To use the glossary, simply click below on the first letter of the term of interest:

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

D4

A T1-transmission framing and synchronization method, consisting of a series of digital 1's and 0's in a unique order, each member of the series being sequentially inserted in a T1 stream after every 193 data bits. See also B8ZS.

DAB

Digital Audio Broadcast, digital audio signal added to a conventional FM broadcast signal following FM modulation. Compatible with standard FM radio broadcast receivers, a special decoder is needed to hear the DAB signal.

DACS

Digital Access Cross-connect System (which see). Included as part of public and private conventional digital networks, a DACS may commonly switch DS3, DS1 and DS0 and other high level digital signals and is useful for configuring complex networks. A DACS is not a substitute for an MCU.

dB

Decibel. One-tenth of a Bell, a logarithmic measurement of acoustic, electromagnetic or electrical power, voltage or current ratios.

DBS

Direct Broadcast Satellite, C- and Ku-band satellite services providing television, sound, video and data signals directly to home users. The signals are often encrypted, intended for reception by subscribers, requiring an IRD for reception.

DCE

A configuration protocol identifying Data Communication Equipment, the type of data connection at equipment that connects to a communications facility. This consideration is important when interconnecting RS-449, RS-232, V.35, X.21 and other similar digital communications signals. Compare DTE.

 

Distributed Computing Environment, a complex middleware platform providing security services.

DCR

Degradation Category Rating, an ITU-T P.800 subjective testing protocol, similar to CCR but is based on the test subject always listening first to the reference signal followed by the signal passed through the device under test, a test performed by HEI.

DCT (Discrete Cosine Transform)

see Cosine Transform.

DECT

Digitally Enhanced Cordless Telephone, operates in the 1880-GHz - 1900-GHz band using Bluetooth's GFSK (MC/TDMA/TDD) technology.

DES

Data Encryption Standard. A 64-bit private-key encryption technique developed by the US NBS. An encryption system that encodes communications, providing security and "privacy" of communication by making interception and decoding impossible (for most practical purposes). Double DES or DES2 uses tandem DES algorithms for greater security. Variants may use variable-length keys.

DLCI

Data Link Connection Identifiers (frame-relay use)

Digital Access Cross-connect System (DACS)

A network central office device which enables any T1 facility or any of a T1's 24 channels to be switched or cross-connected to one or more T1 (DS1), DS3 or other high-order facilities.

Digital Signal

Signal represented by a sequence of binary bits representing ones and zeros.

Differential Interframe Coding

In motion video compression, the transmission of only the difference information between adjacent video frames.

Diversity (transmission use)

In telecommunications, reliability may be improved by use of various forms of diversity within a system. Techniques may include time, space, frequency, route, path or other forms of diversity. In addition, redundant equipment, power and other systems can further increase reliability. Different degrees of availability (or reliability) may be achieved depending upon the nature of the diversity used.

DMOS

Degradation Mean Opinion Score, an ITU-T P.800 subjective listening test where the test subjects compare two signals, first the reference, then the signal passed through the device under test.

DNS

Domain Name System, an automatic Internet phone book, translating an easy-to-remember domain name like hei.ca to its Internet address like 69.6.238.89 and vice-versa.

Dolby Digital 5.1

Formerly known as AC-3, Dolby Digital^® provides efficient encoding and noise reduction for high-quality surround sound™ applications including home entertainment, theatre and broadcasting, including DBS and DVD source material. Dolby Digital requires appreciable bandwidth, 448 Kbps being typical, a reason why it is not available for all material provided by direct broadcast satellite.

DPCM

Differential Pulse Code Modulation. A digital coding and compression process in which the analog signal is first sampled, and the difference between each sample of the signal and its prior estimated value is quantized and digitally encoded.

DS0

The AT&T Bell System level 0 digital standard for systems operating at 64-Kbps.

DS1

The AT&T Bell System level 1 digital standard for systems operating at 1.544 Mbps and consisting of 24 DS-0 channels.

DS3

The AT&T Bell System level 3 digital standard for systems operating at 44.736 (45) Mbps.

DSL

Digital Subscriber Line, a generic term encompassing a family of moderate speed access using a subscriber's existing copper lines.

DSLAM

Digital Subscriber Line Access Multiplexer, a central office device which terminates all the customer xDSL lines.

DSP

Digital Signal Processor, an often massively parallel microprocessor optimized for high efficiency processing of telecommunications signals.

DSU

Digital Service Unit, see CSU.

DSX-1

Digital Signal Cross-connect level 1, a DS0 or T1 switch and interface specification.

DTE

A configuration protocol that identifies Data Terminal Equipment; the type of data communications connection at equipment connecting to a DTE device, compare DCE.

DTH

Direct-To Home. Simplex satellite broadcast services like DirecTV, Echostar and ExpressVu, transmitting directly to end-users. Similarly, MMDS or wireless cable can provide service from a fixed terrestrial transmitter site often including a return data or audio path. No wired system is needed, making these technologies ideal for sparsely populated areas.

DTMF

Dual-Tone Multi-Frequency, the method of telephony signaling used by all modern telephones, modems and similar equipment.

Dual Communications Interface

An interface that allows simultaneous transmission of two halves of a set of communications data over two similar communication interfaces. A familiar example is ISDN-BRI (2B+D), a connection using two switched 56- or 64- Kbps transmission circuits. See also H.244.

Disclaimer and Copyright © 1996-2010 HEI