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D-bit
=====
Delivery confirmation bit.
-------------------------------------------------------------------------------
daisy chain
===========
A system that connects peripheral devices to the computer along
a single bus so that the device closest to the central processing
Unit (CPU) is serviced first.
-------------------------------------------------------------------------------
Data Access Arrangement (DAA)
=============================
Data communications equipment furnished or approved by a common
carrier, permitting attachment of privately owned data terminals.
-------------------------------------------------------------------------------
Data Carrier Detect (DCD)
=========================
A modem interface signal indicating that the carrier frequency has
been received and the modem is now ready for data transmission.
-------------------------------------------------------------------------------
Data Circuit-terminating Equipment (DCE)
========================================
Any piece of equipment that provides the functions required to
establish, maintain, and terminate a connection and convert and
code those signals required between Data Terminal Equipment (DTE)
and a the data communications facility. A modem is an example of
a DCE on an analog communications facility; a data service unit
is an example of a DCE on a digital communications facility.
-------------------------------------------------------------------------------
Data Link Escape (DLE)
======================
A control-character sequence (two-characters) used exclusively to
provide supplementary line-control signals (control-character
sequences or DLE sequences). The first character is DLE; the second
character varies according to the function desired and the code used.
See reverse interrupt.
-------------------------------------------------------------------------------
Data Network Identification Code (DNIC)
=======================================
A 4-digit code used to address a data network across national
boundaries. The DNIC is required as part of the CCITT X.121 address.
The first three digits identify the country or geographic area, and
the last digit identifies the network.
The TYMNET network DNIC is 3106.
-------------------------------------------------------------------------------
data processing
===============
One or more operations performed on data to achieve a desired
objective. Also called information processing.
-------------------------------------------------------------------------------
Data Set Ready (DSR)
====================
A handshaking (flow control) signal used to notify the DTE that the
modem (data set) is connected, powered-up, and ready to receive.
-------------------------------------------------------------------------------
data sink
=========
The receiving end of a communications link. Contrast with data source.
-------------------------------------------------------------------------------
data source
===========
The transmitting end of a communications link. Contrast with data sink.
-------------------------------------------------------------------------------
Data Terminal Equipment (DTE)
=============================
A piece of equipment that provides an entry or exit point for user
data in a communication network. For example, a terminal operating
with the defined protocol for the network is a DTE.
-------------------------------------------------------------------------------
Data Terminal Ready (DTR)
=========================
A handshaking (flow control) signal used to signal the modem
(data set) that the DTE is connected, powered up, and ready
to receive.
-------------------------------------------------------------------------------
Data Transfer Bus (DTB)
=======================
A 16- or 32-bit bus used to carry data from one functional unit to
another. See VMEbus.
-------------------------------------------------------------------------------
database
========
A collection of data that is indexed, filed, or organized according
to specific rules so that desired data can be retrieved. A database
is designed to allow multiple appli- cations to access the data, to
have minimal redundancy of data, and to allow for growth and change.
-------------------------------------------------------------------------------
Database Management System (DBMS)
=================================
A comp9ehensive software system that builds, maintains, and provides
access to a database.
-------------------------------------------------------------------------------
datagram (DG)
=============
A method of sending messages (packets) with self-contained information
enabling a packet to reach its destination. See message switching.
------------------------------------------------------------------------------
Datalink level
==============
Level 2 of the Open Systems Interconnection (OSI) model. The Datalink
level ensures error-free data transmission between a host and the
network and transfers information units to the end of this link.
Recommendations are outlined for framing and synchronization, error
control and recovery, link initialization and disconnection,
addressing and message sequence control.
-------------------------------------------------------------------------------
Datapac
=======
A data communications service provided in Canada.
-------------------------------------------------------------------------------
daughter card
=============
Serial Input/Output (SIO) interface board. A board in the Engine,
Mini-Engine, and Compact XL that transfers synchronous and
asynchronous communications signals from the network to the SIO
Controller board. There can be up to eight SIO interface boards
attached to one SIO Controller board.
-------------------------------------------------------------------------------
DBMS
====
Database Management System. A comprehensive software system that
builds, maintains, and provides access to a database.
-------------------------------------------------------------------------------
DCD
===
Data Carrier Detect. A modem interface signal indicating that the
carrier frequency has been received and the modem is now ready for
data transmission.
-------------------------------------------------------------------------------
DCE
===
Data Circuit-terminating Equipment. Any piece of equipment that
provides the functions required to establish, maintain, and terminate
a connection and convert and code those signals required between Data
Terminal Equipment (DTE) and a the data communications facility.
A modem is an example of a DCE on an analog communications facility;
a data service unit is an example of a DCE on a digital
communications facility.
-------------------------------------------------------------------------------
DCF
===
Dedicated Customer Facility.
-------------------------------------------------------------------------------
DDCMP
=====
Digital Data Communications Message Protocol. Transmis-sion of data
between stations in a point-to-point or multi-point system. The
method of physical data transfer may be parallel, serial synchronous,
or serial asynchronous. BT North America supports DDCMP,
transparently, through the 2780/3780/HASP interface.
-------------------------------------------------------------------------------
DDD
===
Direct Distance Dialing. A telephone exchange service that enables
the user to directly dial outside the local area without operator
assistance.
-------------------------------------------------------------------------------
DDP
===
Distributed Data Processing.
-------------------------------------------------------------------------------
DDT
===
Dynamic Debugging Tool. A program that permits the user to log into
the Kernel and load or examine the contents of a slot, change
contents of memory locations, or perform various special diagnostic
operations. DDT allows a user access to individual slots within an
ISIS node.
-------------------------------------------------------------------------------
dead-ended circuit
==================
A partial circuit that ends without being terminated, for example, a
link channel or a node that is only connected to one other node.
-------------------------------------------------------------------------------
debug
=====
The process of tracing and correcting errors in software or hardware.
Also called troubleshooting.
-------------------------------------------------------------------------------
debugger
========
A set of routines that allows users to examine and change memory
content and start or stop the execution of instructions.
-------------------------------------------------------------------------------
DEC System 10
=============
A type of Digital Equipment Corporation (DEC) host main-frame
computer. When used with a TYMNET operating system and connected to
a TYMNET network, it is called TYMCOM-X.
-------------------------------------------------------------------------------
dedicated
=========
A communication circuit that always transmits over the same
physical route. A dedicated circuit is normally a permanent
connection. Also, a service, number, or connection that is reserved
for the use of a single customer.
-------------------------------------------------------------------------------
Dedicated Terminal Interface (DTI)
==================================
Terminal interface (TIF) software residing in a slot (within a node
in a shared network) that is reserved for the use of a specific
customer.
-------------------------------------------------------------------------------
Deferred-Echo Mode (DEM)
========================
A method of operation whereby the destination interface has the
responsibility for echoing all characters back to the origination
device. See also Leave Deferred-Echo Mode and Enter Deferred-Echo
Mode.
-------------------------------------------------------------------------------
delay-distortion
================
A problem caused when some frequencies travel slower than others
over the transmission path. The maximum difference in transmission
time between any two frequencies in a specified frequency band.
Expressed in microseconds.
-------------------------------------------------------------------------------
delay-measurement circuit
=========================
A circuit that is built through XRAY to measure the throughput delay
in a specified portion of a network.
-------------------------------------------------------------------------------
delimiter
=========
A character that separates and organizes elements of data.
-------------------------------------------------------------------------------
DEM
===
Deferred-Echo Mode. A method of operation whereby the destination
interface has the responsibility for echoing all characters back to
the origination device. See also Leave Deferred-Echo Mode and Enter
Deferred-Echo Mode.
-------------------------------------------------------------------------------
demodulation
============
The process of converting an analog signal to a digital signal;
a DCE receives an analog signal, varies that signal to make it a
digital signal, and sends that digital signal to a DTE.
-------------------------------------------------------------------------------
Design Objective (DO)
=====================
The first document written in the development cycle. An NTD document
that describes, in general terms, the product being developed, its
function, how the product relates to other products, and the
performance and interface constraints that should be met. Product
Marketing may provide appropriate information for this document.
Interfaces to other products are included. Sometimes the project
initiation request (PIR) clearly states the objectives to be achieved
and there is no need for the DO.
-------------------------------------------------------------------------------
destination address
===================
The address specifying the destination of a circuit.
-------------------------------------------------------------------------------
destination host
================
An address on a destination node to which a circuit is built for a
BT North America user session. Contrast with origination host.
-------------------------------------------------------------------------------
destination list
================
A list of possible destination items (targets), for example, host,
name, group. Contrast with origination list.
-------------------------------------------------------------------------------
destination name
================
Access profile in the Master User Directory (MUD) that describes a
destination, either host name or X.121 name.
(Formerly called host name.)
-------------------------------------------------------------------------------
destination node
================
A node to which a circuit is built in a network. This node usually
serves as a host interface (HIF). Contrast with origination node.
-------------------------------------------------------------------------------
detach line
===========
The process by which a program detaches a line from a link.
-------------------------------------------------------------------------------
detached port
=============
A channel that is used to put a circuit temporarily in limbo because
the circuit could not be completed to the requested destination; the
circuit is eventually zapped.
-------------------------------------------------------------------------------
Deutsche Industrie Norm (DIN)
=============================
A set of standards for electronic products that originated in Germany.
The Turbo Engine boards use 96-pin DIN connectors.
-------------------------------------------------------------------------------
DG
==
Datagram. A method of sending messages (packets) with self-contained
information enabling a packet to reach its destination. See message
switching.
-------------------------------------------------------------------------------
diagnostic
==========
Detection and isolation of an error in a program or a malfunction in
equipment. Also, an error message printed in a program list by a
compiler or an assembler.
-------------------------------------------------------------------------------
dial-up line
============
A communications circuit that is established by a switched telephone
circuit connection. See circuit switching.
-------------------------------------------------------------------------------
dibit
=====
A group of two bits. The four possible states of a dibit are 00, 01,
10, and 11.
-------------------------------------------------------------------------------
dibit encoding
==============
Modulation techniques that enable one signal element to convey two
bits of information.
-------------------------------------------------------------------------------
DIC
===
Data Interchange Code.
-------------------------------------------------------------------------------
digital
=======
An electrical signal made up of discrete pulses. In data
communications, the pulses are coded to represent information.
Contrast with analog.
-------------------------------------------------------------------------------
digital circuit
===============
A circuit that transmits data in a digital form. Contrast with the
standard voice-grade phone line (an analog circuit, which requires
a computer or terminal to convert data into an analog format).
-------------------------------------------------------------------------------
digital computer
================
A computer that manipulates discrete data and performs arithmetic and
logic operations on these data. Contrast with analog computer.
-------------------------------------------------------------------------------
Digital Data Communications Message Protocol (DDCMP)
====================================================
Transmission of data between stations in a point-to-point or a
multipoint system. The method of physical data transfer may be
parallel, serial synchronous, or serial asynchronous. BT North
America supports DDCMP, transparently, through the 2780/3780/HASP
interface.
-------------------------------------------------------------------------------
DIN
===
Deutsche Industrie Norm. A set of standards for electronic products
that originated in Germany. The Turbo Engine boards use 96-pin DIN
connectors.
-------------------------------------------------------------------------------
Direct Distance Dialing (DDD)
=============================
A telephone exchange service that enables the user to directly dial
outside the local area without operator assistance.
-------------------------------------------------------------------------------
Direct Memory Access (DMA)
==========================
An internal mode of transfer that allows data to flow directly to and
from main memory. When applied to a BT North America base, it is the
transfer of data between a node and a host by way of one synchronous
line to the host's bus.
-------------------------------------------------------------------------------
direct-access
=============
The process of reading or writing information from an auxiliary
memory device by accessing the information directly.
-------------------------------------------------------------------------------
directive
=========
An assembly-language statement that influences the assembler through
instructions to assemble a program, part of a pro- gram, or the
contents of a listing, or to print a message to a user.
-------------------------------------------------------------------------------
directory
=========
A list of files kept by the operating system.
-------------------------------------------------------------------------------
disk
====
A direct-access storage medium.
-------------------------------------------------------------------------------
disk pack
=========
Multiple magnetic disks mounted vertically on a single shaft. Each
magnetic disk can be removed from the pack.
-------------------------------------------------------------------------------
diskette
========
A floppy disk.
-------------------------------------------------------------------------------
Dispatcher
==========
That portion of the ISIS or ISIS-68K operating system responsible for
communication between slots.
-------------------------------------------------------------------------------
Dispatcher Interface (DISPI)
============================
The Node Code process that communicates with the ISIS Dispatcher.
DISPI is the source of a circuit in an originating node and the
termination point of that circuit in the destination node.
-------------------------------------------------------------------------------
Display System Protocol (DSP)
=============================
A nonproprietary protocol used to support IBM 3270-type devices on
X.25 data across a packet-switched network. A data convention for
transmitting 3270 commands and response signals within and between
networks.
-------------------------------------------------------------------------------
distributed functions
=====================
Data processing functions performed by remote minicomputers and
intelligent terminals rather than a centrally located computer.
-------------------------------------------------------------------------------
distributed network
===================
A network in which each node allocates its own resources. Once a node
has received the Needle, from the Supervisor, with encoded information
for a circuit path, the node allocates resources to transfer the
Needle to the second node on the path. The second node allocates
resources to transfer the Needle to the third node, and so on, to the
destination node. See Needle.
-------------------------------------------------------------------------------
distribution tape
=================
A physical data storage medium used to transport BT North America
software release files.
-------------------------------------------------------------------------------
DLE
===
Data Link Escape. A control-character sequence (two- characters) used
exclusively to provide supplementary line-control signals
(control-character sequences or DLE sequences). The first character is
DLE; the second character varies according to the function desired and
the code used. See reverse interrupt.
-------------------------------------------------------------------------------
DLL
===
Down-Line Load. A software protocol used to transfer code from one
node to another.
-------------------------------------------------------------------------------
DMA
===
Direct Memory Access. An internal mode of transfer that allows data
to flow directly to and from main memory. When applied to a
BT North America base, it is the transfer of data between a node and
a host by way of one synchronous line to the host's bus.
-------------------------------------------------------------------------------
DNA
===
Dynamic Debugging Tool to Network Access.
-------------------------------------------------------------------------------
DNIC
====
Data Network Identification Code. A 4-digit code used to address a
data network across national boundaries. The DNIC is required as part
of the CCITT X.121 address. The first three digits identify the
country or geographic area, and the last digit identifies the network.
The TYMNET network DNIC is 3106.
-------------------------------------------------------------------------------
DNPA
====
Data Numbering Plan Area.
-------------------------------------------------------------------------------
DO
==
Design Objective. The first document written in the development cycle.
An NTD document that describes, in general terms, the product being
developed, its function, how the product relates to other products,
and the performance and interface constraints that should be met.
Product Marketing may provide appropriate information for this
document. Interfaces to other products are included. Sometimes the
project initiation request (PIR) clearly states the objectives to be
achieved and there is no need for the DO.
-------------------------------------------------------------------------------
DOS
===
Disk Operating System.
-------------------------------------------------------------------------------
down
====
State of host, node, or link.
-------------------------------------------------------------------------------
Down-Line Load (DLL)
====================
A software protocol used to transfer code from one node to another.
-------------------------------------------------------------------------------
down-load
=========
A process used to load code or dump code (transfer data or files to
another computer, node, or terminal). This procedure is performed
from a remote host.
-------------------------------------------------------------------------------
DRAM
====
Dynamic Random Access Memory. Random Access Memory that requires
refresh to keep data.
-------------------------------------------------------------------------------
drive
=====
A device that reads from and writes to a floppy disk, a magnetic disk,
or a tape. See disk.
-------------------------------------------------------------------------------
drowsiness factor
=================
The time added to the normal sleep time of a Supervisor. See sleeping.
-------------------------------------------------------------------------------
DSP
===
Display System Protocol. A nonproprietary protocol used to support
IBM 3270-type devices on X.25 data across a packet-switched network.
A data convention for transmitting 3270 commands and response signals
within and between networks. Also called Digital Signal Processor.
-------------------------------------------------------------------------------
DSR
===
Data Set Ready. A handshaking (flow control) signal used to notify
the DTE that the modem (data set) is connected, powered-up, and ready
to receive.
-------------------------------------------------------------------------------
DTB
===
Data Transfer Bus. A 16- or 32-bit bus used to carry data from one
functional unit to another. See VMEbus.
-------------------------------------------------------------------------------
DTE
===
Data Terminal Equipment. A piece of equipment that pro- vides an
entry or exit point for user data in a communication network. For
example, a terminal operating with the defined protocol for the
network is a DTE.
-------------------------------------------------------------------------------
DTI
===
Dedicated Terminal Interface. Terminal interface (TIF) software
residing in a slot (within a node in a shared network) that is
reserved for the use of a specific customer.
-------------------------------------------------------------------------------
DTR
===
Data Terminal Ready. A handshaking (flow control) signal used to
signal the modem (data set) that the DTE is connected, powered up,
and ready to receive.
-------------------------------------------------------------------------------
Dual Compact XL
===============
An intermediate-sized node in the Engine family of communications
processors. The Dual Compact XL is the same physical size as the
Compact XL; however, it uses a dual chassis backplane containing
two CPU IIIs, two MAC IIIs, and two SIO II boards, while supporting
two additional DMA I/O slots. See Compact XL.
-------------------------------------------------------------------------------
Dual-Mini-Engine
================
Two Mini-Engine systems in an Engine-size cabinet. See Mini-Engine.
-------------------------------------------------------------------------------
dumb terminal
=============
DTE without data processing capabilities, such as teletypes, visual
display units, and printers. Contrast with intelligent terminal.
-------------------------------------------------------------------------------
dummy record
============
A special frame used to maintain a minimum level of traffic on a
line when there is no valid data available. The dummy record does
not contain data and is automatically transmitted on a line every
half-second. Dummy records are transmitted over a multiple-line
link when all traffic is on other lines of the link.
-------------------------------------------------------------------------------
dump
====
A procedure for transferring data from a target's memory to an
auxiliary storage device such as a disk. Used when debugging code.
-------------------------------------------------------------------------------
Dynamic Debugging Tool (DDT)
============================
A program that permits the user to log into the Kernel and load or
examine the contents of a slot, change contents of memory locations,
or perform various special diagnostic operations. DDT allows a user
access to individual slots within an ISIS node.
-------------------------------------------------------------------------------
Dynamic Random Access Memory (DRAM)
===================================
Random Access Memory that requires refresh to keep data.
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<*> <*>
<*> This Concludes Part 4 of the Modernz Database <*>
<*> <*>
<*> MATRIX BBS (908) 905-6691 <*>
<*> World of Kaos NOW (908) WOK-NOW! <*>
<*> <*>
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