinets or on telephone poles that collects copper telephone circuits onto a fiber optic connection to the CO. Some DLCs are able to support DSL lines for ILEC. CLECs cannot (usually) deploy DSL to customers hosted on DLCs. DLL Acronym for Delay Locked Loop. A digital circuit used to perform clock management functions on and off-chip. DLP Digital light processor DMA Acronym for Direct Memory Access. Logic function that allows the memory to be accessed directly by a peripheral. DMT Discrete Multi-Tone. Modulation scheme in which available bandwidth is divided into sub-channels (256 for downstream), maximizing the use of the clearer channels.Recently selected by ANSI and ETSI over CAP for ADSL standard. DMT is a form of Frequency Division Multiplexing. DNS Domain Name System - The distributed name/address mechanism used in the Internet. The DNS is used for mapping host names onto their network addresses. DOCSIS Data Over Cable Service Interface Specification. The dominating cable modem spec that defines the technical specs for both the cable modem and the CMTS. Dot A single point written by a laser, or a single point in a bitmap. Dot Matrix A type of printer, also known as serial dot matrix, that uses one or two columns of dot hammers to form images out of dots. The more dot hammers used, the higher the resolution of the printed image. Doubleword 32 bits, most often known as "DWORD". Down-converter A device that reduces the high frequency signal to a lower, intermediate range. There are three types of down-conversion: signal, dual and block. Downlink Term used to describe the re-transmitting of signals from a satellite, back to Earth. Download The download function enables service providers to update the system software of their Set-top Boxes via their transmission channels. Download Audio Downloading, which involves transferring the entire file to your computer before any part of it is accessible, offers better quality since the data rate of the compressed stream does not have to less than the data rate of the Internet connection. MP3 audio for example, is targeted at data rates from 64 to 128 Kbps The goal of these formats is to provide near CD quality audio. Downloaded Font A font which is stored in a computer, and sent to the printer via the communications interface when required, to be stored in the printer. Normally downloaded fonts are held in RAM on the printer, and are lost when the printer is switched off. Some printers are able to hold downloaded fonts on hard disk to prevent loss when the printer is switched off. Downstream Data received by the modem from the Internet DPI Dots Per Inch: a unit of measure used to describe the resolution of images produced by printers or other output devices. The printed dots from a 600 dpi printer are far smaller than the dots created by a 300 dpi printer. As a result, the output is smoother and more detailed, while dithering patterns will deliver more realistic colors. DPSK Differential Phase Shift Keying. A simplified BPSK where only data transitions are transmitted. DRAM Dynamic Random Access Memory. Memory that consists of small capacitors for each bit of memory. Since capacitors do not hold a charge indefinitely, DRAM must be constantly refreshed to avoid losing its contents. Also, the process of reading the contents of the memory are destructive, meaning extra time must be spent restoring the contents of memory addresses which are accessed, so DRAM is slower than SDRAM. DRAM Acronym for Dynamic Random Access Memory. Type of memory where any location may be read from or written to. Data needs to be continually refreshed. Drum A common term for a cylindrical photoreceptor. DSL Digital Subscriber Line. Local digital network loop, typically sends high-speed data over standard phone lines. A family of related "broadband over phone wire" technologies, used to provide a continuous, high-speed connection directly to an Internet Service Provider (ISP). It refers to the variety of different types of Digital Subscriber Line protocols - high-speed data transmission protocols that are compatible with regular copper telephone wire. DSL modem A type of modem that connects a computer to a DSL network, which in turn connects to the Internet providing users with a continuous, high-speed connection to the Internet DSLAM Digital Subscriber Local Access Multiplexer. This aggregates multiple DSL connections onto fiber and delivers them to an Access Switch. Takes many ADSL lines (ATU-C units) and concentrates them, typically to a single ATM line, typically at the CO. DSP Digital Signal Processor. A specialized microprocessor which contains hardware features specifically tailored to the processing of signals and hence provides flexible processing of a continuous stream of information. DSS Digital Satellite System DSSS Direct Sequence Spread Spectrum. A spread spectrum technique where a pseudo-random code directly phase modulates a carrier, and hence spreads its signal continuously over a wide frequency band. DSSS generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To the receiver, DSSS appears as low-power wideband noise spectrum and is rejected (ignored) by most narrowband receivers. The signal is despread by correlating with a pseudo-random code identical to and in synchronization with the code used to spread the carrier at the transmitter. This modulation technique increases the bandwidth of the transmission. DSTB Digital Set-top Box DTH Direct-To-Home. Used to denote satellite TV signals received by a household via an individual dish installation. DTV Digital television. Dual port RAM RAM with two independent ports, each capable of being read and/or written simultaneously and independent of the other port. Xilinx refers to this functionality as True DualPort RAMTM. Dual Tone Multi-Frequency (DTMF) Also known as touch-tone. A type of signaling which emits two distinct frequencies for each indicated digit. DVB Digital Video Broadcasting. This group was created to establish a technical framework for the introduction of digital broadcasting systems to suit the whole range of delivery mechanisms, including cable, satellite, terrestrial and MMDS. DVB has already developed a coherent set of methods to bring digital television to home. DVB-C Signals via Cable. DVB-S Signals via Satellite. DVB-T Signals via Terrestrial. D-VCR Digital VCR DVD Digital Video / Versatile Disk. DVD Technology provides storage capacity that is about 6-7 times greater than that of CD technology with the same aerial space. It provides multiple languages on movies, with multiple language subtitles. A beam of laser light touches the disc and data portion of a DVD disc is never touched by a mechanical part when played eliminating wear characteristics on the disc. The superior audio and video quality, interactivity and distribution control incorporated in this new medium has revolutionized video distribution. It takes advantage of MPEG-2 technology. DVD-A Digital Video Disk - Audio. It is a new DVD format providing multi-channel audio in a loss-less format. It is being positioned as a replacement for the CD. DVI Digital Video Interface DVR Digital Video Recorder. It is a product that uses local storage to enable the user controlled storage and playback of live digital video streams on a real-time basis. The functionality includes the ability to simultaneous record & playback of separate video streams or different portions of the same stream in real time. Dye-Sublimation A specialist print technology used for demanding graphic arts and photographic applications that require continuous tone output. Dynamic Current It is the amount of current the device needs when it is active. The dynamic current is mainly due to switching of internal nodes, loading on the outputs and external clocks. Dynamic detection, auto sense The process by which a system can detect that a new device has been added or removed from the PC. This process allows the operating system and applications to immediately begin using the added devices or stop using the removed devices without rebooting the system.   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