D4 framing DA DACS
daemon DANTE DARPA
DARPA Internet DAS DAT
data database concepts data bit
data channel
data flow control layer Datagram Data Link Layer
data link control layer DATANET 1 DATAPAC
datapak data sink
data stream Datex-1 Datex-p
dB (Decibel) dBm DCA
DCD DCE
D channel DCL DDE
DDL DDN DDN NIC
DDN X.25 DDR DDS
deadlock DECnet DECnet routing
dedicated line
de facto standard default Default Route
de jure standard DEK delay
demarc demodulation demultiplex
DENet
DES designated router destination address
Deutsches Forschungsnetz device DHCP
Diagnostic
Dialup dial backup dial-on-demand routing
dial-up line DIF differential encoding
differential Manchester encod. Dijkstra's algorithm Digital
Digital Loopback DIME DIN connector
directed search directory services Directory Access Prot. (X500)
DISA Disassembling distance vector routing algorfithm
distortion distortion delay Distributed Computing Environment (DCE)
Distributed Database DIX Ethernet DLC
DLCI DLL DMA
DNA DNS Document
DoD Domain DOMPAC
Dotted Quad DOV downlink station
dpi DPMI DQDB
DRAM drop DS/DD
drop cable DS-0 DS-1
DS-1/DTI DS-2 DS-3
DS-4 DSA DSL
DSP DSR
DSU DSX-1 DTE
DTR DTMF DUA
dual-homed station Dual IS-IS DUT
DVI DXI Dynamic Adaptive Routing
dynamic address resolution dynamic routing
D4 framing Framing
format used on most existing 1.544-Mbps facilities.
DA (Desk Accessory).
DACS (Digital Access and
Cross-Connect System). A computerized or manual facility wich allows DS-1/T1
lines to be remapped electronically at the DS-0 (64 kbps) level. Also called
DCS or DXS.
daemon A background process
(pronounced "demon") that carries out tasks on behalf of every user. Daemons
spend most of their time sleeping until something comes along which requires
their help. A UNIX system has a lot of daemons.
DANTE
(Delivering Advanced Network Technology to Europe). The launch
of DANTE in July 1993 marked an important milestone in the history of European
research networking. Set up to provide advanced international computer
network services for the European research community, DANTE's services
complement those provided by the national research networks. The company
plays a unique role in Europe, taking advantage of economies of scale and
focusing efforts towards the establishment of a high-quality computer network
infrastructure for European researchers.
DARPA (Defense Advanced
Research Projects Agency). An agency of the U.S. Department of Defense
responsible for the development of new technology for use by the military.
DARPA (formerly known as ARPA) was responsible
for funding much of the development of the Internet we know today, including
the Berkeley version of Unix and TCP/IP. [Source: NNSC]
DAS (Dual-Attached
Station). Also known as a Class A station, a DAS is a device attached to
both FDDI rings. If the primary ring
breaks, the station can use the secondary ring.
DAT (Digital AudioTape).
Data Information represented
in digital form, including voice, text, facsimile and video.
data bit In asynchronous
transfers, a character is composed of data bits (the actual information)
and framing bits (Start bit, Stop
bit/s, Parity bit).
database concepts A database
is the name given to the combination of a program that can manipulate data,
together with the data that it acts upon.
a record is a set of data about a person or item. Name, telephone
number and postcode is an example of such a set.
a field is one part of that record; the postcode for example.
a delimiter character separates each field from the field preceding
it and the field that follows it. A colon (:) is often used as a field
delimiter.
a key is the field or part of a field that the program uses
when it acts on the data.
data channel In SNA,
a device that connects a processor and main storage with peripherals. See
also channel.
data flow control layer Layer
5 of the SNA architectural model. The data flow control layer processes
requests and responses that are exchanged between session partners.
Datagram The basic unit
of information passed across the Internet. It contains a source and destination
address along with data. Large messages are broken down into a sequence
of IP datagrams. [Source: ZEN]
Data Link Layer The
OSI layer that is responsible for data transfer across a single physical
connection, or series of bridged connections, between two Network entities.[Source:
RFC1208]
data link control layer Layer
2 in the SNA architectural model.
DATANET 1 A major Netherlands
PSDN.
DATAPAC A large Canadian
PSDN.
datapak Packet -switched
public network in the Nordic countries.
data sink Network equipment
that accepts data transmissions.
data stream All data
transmetted through a communications line in a single read or write operation.
Datex-1 Circuit-switched
public network in Germany.
Datex-p Packet-switched
public network in Germany.
dB (Decibel) Unit for
measuring relative strength (ratio) of two signals.
dBm A measure of power in
communications: the decibel in reference to one milliwatt (0dBm = 1 milliwatt
and 30 dBm = .001 milliwatt).
DCA See: Defense
Information Systems Agency
DCD (Data Carrier Detect) -
Modem signal. See: CD
DCE (Data Circuit-terminating
Equipment). The equipment providing functions wich establish, maintain
and terminate a data transmission connection (such as a Modem)
D channel Full-duplex,
16-Kbps (basic rate) or 64-Kbps (primary rate) ISDN
channel.
DCL (Digital Command Language)
DEC.
DDE (Dynamic Data Exchange).
A communications channel that allows compatible programs to exchange data
and control other applications in Windows, OS/2,
and Presentation Manager.
DDL (Document Description
Language) OR (Database Description Language).
DDN (Defense Data Network).
A global communications network serving the US Department of Defense composed
of MILNET, other portions of the
Internet, and classified networks which are not part of the Internet. The
DDN is used to connect military installations and is managed by the Defense
Information Systems Agency. See also: DISA [Source:
RFC1392]
DDN NIC (Defense Data Network
Network Information Center). Often called "The NIC", the DDN NIC's primary
responsibility is the assignment of Internet network addresses and Autonomous
System numbers, the administration of the root domain, and providing information
and support services to the DDN. It is also a primary repository for RFCs.
See also: Autonomous System, Network
Address, Internet Registry, Network
Information Center, Request For Comments.[Source:
RFC1392]
DDN X.25 U.S. DoD
standard protocol very similar to X.25
used for connections to the DDN.
DDR (Dial-on-Demand
Routing). A technique whereby a router can automatically initiate and close
a circuit-switched session. DDR permits routing over ISDN
or phone lines using an external ISDN terminal
adapter (TA) or modem. The router communicates to the TA what numbers
to dial using the V.25bis
protocol.
DDS (Dataphone Digital Service).
A trademark of AT&T identifying a private line service for digital
data communications.
deadlock Unresolved
contention for the use of a resource. In APPN,
when two elements of a process each wait for action by or a response from
the other before they resume the process.
DECnet A proprietary network
protocol designed by Digital Equipment Corporation. The functionality of
each Phase of the implementation, such as Phase IV and Phase V, is different.[Source:
RFC1392]
DECnet routing Introduced
in DECnet Phase III, Digital's proprietary routing scheme. In DECnet Phase
V, DECnet completed its transition to OSI routing protocols (ES-IS
and IS-IS).
dedicated line A communications
line that is not switched. When the line is not owned by the user, the
term leased line is more common.
de facto standard A
standard by usage rather than official degree a default standard.
default A value to which
some variable is automatically set, unless an alternative value is provided
by the user.
Default Route A
routing table entry which is used to direct packets addressed to networks
not explicitly listed in the routing table. [Source: MALAMUD]
de jure standard A
standard by official degree.
DEK (Data Encryption Key) Used
for the encryption of message text and for the computation of message integrity
checks (signatures). See also: Encryption.[Source:
RFC1392]
delay The time between
the initiation of a transaction by a sender and the first response received
by a sender. Also, the time required to move a packet from source to destination
over a given path.
demarc Demarcation
point between carrier equipment and private telephone equipment (CPE)
demodulation Process
of returning a modulated signal to its original form. Modems perform demodulation
by taking an analog signal and returning it to its original (digital) form.
demultiplex To separate
from a common input into multiple output streams.
DENet
The Danish research network, operated by UNI-C
DES (Data Encryption Standard) A
popular, standard encryption scheme. See also: Encryption.[Source:
RFC1392]
designated router A
designated OSPF router generates a
link state advertisement for a multiaccess network and has other special
responsibilities in the running of the protocol. In OSPF, each multiaccess
network that has at least two attached routers has a designated router.
The designated router is elected by the OSPF Hello Protocol. The designated
router concept anables a reduction in the number of adjacencies required
on a multiaccess network. This in turn reduces the amount of routing protocol
traffic and the size of the topological database.
destination address Address
of a receiving network device.
Deutsches
Forschungsnetz The DFN, "Deutsches Forschungsnetz" is the
German national research and academic network.
device An entity that
can access a network. Used interchangeably with node.
DHCP (Dynamic Host Configuration
Protocol).Established to lessen the administrative burden of manual configuration
of TCP/IP Hosts on a network. WINS
supports DHCP by supporting dynamic name registration, DNS
doesn't. Using DHCP for WINS resolution provides safe, reliable and simple
TCP/IP network configuration.
Diagnostic Procedures
and systems wich detect and isolate a malfunction or mistake in a communications
device, network or system.
Dialup A temporary, as
opposed to dedicated, connection between machines established over a standard
phone line.[Source: RFC1392]
dial backup Feature
supported by Cisco routers that provides protection against WAN down time
by allowing the network administrator to configure a backup serial line
through a circuit-switched connection.
dial-on-demand routing Cisco
routing feature that provides on demand network connections in an environment
using the Public Switched Telephone Network (PSTN).
dial-up line Communications
circuit that is established by a switched-circuit connection using the
telephone network.
DIF (Data Interchange Format).
differential encoding Digital
encoding technique whereby a binary value is denoted by a signal change
rather than a particular signal level.
differential Manchester encoding
Digital coding scheme where a mid-bit-time transition is used
for clocking , and a transition at the biginning of each bit time denotes
a zero. The coding scheme used by IEEE
802.5/Token Ring network.
Dijkstra's algorithm A
shortest-path routing algorithm that iterates on lengh of path to determine
a shortest-path spanning tree. Commonly used in link-state routing algorithms.
See also distance vector routing algorithm and link-state routing algorithm.
Digital The binary ("1/0")
output of a computer or terminal. In data communication, an alternating,
non-continuous (pulsating) signal.
Digital Loopback A
technique for testing the digital processing circuitry of a communications
device. The loopback is toward the line side of a modem, but tests most
of the circuitry in the modem under test.
DIME (Dual Independent Map
Encoding)
DIN connector Deutsche
Industrie Norm (German Industrial Standard) connector. A connector on a
network processor panel that connects an FDDI
module to an external optical bypass switch.
directed search A search
request sent to a specific node known to contain a resource. A directed
search is used to determine the continued existance of the resource and
to obtain routing information specific to the node.
Directory Access Protocol (X.500) Protocol
used for communication between a Directory User Agent and a Directory System
Agent. [Source: MALAMUD]
directory services Services
that help network devices locate service providers.
DISA (Defense Information
Systems Agency). Formerly called the Defense Communications Agency (DCA),
this is the government agency responsible for managing the DDN portion
of the Internet, including the MILNET. Currently, DISA administers the
DDN, and supports the user assistance services of the DDN NIC. See also:
Defense Data Network.[Source: RFC1392]
Disassembling Converting
a binary program into human-readable machine language code. [Source: ZEN]
distance vector routing algorithm
Also called Bellman-Ford
routing algorithm. A class of routing algorithms that iterate on the
number of hops in a route to find a shortest-path spanning tree. Distance
vector routing algorithms call for each router to send its entire routing
table in each update, but only to its neighbors. Distance vector routing
algorithms can be prone to routing loops, but are computationally simpler
than their routing counterparts, link-state routing algorithms. See also
link-state routing algorithm
and Dijkstra's algorithm].
Distortion The unwanted
change in waveform occurring between two points in a transmission system.
distortion delay Problem
with a communication signal resulting from non uniform transmission speeds
of the components of a signal through a trasmission medium.
Distributed
Computing Environment (DCE) An architecture of standard programming
interfaces, conventions, and server functionalities (e.g., naming, distributed
file system, remote procedure call) for distributing applications transparently
across networks of heterogeneous computers. Promoted and controlled by
the Open Software Foundation (OSF),
a consortium led by Digital, IBM and Hewlett Packard. [Source: RFC1208]
Distributed Database
A collection of several different data repositories that looks
like a single database to the user. A prime example in the Internet is
the Domain Name System.[Source: RFC1392]
DIX Ethernet See:
Ethernet
DLC )Data Link Control
layer). SNA layer responsible for transmission of data between two nodes
over a physical link.
DLCI (Data Link Connection
Identifier). A Frame Relay value that identifies a logical connection.
DLL (Dynamic Link Library).
The ability in Windows and OS/2 for executable memory to call software
libraries (i.e subrroutines, or code for accomplishing specific functions)
not previously linked to the executable.
DMA (Direct Memory Access).
DoD (Department of
Defense). United States government organization that is responsible for
the nation's defense. The DoD has frequently funded communication protocol
development.
DOV (Data Over Voice). A
technology for transmitting data and voice simultaneously over Twisted
Pair copper wiring.
DNA (Digital Network Architecture).
DEC Architecture.
DNS (Domain Name System).
The DNS is a general purpose distributed, replicated, data query service.
The principal use is the lookup of host IP addresses based on host names.
The style of host names now used in the Internet is called "domain name",
because they are the style of names used to look up anything in the DNS.
Some important domains are: .COM (commercial), .EDU (educational), .NET
(network operations), .GOV (U.S. government), and .MIL (U.S. military).
Most countries also have a domain. For example, .US (United States), .UK
(United Kingdom), .AU (Australia). It is defined in STD
13, RFCs 1034
and 1035.
See also: Fully Qualified Domain Name.[Source:
RFC1392]
Document Unit of information
sent from servers to clients; a document may contain plain or formatted
text, in-lined graphics, sound, other multimedia data, or hyperlinks to
other documents.
Domain In the Internet,
a part of a naming hierarchy. Syntactically, an Internet domain name consists
of a sequence of names (labels) separated by periods (dots), e.g., "tundra.mpk.ca.us."
In OSI, "domain" is generally used as an administrative partition of a
complex distributed system, as in MHS
Private Management Domain (PRMD),
and Directory Management Domain (DMD).[Source: RFC1208].
For a list of the Internet domains see also: domains.html
and/or the official ISO document ISO3166_codes.
DOMPAC A large French
Guiana PSN.
Dotted quad A set
of four numbers connected with periods that make up an Internet address;
for example, 147.31.254.130 [Source: ZEN]
downlink station See
ground station
dpi (Dots Per Inch). A measure
of screen and printer resolution.
DPMI (DOS.Protected Mode
Interface)
DQDB (Distributed Queue
Dual Bus). Communication protocol proposed IEEE
802.6 committee for use in MANs.
DRAM (Dynamic RAM)
drop A point on a multipoint
channel where a connection to a networked device is made.
drop cable Generally,
a short cable that connects a network device (such as a computer) to a
physical medium. A type of AUI.
DS/DD (Double-Sided, Double-Density).
DS-0 A single 64-Kbps
channel of a DS-1 digital facility.
DS-1 Digital (transmission)
System 1, or Digital Signal level 1. Term used to refer to the 1.44-Mbps
(U.S.) or 2.108-Mbps (Europe) digital signal carried on a T1
facility.
DS-1/DTI Domestic trunk
interface circuit to be used for DS-1 applications with 24 trunks.
DS-2 (Digital Signal 2).
Four T1 frames packed into a higher level
frame transmitted at 6.312 Mbps. [Source: ADSL
Forum]
DS-3 Digital (transmission)
System 3, or Digital Signal level 3. Term used to refer to the 44-Mbps
digital signal carried on a T3 facility.
DS-4 Digital Signal
level 4. Bell System terminology for the 274.176 Mbps signal.
DSA (Directory System Agent)
The software that provides the X.500 Directory Service for a portion of
the directory information base. Generally, each DSA is responsible for
the directory information for a single organization or organizational unit.
[Source: RFC1208]
DSL (Digital Subscriber
Line). Modems on either end of a single twisted pair wire that delivers
ISDN Basic Rate Access. [Source: ADSL
Forum]
DSP (Domain Specific
Part). That part of the CLNS addresses
thet contains an area identifier, a station identifier, and a selector
byte.
Also: (Digital Signal Processor)
DSR (Data Set Ready).
An RS-232-C interface circuit that
is activated when the DCE is powered uo and ready for use.
DSU (Data Service Unit).
A device used in digital transmission for connecting data terminal equipment
(DTE), such as router, to a digital transmission
circuit (DTC) or service.
Also:
(Digital Service Unit). A user device interfacing to a digital circuit
(such as DDS or T1
when combined with a CSU). The DSU converts,
the user's data stream to bipolar format for transmission.
DSX-1 Cross-connection
point for DS-1 signals.
DTE (Data Terminal Equipment).
A device transmitting data to, and/or receiving data from, a DCE
(for example, a terminal or printer). Also the part of a data station that
serves as a data source, destination, or both, and that provides for the
data communications control function according to protocols. DTE includes
computers, protocol translators and multiplexers.
DTR (Data Terminal Ready).
A modem interface control signal sent from the DTE
to the modem, usually telling the modem that the DTE is ready to transmit
data.
DTMF (Dual Tone Multifrequency).
Use of the two simultaneous voice-band tones for dialing (such as touch
tone).
DUA (Directory User Agent).
The software that accesses the X.500
Directory Service on behalf of the directory user. The directory user may
be a person or another software element. [Source: RFC1208]
dual-homed station A
device attached to multiple FDDI rings.
Dual homing provides redundancy.
Dual IS-IS See Integrated
IS-IS.
DUT (Device Under Test).
DVI (Digital Video Interactive).
A system that compresses digital video and audio data for use on a personal
computer..
DXI Data Exchange Interface.
The Interface between a router and a special DSU
that can perform segmentation and reassembly.
Dynamic Adaptive
Routing Automatic rerouting of traffic based on a sensing and
analysis of current actual network conditions. NOTE: this does not include
cases of routing decisions taken on predefined information. [Source: J.
Postel]
dynamic address resolution Use
of an address resolution protocol to determine and store address information
on demand.
dynamic routing Routing
that adjusts automatically to network topology or traffic changes. Also
adaptive routing.