D0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T | U-Z
0-A | B | C-Cn | Co-Cz | D | E | F-G | H-I | J-L | M | N-O | P-Q | R | S | T
- D4 Framing: A T1 12-frame
format in which the 193rd bit is used for framing & signal information; ESF is
an equivalent but newer 24-frame technology.
- Daisy Chain: To connect
together in a series.
- DAT: See Digital Audio
- Data: Information represented in digital form, including
voice, text, facsimile, & video.
- Data Communications: The reception,
transmission & validation of data. The transfer of data between a data source &
data link via one or more links.
- Data Communications
Equipment: A device that transfers data from one type of wire to another. A
Modem is a DCE device that transfers data from the wire or cable to the phone
line. Typically the wiring from a DTE to a DCE is
- Data Encryption Key: (DEK) Much like an
actual key used for locking & re-opening doors, DEKs are used for the
encryption & decoding of message text, sometimes in the form of a digital
- Data Integrity: A measure of accuracy based on error
- Data Link: Any serial data communications transmission
path, generally between two adjacent nodes or devices & without intermediate
- Data Link Control: The rules or
procedure for reliable data transfer between two communicating DTE's A DLC
makes specifications for Session Establishment, data Transfer, & error
- Data Link Layer: The network
protocol module (defined as level 2 by OSI) which defines how packets for a
specific type of LAN or network trunk line are addressed, structured, &
delimited. The Data Link Layer has an interface downward to the Physical Layer,
& upwards to the Network Layer.
- Data Service Unit:
(DSU) A component of customer premises equipment used to interface to a digital
circuit combined with a channel service unit; converts a customer's data stream
to bipolar format for transmission.
- Data Set
Ready: (DSR) A member of the control signal category of the RS232-C DTE-DCE
interface. DSR is used to indicate that the DCE is operational.
- Data Terminal Equipment: (DTE) A device which acts as the
origin of, or destination for, data. Examples are a computer, terminal or
- Data Transfer Rate: The average number of bits, characters,
or blocks per unit of time transferred from a data source to a data
- Database Server: A computer that stores data centrally for
network users & managers & often uses client-server software to distribute the
processing of that data between itself & nodes requesting
- Datagram: A block of data that is "smart" enough
(actually, which carries enough information) to travel from one Internet site
to another without having to rely on earlier exchanges between the source &
destination computers. In the Internet Protocols (IP), this refers to a packet
containing destination address & data.
Digital Service: (DDS) A private line digital service offered intraLATA buy
BOCs & interLATA by AT&T communications, with data rates typically at 2.4, 4.8,
9.6 & 56 Kbps; part of the services listed by AT&T under the Accunet
- dB: See Decibel
- DB-15: A
standardized connector with 15 pins for Ethernet transceivers
- DB-9: A
standardized connector with 9 pins for token ring & serial
- DC: See Direct
- DCE: See Data Communications
Equipment or see Distributed Computing
- DDD: See Direct Distance
- DDN: See Defense Data
- DDS: See Dataphone Digital
- De facto Standard: An unofficial standard that exists
because it is widely used by companies in the industry.
- De jure
Standard: A standard that has been officially approved by an organization
established to define & develop standards.
- Decentralize: The process
of distributing responsibility from a central point to several local points of
- Decibel: (dB) The unit for measuring the
relative strength of a signal. One-tenth of a Bel. It is equal to 10 times the
logarithm of the power ratio, 20 times the log of the voltage ratio, or 20
times the log of the current ratio. One decibel is the amount by which the
pressure of a pure sine wave of sound must be varied in order for the change to
be detected by the average human ear.
- DECnet: Digital Equipment
Corporation's proprietary network architecture that works across all of the
company's machines; endowed with a peer-to-peer methodology.
Line: Transmission medium, usually telephone lines, reserved for exclusive
use of a customer. These lines are not routed through the switching equipment
at the telephone company facilities.
- Dedicated Server: A node on
which applications are limited to maintaining network resources; no user
applications are available.
- Defense Data Network:
(DDN) A global communications network that serves the US Department of Defense.
It is made up of a network called NILNET
- DEK: See Data Encryption Key
- Delay: In communications, the
time between two events. Typically the time it takes for circuits to react to
- Demarcation Point: A point where operations control or
- Demodulation: The process of retrieving
information (data) from a modulated carrier signal. Reverse of modulation. DES:
(Data Encryption Standard) A scheme approved by the National Bureau of
Standards that encrypts data for security purposes. DES is the data-
communications encryption standard specified by Federal Information Processing
- Destination Field: A field in a message header that contains
the address of the station to which a message is being directed.
(Fiber Optic): A device that picks up light from fiber & converts the
information into an electrical signal.
- Device: As related to
workstation, a device is an item such as a telephone, personal computer or a
graphic or video terminal. Dial-Up Line: A telephone line in which the
connection between the DTE's is established by dialing. It is similar to
dialing from a common telephone set.
- DID: See Direct
- Dielectric: Non-metallic. All-dielectric cables
are nonconductive, contain no metal & are lightning
- Digital: Referring to communications procedures,
techniques, & equipment by which information is encoded as either a binary one
(1) or zero (0); the representation of the information in discrete binary form,
discontinuous in time; compare with analog.
Audio Tape: (DAT) Medium for storing digital rather than analog
- Digital Network Architecture: (DNA) Digital
Equipment Corporation's layered data communications protocol.
- Digital Visual Interface: (DVI) An interface used with high
resolution high speed displays. The video information is sent from the source
to the display in digital format for more accuracy. The digital data is
uncompressed data. Click here to see more
information on DVI including connectors.
- DIN: Deutsches Institiute
- Direct Burial Cable: A cable installed directly in the earth
without a conduit.
- Direct Current: (DC) An
electrical current whose electrons flow in one direction only. It may be
constant or pulsating as long as its movement is in the same
- Direct Distance Dialing: (DDD) A
telephone service with which a subscriber can call someone outside the area
without requiring operator assistance.
- Direct Inward
Dialing: (DID) A telephone service with which subscribers can have calls
within a system routed to a specific telephone without switchboard
- Direct Memory Access: (DMA) A method
of moving data from a storage device to RAM.
- Disk Duplexing: Fault
tolerance method in which two disk controllers are used in a single
- Disk Operating System: (DOS) Developed by
Microsoft to run on IBM computers.
- Disk/File Server: A mass storage
device that can be accessed by several computers; enables the creation,
storage, & sharing of files.
- Dispersion: The cause of bandwidth
limitations in an optical fiber. Dispersion causes a broadening of input pulses
along the length of the fiber. Two major types are (a) mode dispersion caused
by differential optical path lengths in a multimode fiber, & (b) material
dispersion caused by a differential delay of various wavelengths of light in a
wave guide material.
- Distortion: Any undesired change in a wave form
- Distributed Computing Environment:
(DCE) An architecture based on standard programming interfaces, conventions &
server functionalities used for distributing applications transparently across
networks. The DCE is controlled & promoted by the Open Software Foundation
(OSF) a consortium of vendors including DEC, IBM and Hewlett Packard.
- Distributed Queue Dual Bus: (DQDB) A communication
technique proposed for MANs (Metropolitan Area Networks).
Cable: In a CATV system, the transmission cable between the distribution
amplifier & the drop cable.
- Distribution Frame: A wall mounted
structure for terminating telephone wiring, usually the permanent wires from or
at the telephone central office where cross-connections are readily made to
extensions; also called distribution block.
- DLC Characters: The
special characters specified by interchange codes to implement the Data Link Control (DLC) functions.
- DMA: See Direct Memory Access
- DNA: See Digital Network Architecture
- DNS: See Domain Name Service
- Domain: A collection of network
devices that create a subgroup of a network. A domain can be created for
logical, functional or geographic needs.
- Domain Name
Service: (DNS) A static, hierarchical name service used with TCP/IP hosts,
& is housed on a number of servers on the Internet. Basically, it maintains a
database for figuring out & finding (or resolving) host names & OP addresses on
the Internet. this allows users to specify remote computers by host names
rather than numerical IP addresses. The advantage of the DNS is that you don't
have to remember numerical OP addresses for all the Internet sites available to
- DOS: See Disk Operating System
Address: The common notation for IP addresses of the form 220.127.116.11. where
each number represents one byte in the four-byte IP address. Also knows as
Dotted Decimal Notation.
- Downline Loading: The process of sending
programs (or other "nondata" type information) from a central source to
- Download: The transfer of either a system or
program from a disk file at one node to the memory of another computer. It is
the activity of loading software into the nodes of a network from one node or
device over the network media. Typically to Download is to load a file from a
remote server to your computer.
- Downtime: The period during which
computer or network resources are unavailable to users because of
- DQDB: See Distributed Queue Dual
- Drain Wire: An uninsulated wire in contact with a shield
through its length. Used for terminating the shield.
- Driver: A
software module that, under control of the processor, manages an I/O port to an
external device, such as serial RS232C port to a modem.
- Drop Cable:
In a local area networks, a cable that connects the main network cable, or bus,
& the data terminal equipment (DTE).
- DSR: See Data
- DSU: See Data Service
- DTE: See Data Terminal
- DTMF: See Dual-Tone
- DTS: Data Terminal Service
Homing: A method of connecting devices in which there is a primary
connection & a standby connection.
Multiple-Frequency: (DTMF) The audio signaling frequency on touch-tone,
- Duct: An underground or overhead tube for
carrying electrical conductors.
- Duplex: Two way data
- DVI: See Digital Visual