Glossary-D
A Data Communication Historical Series
By Bob Pollard

HOME                            INDEX

 

D CHANNEL:

1) Data Channel: Full-duplex, 16-kbps Basic Rate Interface (BRI), or 64-kbps Primary Rate Interface (PRI) Integrated Services Digital Network (ISDN) channel.

2) In Systems Network Architecture (SNA): A device that connects a processor and main storage with peripherals.

DAA:

Data Access Arrangement: Data communications equipment furnished or approved by a common carrier that facilitates attachment of privately owned data terminals and communications equipment to the common carrier's network.

DAAS:

Defense Automated Addressing System / DLA (Defense Logistic Agency): electronic messaging gateway station located at Dayton, OH and Tracy, Calif.

DAC:

1) Digital Analog Conversion: The method of converting digital data to analog data, as in analog sound to digital sound.

2) Dual-Attached Concentrator: FDDI or CDDI concentrator capable of attaching to both rings of a FDDI or CDDI network. It also can be dual-homed from the master ports of other FDDI or CDDI concentrators.

3) Discretionary Access Control: An access control service that enforces a security policy based on the identity of system entities and their authorizations to access system resources.

DACS:

Digital Access Cross-connect System: A switch that enables test access and switching of digital signals in a T system. AT&T term for a digital cross-connect system.

DAISEY CHAIN:

A method of serial device interconnection, which may also determine interrupt priority by connecting the interrupting sources serially.

DAP:

Directory Access Protocol: Protocol used between a Directory User Agent (DUA) and a Destination Service Access (DSA) in an X.500 directory system.

DARK FIBER:

Unused fiber optic cable: Versus, when it is carrying a signal it may be called ‘Lit fiber’.

DARPA: Obsolete term referring to the Internet

See Defense Advanced Research Projects Agency

DAS:

1) Dual Attachment Station: Device attached to both the primary and the secondary FDDI rings. Dual attachment provides redundancy for the FDDI ring; if the primary ring fails, the station can wrap the primary ring to the secondary ring, isolating the failure and retaining ring integrity.

2) Dynamically Assigned Socket: Socket that is assigned dynamically by DDP upon request by a client. In an AppleTalk network, the sockets numbered 128 to 254 are allocated as DAS(s).

DATA:

Refers to communicated Information or refers to any structured information: messages, facts, instructions, controls, concepts, etc.

DATA ACCESS ARRANGEMENT:

Refers to an electronic unit (device) used to connect (interface) user owned equipment to Telephone Company lines.

DATA ACQUISITION:

Refers to the act of recording (reading) data from another source, usually devices

DATABASE:

Normally refers to an organized collection of information.

DATA BLOCK:

A specific number of characters accumulated into a group or block then subsequently transmitted in a block form.

DATA CHANNEL:

Line, Circuit or Facility - The data transmission path between two or more stations

DATA CIRCUIT:

Communications channels (lines) provided specifically for the exchange of data as compared to voice or other information forms. Modern data terminals often operate effectively on channels not so designated, offering a user economy and flexibility of operation.

DATA COLLECTION:

The process of combining data received from several sources at one location in a file or queue for processing.

DATA COMMUNICATIONS:

The transmission of non-voice data in the form of messages and other types of information

DATA CONVERSION:

The process of converting data from one format to another; example: one character code set to another code set (Baudot to ASCII).

DATA DICTIONARY:

Glossary - A listing and/or description of all the data related names and elements.

DATA DIRECT VCC (Virtual Channel Connection):

In ATM, a bi-directional point-to-point VCC set up between two LEC(s); one of three data connections defined by Phase 1 LANE. Data direct VCC(s) do not offer any type of QoS guarantee, so they typically are used for UBR and ABR connections.

DATA ENCRYPTION STANDARD (DES):

A 56 bit key cryptographic algorithm: Endorsed by the National Bureau of Standards (NBS) for the encryption of data.

DATA ENTRY:

A term that may be used in different ways, but normally refers to computer system data input for processing.

DATA FLOW:

Grouping of traffic: Identified by a combination of source address/mask, destination address/mask, IP next protocol field, and source and destination ports, where the protocol and port fields can have the any appropriate value. In effect, all traffic matching a specific combination of these values is grouped logically together into a data flow.
A data flow can represent a single TCP connection between two hosts, or it can represent all the traffic between two subnets.

DATA FLOW CONTROL LAYER:

Layer 5 of the SNA architectural model: This layer determines and manages interactions between session partners, particularly data flow.

DATAGRAM:

A capability in a packet-switched network where a complete message may be contained in the data field of a packet, although not usually implemented on today's packet data networks (PDN).

DATA INTEGRITY:

Usually refers to the performance of a data communications system, ideally data transfers without errors.

DATA LINE INTERFACE:

PBX term for a point at which a data station can be connected to wiring

DATA LINE OCCUPIED:

A signal generated by a sensing circuit in an Automatic Calling Unit (ACU) that indicates to the computer that the requested line is not available.

DATA LINE PRIVACY:

A line exclusion function provided on data and fax lines to prevent noises from other users who may pick up the line during facsimile or data transmission use.

DATA LINK:

Electrical-mechanical communications line and equipment necessary to connect two or more devices; or an information communication channel, normally wideband and digitized.

DATA LINK CONTROL:

The management of transmitted data over communications circuits using appropriate controls, protocols, hardware and related software.

DATA-LINK CONTROL LAYER:

Layer 2 in the SNA architectural model: Responsible for the transmission of data over a particular physical link.

DATA LINK LAYER:

The second layer (Layer 2) in the Open Systems Interconnection (OSI) model that establish, maintains and releases data link connections between the network layer and physical layer. The data link layer is also responsible for error detection, transmission and reception of data-grams, packet reception and local addressing.

DATA-LINK SWITCHING (DLSw):

Interoperability standard, described in RFC 1434, that provides a method for forwarding SNA and NetBIOS traffic over TCP/IP networks using data-link layer switching and encapsulation. DLSw uses SSP instead of SRB, eliminating the major limitations of SRB, including hop-count limits, broadcast and unnecessary traffic, timeouts, lack of flow control, and lack of prioritization schemes.

DATA-LINK SWITCHING PLUS (DLSW+):

Cisco implementation of the DLSw standard for SNA and NetBIOS traffic forwarding function: DLSw+ goes beyond the standard to include the advanced features of the current Cisco RSRB implementation, and provides additional functionality to increase data-link switching capability.

DATA MART:

A repository of data, often a scaled down data warehouse, usually tailored to the needs of a specific group within an organization

DATA MESSAGE:

Information in a format, which can be computer or device processed for delivery to a specified destination. See Message

DATA MINING:

Using advanced statistical tools to identify commercially useful patterns in databases.

DATA MODE:

A term used to indicate the ready status of a Data Service Unit (DSU) or MODEM Request To Send and Data Set Ready circuits.

DATA MODEM:

A MODEM for data (digital to analog) that normally would not have the ability to send or receive only analog signals, such as fax transmissions.

DATA MOVEMENT PROCESSOR (DMP):

Processor on the Catalyst 5000 in combination with the multi-port packet buffer memory interface performs the frame-switching function for the switch. The DMP also handles translational bridging between the Ethernet and FDDI interfaces, IP segmentation, and intelligent bridging with protocol-based filtering.

DATA NETWORK:

A telecommunications system consisting of a number of connected terminals/computers able to automatically access each other via communication lines.

DATA NETWORK IDENTIFICATION CODE:

See DNIC

DATA OVER VOICE (DOV):

A Frequency Division Multiplexing (FDM) feature: Allows for the combination of voice and data on the same line. DOV usually employs twisted pair cables assigning some of the unused bandwidth for data transmission.

DATA PBX:

Private Branch Exchange (data) – A switching matrix that permits a user on an attached circuit to select other circuits for the purpose of establishing a through connection. Only digital transmission is supported.

DATAPHONE DATA SET:

An AT&T Data Set, which is used for transmission of data over the telephone network.

DATAPHONE DIGITAL SERVICE (DDS):

An AT&T private line service for transmitting data over a digital system; the digital technique allows for more efficient use of the transmission facilities, since a MODEM isn’t required, resulting in lower error rates and costs than with analog systems. AT&T filed for DDS with the FCC in 1974.

DATA PORT

The point of access (interface) to a computer for sending or receiving data

DATA QUALITY MONITOR:

See DQM

DATA RATE:

See Data Transfer Rate

DATA SERVICE UNIT (DSU):

A MODEM replacement device used in a digital network, the DSU provides for remote and local testing, loop equalization and the electronics needed to provide a standard Electronic Industries Association (EIA) or Consultative Committee International telegraph and Telephone (CCITT) interface. DSU's may have an associated integrated Channel Service Unit (CSU).

DATA SET (DS):

A device: Converts digital data into analog signals for transmission over telecommunication lines. The term ‘MODEM’ commonly used by computer communications personnel has a much broader range of application in general telecommunications.

DATA SET ADAPTER:

An interconnection device located in terminal or computer equipment, which provides various controls and features and interfaces the Data Set and in some cases may replace the Data Set.

DATA SET READY (DSR):

An RS232 (x) signal: Indicates the MODEM is on and ready to accept input from the distant end.

DATA SIGNAL RATE SELECT (Signaling Rate Selector):

A RS-449 (Pin 16) - Data transmission speed control signal; change speed request.

DATA SINK:

A device that can accept data signals from a transmission device.

DATA STREAM:

The transmission of information bits or characters over a channel (line)

DATA SWITCH:

An electrical/mechanical switch used to connect data processing equipment to network lines.

DATA SYSTEMS ANALYST, INC.:

See DSA, Inc.

DATA TERMINAL (DT):

A station (terminal) in a system capable of sending and/or receiving data (messages)

DATA TERMINAL EQUIPMENT (DTE):

A term used to describe data processing and connection equipment such as computers, terminals, controllers, interfaces and printers.

DATA TERMINAL INTERFACE (DTI):

The connection and/or control point between a data terminal and telephone (analog) system.

DATA TERMINAL READY (DTR):

A RS232 (X) signal sent from the computer to the MODEM indicating the computer is ready to communicate.

DATA TERMINAL SUBSET:

Another name for Data Set or Data Set Adapter

DATA TRANSFER FACILITY (DTF):

A device that provides bi-directional data transfer between an IBM MVS system in a System Network Architecture (SNA) environment and VAX/VMS systems in a DECnet network.

DATA TRANSFER RATE:

Usually refers to a line or channel data transmission capability. Many factors dictate the actual data transfer rate (speed) capability, such as the following:

1) MODEM designated bit speed rate

2) The condition or quality of the Line (channel). Dial up lines (unless conditioned) will vary because the lines accessed will change with each call.

3) Local connection (twisted pair, etc.) to the telephone Company or vendor.

4) Communications equipment servicing the line or MODEM

5) Computer equipment, locally, intermediate and distant

On average a 56K MODEM will probably function at a 28K to 30K bps rate due to the errors (distortion) caused by line and equipment conditions.

DATA TRANSMISSION:

The process of sending data from one location to another over a channel (circuit)

DATA UNDER VOICE:

See DUV

DATA WAREHOUSE:

A very large repository of data; a company’s information storage

DATABASE OBJECT:

A piece of information that is stored in a database

DATAGRAM:

Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP data-grams are the primary information units in the Internet. The terms cell, frame, message, packet and segment and also are used to describe logical information groupings.

DATAKIT:

AT&T proprietary packet switching system

DATAPHONE:

An AT&T trademark identifying a type of communications equipment for data communication service

DATAPHONE DIGITAL SERVICE (DDS):

An AT&T communications service: The data is transmitted in digital format rather than analog form; eliminates the need for a MODEM.

DATASPEED:

An AT&T term used to identify a variety of data communications devices.

DATASPEED SERVICE:

An original AT&T teletypewriter and business machine data transmission service over the telephone network at speeds up to 1200 Words per Minute (WPM)

DAVIC:

Digital Audiovisual Council: Now defunct, was established in 1994 with the aim of promoting the success of interactive digital audio-visual applications and services.

DATUM:

(1) A theoretically exact point, axis, or plane derived from the true geometric counterpart of a specific datum feature.

(2) The origin from which the location or geometric characteristics or features of a part are established

(3) Calculated information

D BIT:

Delivery Confirmation Bit: A bit used in the Consultative Committee International Telegraph and Telephone (CCITT) X.25 packet switching networks to request end to end acknowledgment.

D-CONDITIONING:

A common carrier service designed to control the harmonic distortion and improve the signal-to-noise ratio. D-conditioning is currently being offered in 9600 bps service.

DB CONNECTOR:

Data Bus Connector: Type of connector used to connect serial and parallel cables to a data bus. DB connector names are in the format DB-x, where x represents the number of wires within the connector. Each line is connected to a pin on the connector, but in many cases, not all pins are assigned a function. DB connectors are defined by various EIA/TIA standards.

dB:

   Decibel:  A logarithmic measurement of acoustic or electrical power, voltage, or current ratios; sometimes used in reference to noise or interference. Units are expressed in terms of the logarithm to base 10 of a ratio and typically are expressed in watts. dB is not an absolute value, rather it is the measure of power lost or gained between two devices. For example, a -3dB loss indicates a 50% loss in power; a +3dB reading is a doubling of power. The rule of thumb to remember is that 10 dB indicates an increase (or a loss) by a factor of 10; 20 dB indicates an increase (or a loss) of a factor of 100; 30 dB indicates an increase (or a loss) by a factor of 1000. 

   In fiber optics, a unit used as a logarithmic measure to describe the attenuation (optical power loss per unit length) in a fiber

DBA:

Data Base Administrator

dBA:

A noise measurement unit

DB/DC systems:

Database/Data communications systems

DBi:

dB referenced to an isotropic antenna, which theoretically is perfect in terms of symmetric patterns of radiation. Real world antennas do not perform with even nominal amounts of symmetry, but this reference is basically used by system designers.

dBm:

Decibels per milliwatt: 0 dBm is defined as 1 mw at 1 kHz (kilohertz) of frequency at 600 ohms of impedance.

dBmO: Noise power in dbm at a point of zero relative transmission level

DBMS:

Data Base Management System

DBmV:

Decibels with respect to one millivolt in a 75-ohm system: The measurement unit of Radio Frequency (RF) power used for CATV purposes in North America.

dBr:

Decibels Level Reference

DB2:

Data-Base 2: IBM database management system

Dbw:

dB referencing 1 watt

DC1, DC2, DC3, DC4:

ASCII control characters used for controlling ancillary devices associated with data processing, telecommunication systems or switching devices, I.E. start, pause, and stop, on or off.

DC:

See Direct Current

DCA:

Defense Communications Agency: Government organization responsible for DDN (Defense Department Networks), such as MILNET (Military Network); now called DISA (Defense Information Systems Agency).

DCC:

1) Data Communications Channel: Channel that carries provisioning and maintenance data/information between network elements in the SONET environment.

2) Data Country Code: One of two ATM address formats developed by the ATM Forum for use by private networks. Adapted from the sub-network model of addressing in which the ATM layer is responsible for mapping network layer addresses to ATM addresses.

DCCU:

Data Communications Control Unit

DCD:

Data Carrier Detect or Data Collection Device

DCE:

1) Data Communication Equipment: A configuration protocol identifying the type of data connection used for equipment that connects to a communications facility. Example: Interconnecting RS-449, RS-232, V.35, X.21 and other digital communications signals.

2) Data Circuit Terminating Equipment (Example: MODEM): Communications equipment responsible for establishing, maintaining and terminating a connection. See DTE

3) RS-449 DCE Ready signal (Pin 13A & 31B): Indicates the DCE is in an operational mode.

4) Data Circuit-Terminating Equipment (ITU-T expansion): Devices and connections of a communications network that comprise the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE (Data Terminal Equipment) devices.

DCF:

Dispersion Compensating Fiber: A fiber that has the opposite dispersion of the fiber being used in a transmission system and is used to nullify the dispersion caused by the other fiber.

DCI:

Dual Communications Interface: An interface that allows simultaneous transmission of the two halves of a set of communications data over two similar communications interfaces. The most common application is for connection using two switched 56 Kbps transmission circuits or an ISDN-BRI (2B+D).

DCN:

Data Communications Network:

1) Communication links (circuits/lines) connecting various devices allowing commonly shared network services.

2) In an Operations Support System (OSS); provides connectivity between network elements and their respective operations support systems. Its primary function is enabling the surveillance and the status of a Telco/PTT network but it also facilitates network operations and management, such as provisioning, billing, planning, and service assurance.

DCOM:

Distributed Component Object Model: Protocol that enables software components to communicate directly over a network. Developed by Microsoft and previously called Network OLE, DCOM is designed for use across multiple network transports, including such Internet protocols as HTTP.

DCR:

See Dynamically Controlled Routing

DCS:

1) Defense Communications System.

2) Digital Cross-connect System: A type of high-speed data channel switch that switches transmission paths in response to dialing instructions.

DCT:

Data Communications Terminal or Discrete Cosine Transform

DDCMP:

Digital Data Communications Message Protocol: A defined protocol for transmission of data between stations (terminals) in a point-to- point or multi-point data communications system, with parallel, serial synchronous, or serial asynchronous data transfer.

DDD:

Direct Distance Dialing: Refers to the North American telephone dial system, which enables telephone users to call other users outside the local area without operator assistance. In the United Kingdom and some other countries, the service is known as STD (Subscriber Trunk Dialing).

DDIC:

DVB/DAVIC Interoperability Consortium: Founded in October 1998 by an international group of manufacturers, including Cisco, the Consortium promotes and supports product interoperability between member vendors employing the DVB-RCCL/DAVIC international standards.

DDM:

Distributed Data Management: Software in an IBM SNA environment that provides peer-to-peer communication and file sharing

DDN:

1) Defense Digital Network: Digital packet switching networks meeting data communications requirements of the Department of Defense.

2) Defense Data Network: U.S. Military Network (MILNET) composed of an unclassified network and various secret and top-secret networks.

DDP:

Datagram Delivery Protocol: AppleTalk network layer protocol that is responsible for the socket-to-socket delivery of data-grams over an AppleTalk inter-network.

DDR:

Dial-on-Demand Routing: Technique where a router can automatically initiate and close a circuit-switched session based on transmitting stations demand.

DDS:

1) Data-phone Digital Service: An AT&T communications service, in which data is transmitted in digital rather than analog form, thus eliminating the need for MODEMs.

2) Digital Data Service: A synchronized data-communications network formed by inter-connecting digital transmission facilities. DDS normally operates at 2.4, 4.8, 9.6, or 56 Kbps.

DDS TEST UNIT (DTU):

The Hekimian Model 6302 test set that provides bi-directional DS1 and DS0A/DS0B interfaces. These interfaces are required for T1 and sub-rate access and testing.

DDSN:

Distributed Diagnostics and Service Network: Facilities that gather events within the ICM and automatically report any unexpected behavior to Cisco Customer Support: The DDSN includes the Customer Support Forwarding Service (CSFS) and the DDSN Transfer Process (DTP).

DDSIII:

Defense Dissemination System Phase III: Disseminates digital imagery to strategic and tactical commanders; consists of high- and low-rate data circuits.

DE:

Discard Eligible: If a network is congested, DE traffic can be dropped to ensure the delivery of higher priority traffic.

DEA:

Data Encryption Algorithm: Symmetric block cipher, defined as part of the U.S. Government's Data Encryption Standard. DEA uses a 64-bit key, of which 56 bits are independently chosen and 8 are parity bits, and maps a 64-bit block into another 64-bit block.

DE-ACTIVATION:

Process of disabling network access and privileges for a subscriber device; de-activation occurs as part of subscriber account de-provisioning, or as part of activation of a replacement subscriber device; some device attributes (such as IP address leases) might not be reclaimable until the leases have expired.

DEADLOCK:

1. Unresolved contention for the use of a resource.

2. In APPN, when two elements of a process each wait for action by or a response from the other before they resume the process.

DEBUGGING:

A process of detecting and correcting computer hardware or software malfunctions and/or errors

DECCO:

Defense Commercial Communications Office; A Department of Defense organization that procures communications circuits from carriers for use by the military and certain other federal agencies.

DEC:

Digital Equipment Corporation (Digital)

DECENTRALIZED:

A form of ’Remote Processing’ - A systems processing method where common shared information is located and processed at different remote locations.

DECIBEL (DeciBel):

See dB.

DECIMAL:

The term refers to a digital (number) system that has ten possible states, 0 through 9.

DECK:

A stack of punched cards, which have been punched for a specific service or purpose

DECNET (DECnet):

A Digital Equipment Corporation (DEC) networks system that permits inter connection of DEC computers using Digital Data Communications Message Protocol (DDCMP).

DECnet/OSI (DECnet Phase V) is the most recent product and supports both OSI (Open System Interconnection) protocols and proprietary Digital protocols.

DECnet ROUTING:

Proprietary routing scheme introduced by Digital Equipment Corporation in DECnet Phase III. In DECnet Phase V, DECnet completed its transition to OSI routing protocols (ES-IS and IS-IS).

DECODE:

To determine the meaning of individual or groups of characters in a message or determine the meaning of an instruction from a set of pulses (bits), which describe the instruction, command or operation to be performed; could also refer to encryption and de-encryption.

DECRYPTION:

The opposite of ‘Encryption’: Encryption is the process of changing data into a form that can be read only by the intended receiver. To decipher the message, the receiver of the encrypted data must have the proper decryption key. In traditional encryption schemes, the sender and the receiver use the same key to encrypt and decrypt data. See System Security

DEDICATED DATA CHANNEL:

A data channel or circuit dedicated for the private use of a particular customer.

DEDICATED LAN:

Network segment allocated to a single device. Used in LAN (Local Area Network) switched network topologies.

DEDICATED LINE:

A user assigned circuit that is dedicated to data transmission between two locations; also referred to as a leased line or private line. Communications line that is indefinitely reserved for transmissions, rather than switched as transmission is required.

DEDICATED SERVICE:

A telecommunications service provided to a subscribing customer for their exclusive use.

DE FACTO STANDARD:

A Standard that exists by nature of its widespread use

DEFAULT PASSWORD:

A password within a system when it is first delivered or installed

DEFAULT ROUTE:

Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table.

DEFAULT USER:

The profile that serves as a basis for all user profiles: Every user profile begins as a copy of the default user profile.

DEFENSE ADVANCED RESEARCH PROJECTS AGENCY (DARPA):

Formerly ARPA: A US government agency that funds research, experimentation and implementation of the Government Internet network. The ISTO (Information Systems Techniques Office) group within DARPA is responsible for the ARPAnet, formerly IPTO (Information Processing Techniques Office).

DEFRAG:

To improve file access by rearranging data so that whole files are stored in contiguous sectors on a hard disk.

DEFRAGMENTATION:

The process of rewriting parts of a file to contiguous sectors on a hard disk to increase the speed of access and retrieval: When files are updated, the computer tends to save these updates on the largest continuous space on the hard disk, which is often on a different sector than the other parts of the file. When files are fragmented, the computer must search the hard disk each time the file is opened to find all of the file parts, which slows down response time.

DEGRADED MINUTE:

References a minute of data transfer to be degraded if it has all SES removed and has more than 93 CRC-6 violations or 93 frame bit errors.

DEGRADATION:

Refers to a condition where the system continues to operate, but at a reduced level of speed or service. Unavailability of equipment subsystems or components and degradation of facilities are the usual cause.

DE JURE STANDARD:

Standard that exists because of its approval by an official standards body

DEK:

Data Encryption Key: Used for the encryption of message text and for the computation of message integrity checks (signatures).

DEL:

‘Delete’: A character used primarily to erase or obliterate erroneous or unwanted characters in perforated tape or may be used as fill (spacing) characters between messages.

DELAY:

The time between the initiation of a transaction by a sender and the subsequent response received by the sender; also, the time required to move a packet from source to destination over a given path.

DELAY:

1) The time interval between the time a signal is sent and the time it is received.

2) The time between the initiation of a transaction by a sender and the subsequent response received by the sender (Inquiry – Response)

3) In packet switching, the additional time introduced by the network in delivering a packet compared to the time the same information would take on a full-period point-to-point circuit

DELAY DISTORTION:

An unwanted change in transmitted digital or analog signals due to the non-uniform speed of transmission

DELAY EQUALIZER:

A device that corrects delay distortion by making the delay fairly constant over a pre-determined frequency range

DELIVERY TIME:

In communications it would be a measurement of delivery time from the start of a transmission to the end of reception at the receiving terminal.

DEMAND PRIORTY:

Media access method used in 100VG-AnyLAN that uses a hub that can handle multiple transmission requests and can process traffic according to priority; making it useful for servicing time-sensitive traffic, such as multimedia and video. Demand priority eliminates the overhead of packet collisions and collision recovery.

DEMARC:

Demarcation point between carrier equipment and Customer Provided Equipment (CPE)

DEMODULATION:

Demodulation is the process of transforming an analog signal into digital data, for instance, when data is transferred over phone lines, a MODEM ‘modulates’ the data into audible tones ‘carried’ within frequencies between 0 Hz and 4 KHz. Once the data reaches its intended destination, another MODEM ‘demodulates’ the signal back into digital data. Cable TV networks also use modulation techniques to transfer data. But instead of audible tones, cable has sophisticated digital modulation schemes that greatly increase the amount of data that can be sent in a given period of time.

DEMODULATOR:

The demodulation part of a MODEM where the received analog line signals are converted back to digital form

DEMULTIPLEXING:

The opposite of multiplexing where a composite signal is broken into component channels

DEMUX:

De-multiplex: The opposite of multiplexing (combining) where a composite signal is broken into component channels. Device used to separate two or more signals that previously were combined by a compatible multiplexer and are transmitted over a single channel (line).

DENIAL OF SERVICE (DOS):

An attack specifically designed to prevent the normal functioning of a system and thereby to prevent lawful access to the system by authorized users. Hackers can cause denial of service attacks by destroying or modifying data or by overloading the system's servers until service to authorized users is delayed or prevented.

DEPROVISIONING:

Elimination of an existing subscriber account; de-provisioning of a subscriber account includes subscriber account de-registration and device de-activation.

DER:

Distinguished Encoding Rules: A subset of the Basic Encoding Rules; gives exactly one way to represent any ASN.1 value as an octet string [X690]

DERIVED FACILITY/DERIVED FACILITIES:

Transmission paths created through the use of multiplexing to provide more than one virtual path per physical facility.

DES:

1) Data Encryption Standard: A 64-bit private-key encryption technique; an encryption encoding system that provides security and ‘privacy’ of data communication, making unwanted interception and decoding basically impossible.

2) Destination End Station.

DESIGNED BRIDGE:

Bridge that incurs the lowest path cost when forwarding a frame from a segment to the root bridge.

DESIGNED ROUTER:

OSPF router that generates LSA(s) for a multi-access network and has other special responsibilities in running OSPF: This designated router enables a reduction in the number of adjacencies required on a multi-access network, which in turn reduces the amount of routing protocol traffic and the size of the topological database.

DESKTOP:

The on-screen work area on which windows, icons, menus, and dialog boxes appear.

DESKTOP PATTERN:

Screen Saver: A design that appears across the desktop screen. You can create your own pattern or select a pattern provided by the operating system (Windows).

DESTINATION:

Communications: Normally the addressee identified in the address field of a message.

DESTINATION ADDRESS:

The part of a message (header), usually a collection of characters or bits, that indicates for whom the message is intended (addressee).

DESTINATION ADDRESS(s) FILTERING:

A feature involving bridges: Only messages intended for nodes on the extended local area network (LAN) are forwarded.

DESTINATION DOCUMENT:

The document into which a package or a linked or embedded object is being inserted: An embedded object is sometimes called the container document.

DESTINATION FIELD:

The field in a message header that contains the network address of the destination (person) to whom the message is being sent.

DESTINATION NODE:

Termination (connection) of an end-to-end channel or Virtual Wavelength Path (VWP)

DETERMINISTIC LOAD DISTRIBUTION:

Technique for distributing traffic between two bridges across a circuit group: Guarantees the order of packets between source-destination pairs and always forwards traffic for a source-destination pair on the same segment in a circuit group.

DEVICE:

Any piece of equipment that can be attached to a network or computer: A computer subsystem such as a printer, serial port, disk drive, MODEM or video adapter. Frequently, devices require their own controlling software (device drivers) to communicate with the computer system.

DEVICE DRIVER:

A program that allows a specific device, such as a MODEM, network adapter, or printer, to communicate with the operating system: Although a device might be installed on or connected to the system, the operating system (Windows) cannot use the device until an appropriate driver has been installed and configured. If a device is listed in the Hardware Compatibility List (HCL), a driver is usually included with Windows. Enabled device drivers load automatically when a computer is started.

DEVICE FONTS:

Fonts that reside (stored) in the printer. They can be built into the printer itself or provided by a font cartridge or font card.

DEVICE MANAGER:

An administrative tool that can be used to manage the devices on the computer: Using Device Manager, an individual can view and change device properties, update device drivers, configure device settings, and uninstall devices.

D4/D-4:

A data transmission format composed of 12 frames consisting of 192 bits each. A single 193rd bit is used for link control and error checking. D-4, also known as SF, has been superseded by the ESF format as the industry standard.

D4 FRAMING:

Super Frame, common framing type used on T1 circuits: SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF was superseded by ESF, but is still widely used.

DGMS:

A computer software development company founded by John Dale, Bill Gesek, Rex McWilliams and Bill Sheridan; See DSA, Inc

D-H:

Diffie-Hellman: The Diffie-Hellman algorithm, introduced by Whitfield Diffie and Martin Hellman in 1976, was the first system to utilize ‘public-key’ or ‘asymmetric’ cryptographic keys. Today Diffie-Hellman is part of the Internet Protocol Security (IPSec) standard.

DHCP:

Dynamic Host Configuration Protocol: Provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when the host no longer needs them. Lets a network administrator supervise and distribute Internet Protocol (IP) addresses from a central point, and automatically send a new address when a new computer is connected to the network.

DHTML:

Dynamic HTML - DHTML makes Web pages seem more like applications or multimedia interfaces by using Java-Script, VB-Script, ActiveX, Cascading Style Sheets (CSS) and other technologies to run programs locally, instead of interacting remotely with the server providing the page.

DIA:

Document Interchange Architecture: Defines the protocols and the data formats needed for the transparent interchange of documents in an SNA network.

DIAGNOSTIC / DIAGNOSTIC PROGRAM:

   There are two basic types of computer diagnostics.

1) Software diagnostic - Programmers use software diagnostics to detect, analyze, isolate and fix computer program bugs (problems). For example, the insertion of a software diagnostic program ‘patch’ in a suspected (problem) area of a program to isolate a problem. When the patch containing the diagnostic instructions is encountered and executed, certain memory location addresses and pre-determined ‘flags’ would be output and displayed for review by the software personnel. It would not be necessary to halt the computer during this process. A ‘halt instruction’ patch (break point) strategically placed in a suspected area of a failing software program undergoing debugging would stop the computer. This allows the programmer to examine the internal registers and other areas while the computer is not cycling.

2) Hardware diagnostic - A computer software program designed to perform a series of routine hardware tests. Basically, the computer that is executing the diagnostic would be performing a self-introspection of itself. These routine tests are called ‘exercisers’ and are designed to stimulate the computer hardware. If the diagnostic exerciser detects an error condition in the hardware under test, it would then call in a series of ‘diagnostic’ programs that would systematically apply known test patterns to isolate the failed component.

   Hardware diagnostic systems follow a basic sequence of steps:

1) Exercise the hardware in a logical sequence (increasing complexity)
2) Detect the fault
3) Diagnose the fault
4) Analyze the fault (compare the input stimulus against the output response).
5) Isolate the fault (reduce comparisons to the most likely components’)
6) Physically locate the fault (circuit card(s) physical location)
7) Display the diagnostic results (repair action)

DIAL BACKUP:

A feature that provides protection against WAN downtime by allowing the network administrator to configure a backup serial line through a circuit-switched connection

DIAL LINE / DIAL UP LINE:

Refers to a dial up or dial in line, basically any communications line that must be dialed to make a connection.

DIAL NETWORK:

Could be a private or public dial network, but usually refers to the public telephone network.

DIAL PEER:

Addressable call endpoint: In Voice over IP, there are two kinds of dial peers: POTS and VoIP.

DIAL-UP CONNECTION:

A connection process for connecting to a network using a device that connects through the telephone network. This includes a MODEM using a standard telephone line, ISDN (Integrated Services Digital Network) cards with high-speed ISDN lines, or X.25 networks.

DIALOG BOX:

A secondary window that contains buttons and various kinds of options through which an individual can carry out a particular command or task.

DIBIT:

A group of two bits in four-phase carrier modulation, each possible dibit is encoded as one of four unique carrier phase shifts. The four possible states for a dibit are 00, 01, 10 and 11.

DICTIONARY ATTACK:

A method of determining a user's password or PIN by trying every word in the dictionary until successful.

DID:

Direct Inward Dial: Allows a user outside a company to dial an internal extension number without needing to pass through an operator or an attendant. The dialed digits are passed directly to the PBX, which then completes the call.

DID/DNIS:

Direct Inward Dialing / Dialed Number Identification Service: When a call arrives at an ACD or PBX, the carrier sends a digital code on the trunk line. The switch can read this code to determine how it should dispatch the call. Typically, this value is the specific number dialed by the user.

DIFFERENTIAL ENCODING:

Digital encoding technique where 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 beginning of each bit time denotes a zero. This coding scheme is used by IEEE 802.5 and Token Ring networks.

DIFFERENTIAL PHASE SHIFT KEYING (DPSK):

Modulation process: Used in the Bell 201 MODEM. See Dibit

DIFFERENTIATED SERVICE:

   Functional procedures for providing QoS (Quality of Service) on the Internet by employing a small, well-defined set of building blocks from which a variety of services can be built

   At present, all packets on the Internet are treated in the same manner, regardless of their importance. If an important message needs to be delivered immediately or a streaming video signal needs to be distributed smoothly and without interruptions, there is no way to differentiate between high priority needs and routine transmissions, which could cause delays. There are currently efforts under way to test and develop standards for differentiated services, where high priority data can be sent through or around clogged nodes ahead of low priority data.

Diffie-Hellman KEY EXCHANGE:

A public key cryptography protocol that allows two parties to establish a shared secret over insecure communications channels: Diffie-Hellman is used within Internet Key Exchange (IKE) to establish session keys.

DIFFUSING UPDATE ALGORITHM:

Convergence algorithm used in Enhanced IGRP that provides loop-free operation at every instant throughout a route computation. Allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change.

DIGERATI:

The digital version of literati, it is a reference to a vague cloud of people seen to be knowledgeable, hip, or otherwise in-the-know in regards to the digital revolution.

DIGIT, DIGITAL:

A discretely variable signal as compared with analog, which is continuously variable; data signals are coded in discrete and separate pulses, DC ‘pulse’ signals, bits, 1 or 0, not an analog signal

DIGITAL:

(Digital Equipment Corporation - DEC)

DIGITAL CERTIFICATE:

Certificate document in the form of a digital data object (computer data object) to which a computed digital signature value that depends on the data object is added.

DIGITAL DATA:

Information represented by digital code (bits).

DIGITAL ENVELOPE:

Digital envelope for a recipient is a combination of (a) encrypted content data (any kind) and (b) the pre-prepared recipient content encryption key in an encrypted form.

DIGITAL ERROR:

Digital transmission where a bit is gained or lost due to line or device problems; a 1 bit is dropped, becomes a 0, or a 0 bit becomes a 1.

DIGITAL INFORMATION SIGNAL:

T.30 Digital Information Signal that provides the functional capabilities of a receiving fax machine.

DIGITAL LOOPBACK (DLB):

Testing method in which received data is fed back to the transmitting source without processing; used to isolate circuit problems.

DIGITAL MULTIPLEXED INTERFACE:

See DMI

DIGITAL NERVOUS SYSTEM (DNS):

A term used by Bill Gates in frequent speeches in 1997 and 2000. Gates describes a future merging of PCs and communications in a wireless networked environment that makes it easy for people to navigate and share information.

DIGITAL NETWORK ARCHITECTURE (DNA):

The data network architecture of Digital Equipment Corporation (DEC)

DIGITAL SERVICE UNIT:

1) A network interface device between a Channel Service Unit (CSU) and the Data Terminal Equipment (DTE). The DSU utilizes a V.35, RS232, RS449 connection protocol, or other possible interfaces. The DSU can also function as a multiplexer for FT1 circuits.

2) A PC type of terminal for local area networks (LANs), without disk drives, boots its operating system from the server and processes assigned tasks in a client/server network environment.

DIGITAL SIGNALS:

In a digital environment, the analog sound wave (Hz) is converted into a digital signal (zeros and ones) through Modulation schemes. The digital representation of the voice or data is similar to how Morse code used dots and dashes to transmit conversation.

All electrical signals, whatever their type, lose strength and quality over distances due to noise or other extraneous factors. Digital signals, however, have one distinct advantage over their analog equivalent. Analog signals must be amplified, noise and all, to be transmitted over long distances. Digital signals are repeated or regenerated and new error-free signals are forwarded. The repeater recognizes the distorted signal and reconstructs the original sequence of zeros and ones. The repeater then reproduces the signal and sends it to the next destination in the network. With digital transmission data traveling 10 miles or 3,000 miles will share the same quality

DIGITAL SIGNAL CROSS-CONNECT LEVEL 1:

See DSX-1

DIGITAL SIGNAL LEVEL 1C:

See DS-1C

DIGITAL SIGNAL LEVEL 2:

See DS-2

DIGITAL SIGNATURE:

   Value computed with a cryptographic algorithm and appended to a data object in manner that any recipient of the data can use the signature to verify the data origin and integrity.

   A process for originators of a message, file, or other digitally encoded information, to bind their identity to the information. The process of digitally signing information entails transforming the information, as well as some secret information held by the sender, into a tag called a signature. Digital signatures are used in public key environments and they provide integrity services.

DIGITAL SUBSCRIBER LINE (DSL):

A type of high-speed Internet connection using standard telephone wires (facilities). This is also referred to as a broadband connection.

DIGITAL SUBSCRIBER LINE ACCESS (DSLAM):

See DSLAM

DIGITAL VIDEO DISC ‘DISK’ (DVD):

A type of optical disc storage technology: A digital video disc (DVD) looks like a CD-ROM disc, but it can store greater amounts of data. DVDs are often used to store full-length movies and other multimedia content that requires large amounts of storage space.

DIGITAL SWITCHING:

A process where a connection is established and Digital information is routed between input and output.

DIGITAL TERMINATION SYSTEM:

See DTS

DIGITAL TRANSMISSION (Digital Data):

Refers to information (data) represented by discrete pulses (DC-bits), not analog (AC) signals.

DIGITAL SWITCHING:

A process in which circuit connections are established based on digital signals without converting them to analog signals.

DIGITIZE:

To convert an analog or variable level signal into a numerical value or digital binary bit form.

DIN:

Deutsche Industrie Norm: German national standards organization

DIN CONNECTOR:

Deutsche Industrie Norm Connector: Multi-pin connector used in some Macintosh and IBM PC-compatible computers and on some network processor panels.

DINAH:

Desktop Interface-to-AUTODIN Host

DIODE:

An electrical component that permits a current flow in one direction and inhibits current flow in the opposite direction

DIP:

Dual In line Pins or Dual In line Package: A term used to identify an electronic component package, Integrated Circuit ‘Chip’, and/or the fact the connector end has two rows of connecting pins.

DIP SWITCH:

Usually refers to a switch matrix with the physical characteristics of a Dual In line Package (DIP).

DIRECT ACTION VIRUS:

A direct action virus works immediately to load itself into memory, infect other files, and then to unload itself.

DIRECT CABLE CONNECTION:

A link between the I/O (Input/Output) ports of two computers created with a single cable rather than a MODEM or other interfacing devices.

DIRECT CONNECTION:

A connection made directly to the Internet, usually faster than a dial-up connection.

DIRECT CURRENT (DC):

Electrical current that flows in one direction only, from positive (+) to negative (-) in a circuit

DIRECT CURRENT LOOP:

Current Loop, Local Loop or Loop – The connection between the line and a terminal device, terminal interface, and Direct Current (DC) digital signal is used. A MODEM may or may not be used.

DIRECT DISTANCE DIALING:

See DDD

DIRECT INWARD DIALING (DID):

Usually refers to a PBX function where a telephone caller is able to call directly into an internal extension without operator assistance.

Calls in which the gateway uses the number initially dialed (DNIS) to make the call, as opposed to a prompt to dial additional digits. See DID

DIRECT MEMORY ACCESS:

See DMA

DIRECT OUTWARD DIALING (DOD):

Usually refers to a PBX function where an internal extension (caller) is able to call an external number without operator assistance.

DIRECTED SEARCH:

Search request sent to a specific node known to contain a resource. A directed search is used to determine the continued existence of the resource and to obtain routing information specific to the appropriate node.

DIRECTED TREE:

Logical construction used to define data streams or flows. The origin of a data stream is the root. Data streams are unidirectional branches directed away from the root and toward targets, and targets are the leaves of the tree.

DIRECTORY ENABLED NETWORKING:

An LDAP-based information model for networked devices

DIRECTORY PARTITION:

   A contiguous sub-tree of the directory that forms a unit of replication: A given replica is always a replica of some directory partition. The directory always has at least three directory partitions:

1) The scheme (schema), which defines the object classes and attributes contained in the Active Directory.

2) The configuration, which identifies the domain controllers, replication topology and other related information about the domain controllers within a specific part of the Active Directory.

3) One or more domains that contain the actual directory object data.

   A domain controller always stores the partitions for the schema, configuration, and its own domain. The schema and configuration are replicated to every domain controller in the domain tree or forest. The domain is replicated only to domain controllers for that domain. A subset of the attributes for all domain objects is replicated to the global catalog.

DIRECTX:

An extension of the Microsoft Windows operating system: DirectX technology enables games and other programs to use the advanced multimedia capabilities of the hardware.

DIS:

Defense Information Service

DISA:

Defense Information Systems Agency: An agency within DoD responsible for the overall operational management and control of DMS.

DISANMOC:

Defense Information Systems Agency Network Management and Operations Center

DISASTER RECOVERY:

Preventative measures using redundant hardware, software, data centers and other facilities to ensure that a business can continue operations during a natural or man-made disaster and if not, to restore business operations as quickly as possible when the failure has been resolved.

DISC:

Hard Disk Drive or other referenced disc (disk) drives or one disc platter within a disk drive, or used to reference a Disconnect Command (DISC).

DISCONNECT SIGNAL:

The signal transmitted from one end of a subscriber line or trunk to indicate to the other end that the established connection should be disconnected.

DISCOVERY ARCHITECTURE:

APPN software that enables a machine configured as an APPN EN to find primary and backup NN(s) automatically, when the machine is brought onto an APPN network

DISCOVERY MODE:

Method by which an AppleTalk interface acquires information about an attached network from an operational node; then uses this information to configure itself

DISCRETE ACCESS:

Refers to a Local Area Network (LAN), star topology, access method where each station is connected separately to maximize the LAN's switching capabilities.

DISENGAGE REQUEST:

A message with the Billing Information Token (contains call duration) sent by the gateway to the gatekeeper when a call ends.

DISINFECTION:

Most anti-virus software carries out disinfection after reporting the presence of a virus to the user. During disinfection, the virus may be removed from the system and, whenever possible, any affected data is recovered.

DISK CONTROLLER:

The hardware that controls the writing and reading of data to and from a disk drive: It can be hard-wired or built into a plug-in interface board (card).

DISK MIRRORING:

Disk mirroring provides the highest data availability for critical applications by creating two copies of data on separate disk drives. This technique ensures both the highest availability and highest system performance.

DISK OPERATING SYSTEM:

See DOS

DISK PROMPT:

A:\ xxxxxx(command): loads from ‘A’ drive and a function is performed.

Windows® 95 Examples:

 A:\ FORMAT C: /C /U. which causes drive ‘C’ to be formatted; Load from A drive.

C:\ COPY D:\Win95\*.*C:\Win95 which causes Windows 95 to be loaded; Load from D drive

DISK (DISC) STORAGE:

The function of storing data on the surface of a magnetic disk; often referred to as secondary storage. One or more flat circular discs with a magnetic surface (both sides) are used. A disk unit could have fixed heads or movable heads. See drum for additional information.

DISK STRIPING:

Combining a set of same-size disk partitions from 2 to 32 separate disks into a single volume that virtually ‘stripes’ these disks in such a way that the operating system recognizes them as a single drive. Disk striping enhances performance by enabling multiple I/O (Input/Output) operations in the same volume to proceed simultaneously.

DISK STRIPING with PARITY:

The use of parity (error) checks to preserve information across a disk stripe so that if one disk partition fails, its data can be re-created with information stored across the remaining portions of the disk stripe.

DISMOUNT:

To remove a removable tape or disc from a drive

DISN:

Defense Information Systems Network: DISA integrated the Defense Data Network (DDN) packet switching networks under the DISN. DISN provides DOD worldwide packet switched data communications through four physically separate networks. These networks were implemented with technology developed by the Advanced Research Projects Agency (ARPA) using packet switch nodes (PSN).

DISNET:

Defense Integrated Secure Network

DISOSS:

See Distributed Office Support System

DISPLAY ADAPTER:

Similar to Video Adapter: An expansion board that plugs into a personal computer to give it displaying capabilities. A computer's display capabilities depend on both the logical circuitry, provided in the video adapter, and the monitor. Each adapter offers several different video modes. The two basic categories of video modes are text and graphics. Within the text and graphics modes, some monitors also offer a choice of resolutions. At lower resolutions a monitor can display more colors.

Modern adapters contain memory, so that the computer RAM is not used for storing displays. In addition, most adapters have their own graphics co-processor for performing graphics calculations. These adapters are often called graphics accelerators.

DISPLAY UNIT:

A device that provides a visual representation of information or data

DISTANCE VECTOR ROUTING ALGORITHM:

A class of routing algorithms that iterate on the number of hops in a route required 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 link state routing algorithms.

DISTORTION:

Generally an unwanted, often a not predicted change in a transmission signal that renders the resulting output less than optimum; may result in error conditions.

1) An undesired change in a wave form or digital signal quality.

2) A nonlinear relation between input and output at a given frequency.

3) A non-uniform transmission at different frequencies.

4) A phase shift not proportional to the frequency.

DISTORTION DELAY:

Problem with a communication signal resulting from non-uniform connected components transmission speeds.

DISTRIBUTED ARCHITECTURE:

A term used to identify a Local Area Network (LAN) that uses a shared communications medium.

DISTRIBUTED CEF:

One of two modes of CEF (Cisco Express Forwarding) operation that enables line cards to perform the express forwarding between port adapters.

DISTRIBUTED COMMUNICATIONS ARCHITECTURE (DCA):

Data network architecture used in Sperry Univac ( UNISYS ) computer networks.

DISTRIBUTED OFFICE SUPPORT SYSTEM (DISOSS):

Refers to IBM Office System Node software

DISTRIBUTED PROCESSING / DISTRIBUTED DATA PROCESSING:

Generally, the ability of network nodes (sites) to execute shared network applications (processing), or parts of network applications, independently of other nodes.

DISTRIBUTED SYSTEMS ARCHITECTURE (DSA):

The data network architecture of Honeywell Corporation.

DISTRIBUTED SYSTEMS NETWORKING (DSN):

The data network architecture of Hewlett-Packard Corporation.

DISTRIBUTION FRAME (Main Frame):

A structure for terminating wires (lines/devices) of a telephone central office, PBX, private exchange or other communications media, which allows for easy change of connections via strapping and cross connecting wires.

DISTRIBUTION POINT:

X.500 Directory entry or other information source that is named in a v3 X.509 public-key certificate extension; a location from which to obtain a CRL that might list the certificate

DIT:

Directory Information Tree: Global tree of entries corresponding to information objects in the OSI X.500 Directory.

DIVERSITY:

Diversity of Transmission - Telecommunications reliability may be improved through various forms of ‘diversity’ (functional variations) throughout the system. These may include time constraints, space, frequency, route, path or other forms of routing and functions. Different degrees of availability (or reliability) may be achieved depending upon the nature of the diversity used.

DIVESTITURE:

The breakup of AT&T by the federal court based on an antitrust agreement reached between AT&T and the U.S. Department of Justice, effective January 1, 1984.

DLA:

Defense Logistic Agency

DLC:

See Data Link Control

DLCI:

Data-Link Connection Identifier: A value that specifies a Permanent Virtual Circuit (PVC) or a Switched Virtual Circuit (SVC) in a Frame Relay network. In the basic Frame Relay specification, DLCI(s) are locally significant because connected devices might use different values to specify the same connection. In the LMI extended specification, DLCI(s) are globally significant and they specify individual end devices.

DLE:

Data Link Escape: A control character which changes the meaning of a limited number of contiguously following characters.

DLL:

Dynamic Link Library

DLSw:

Data-Link Switching: Interoperability standard, described in RFC 1434, that provides a method for forwarding SNA and NetBIOS traffic over TCP/IP networks using data-link layer switching and encapsulation. DLSw uses SSP instead of SRB, eliminating the major limitations of SRB, including hop-count limits, broadcast and unnecessary traffic, timeouts, lack of flow control, and lack of prioritization schemes.

DLSw+:

Data-Link Switching Plus: Cisco implemented DLSw standard for SNA and NetBIOS traffic forwarding. DLSw+ goes beyond the previous standard to include the advanced features of the current Cisco RSRB implementation, and provides additional functionality to increase the overall scalability of data-link switching.

DLUR:

Dependent LU Requester: Client half of the Dependent LU Requestor / Server enhancement to APPN. The DLUR component resides in APPN EN(s) and NN(s) that support adjacent DLU(s) by securing services from the DLUS.

DLUR NODE:

In APPN networks: An EN or a NN that implements the DLUR component.

DLUS:

Dependent LU Server: Server half of the Dependent LU Requestor / Server enhancement to APPN. The DLUS component provides SSCP services to DLUR nodes over an APPN network.

DLUS NODE:

In APPN networks, an NN that implements the DLUS component

DM:

1) Data Memory: Storage media for transferring blocks of data to/from a processor.

2) Delta Modulation: A variant of pulse code modulation; a coded representation of the difference between the amplitude of a sample pulse and of the previous pulse. DM Operates satisfactorily in the presence of noise but requires a wide frequency band.

3) Discard Message: A control character used to reject or delete a message.

DMA:

Direct Memory Access: Direct access to computer memory from peripheral controllers without going through the arithmetic processing unit.

DMAC:

Destination MAC: The MAC address specified in the Destination Address field of a packet.

DMC:

Defense Mega-center Columbus: Consolidated Defense Agency (DLA) data message relay center located in Columbus, OH.

DMDP:

DNSIX Message Deliver Protocol: DMDP provides a basic message-delivery mechanism for all DNSIX elements.

DMI:

Digital Multiplexed Interface: An AT&T Local Area Network (LAN) voice/ data Private Automatic Branch Exchange (PABX) standard designed for using T1 transmission, with 64kbps channels.

DML:

Data Manipulation Language

DMM:

1. Dual MICA Module: Contains 12 discrete MODEM(s)

2. Duo-Decimal MODEM Module: MICA technologies hardware packaging with 12 MODEM(s) on a daughter card unit.

DMP:

1) Device Management Protocol: The session-layer communications protocol used within the ICM. Different application-level protocols might be running beneath DMP.

2) Data Movement Processor: Processor on the Catalyst 5000 that, along with the multi-port packet buffer memory interface, performs the frame-switching function for the switch. The DMP also handles translational bridging between the Ethernet and FDDI interfaces, IP segmentation, and intelligent bridging with protocol-based filtering.

DMS:

1) Digital Multiplex System: Switching systems that provide digital circuit-switched service for voice and data transmission and packet switched service for data transmission. DMS is characterized by the use of pulse code modulation (PCM) and time division multiplexing (TDM) throughout the switched network. The system allows the direct switching of PCM signals, without conversion to an analog format.

2) Defense Message System: A program designed to facilitate and coordinate the development of an integrated common-user message system for the Department of Defense (DoD). It provides end-to-end global electronic messaging service within DoD. Basically DMS is a secure Internet media, which provides worldwide connections for data communications. The DMS replaces the centralized AUTODIN message system, the DDN E-mail components, and the formats and procedures of the current message distribution baseline.

DMS - SERVICE CONTROL CENTER:

A hierarchical structure of centers that manages the DMS infrastructure

DMT:

Discrete Multi-Tone: A process that uses digital signal processors to transmit more than 6 Mbps of data, video, image and voice signals on a pair of copper wiring.

DN:

1) Dialed Number: Number that a caller dialed to initiate a call; for example, 800-666-1313

2) Distinguished Name: Global, authoritative name of an entry in the OSI Directory (X.500).

DNA:
1) Digital Network Architecture: A Digital Equipment Corporation proprietary digital network architecture. The products that embody DNA (including communications protocols) are referred to collectively as DECnet.

2) Do-Not-Age: Most significant bit of the LS Age (LSA) field. LSA(s) having the Do-Not-Age bit set are not aged as they are in the link-state database of the OSPF (Open Shortest Path First) router, which means that these LSA(s) need not be refreshed every 30 minutes.

DNIC:

Data Network Identification Code: A 4-digit Public Data Network (PDN) identification code used in a packet-switching network.

DNIS:

Dialed Number Identification Service (called number): A feature on trunk lines where the called number is identified and the called number information is used to route the call to the appropriate service. DNIS is a service used with toll-free dedicated services where calls placed to specific toll-free numbers are routed to the appropriate area within a company.

DNS:

Domain Name System: A naming or identification system for host computer (server) systems on the Internet. The host computer on the Internet will have a domain name, ‘autodin.net’ and an associated numerical IP address of 4 octets separated by periods, 199.6.33.22. DNS is also an acronym for ‘Domain Name Service’, the Internet utility that implements the Domain Name System.

DNS ZONE:

Domain Name Server Zone: Point of delegation in the DNS tree. It contains all names from a certain point downward except those for which other zones are authoritative. Authoritative name servers can be asked by other DNS(s) for name-to-address translation. Many name servers can exist within an organization, but only those known by the root name servers can be queried by the clients across the Internet. Other name servers answer only internal queries.

DNSIX:

Department of Defense Intelligence Information System Network - Security for Information Exchange: Collection of security requirements for networking defined by the U.S. Defense Intelligence Agency.

DOC FILE:

A Microsoft Word Document File: In the past, these files contained only document data, but with many newer versions of Microsoft Word, DOC files also include small programs called macros. Many virus authors use the macro programming language to associate macros with DOC files. This file type has the extension DOC.

DOCK:

To connect a laptop or notebook computer to a docking station. See Docking Station

DOCKING STATION:

A unit for housing a portable computer that contains a power connection, expansion slots, and connections to peripherals, such as a monitor, printer, full-sized keyboard, and mouse. The docking station turns the portable computer into a desktop computer.

DOCSIS:

Data-over-Cable Service Interface Specifications: Defines technical specifications for equipment at both subscriber locations and cable operator head-ends. Adoption of DOCSIS will accelerate the deployment of data-over-cable services and will ensure interoperability of equipment throughout system operation infrastructures.

DOCSIS CM:

DOCSIS Cable MODEM

DOCSIS CMTS:

DOCSIS Cable MODEM Termination System

DOCSIS CONFIGURATION FILE:

A file containing configuration parameters for a DOCSIS cable MODEM: The cable MODEM obtains this file at boot time using the TFTP protocol.

DoD, DOD:

Department of Defense

DOD:

See Direct Outward Dialing

DOI:

Domain of Interpretation: In Internet Protocol Security (IPSec), an ISAKMP/IKE DOI defines payload formats, exchange types, and conventions for naming security-relevant information such as security policies or cryptographic algorithms and modes.

DOMAIN:

1) The Internet, for example, is divided into smaller sets known as domains, such as: .com (business), .gov (government), .edu (educational), etc.

2) In SNA (Systems Network Architecture): an SSCP (System Services Control Points) and the resources it controls.

3) In IS-IS (Intermediate System-to-Intermediate System): a logical set of networks.

4) In security: an environment or context that is defined by a security policy, a security model, or a security architecture; a set of system entities that have the right to access the resources.

DOMAIN LOCAL GROUP:

A security or distribution group that can contain universal groups, global groups, and accounts from any domain in the domain tree: A domain local group can also contain other domain local groups from its own domain. Rights and permissions can be assigned only at the domain containing the group.

DOMAIN NAME:

The name of an Internet site, which allows direct references to Internet sites without knowing the true numerical address.

DOMAIN NAMESPACE:

The database structure used by the Domain Name System (DNS): See DNS

DOMAIN NAME SYSTEM:

See DNS

DOMAIN TREE:

   In DNS (Domain Name System), the inverted hierarchical tree structure that is used to index domain names. Domain trees are similar in purpose and concept to the directory trees used by computer filing systems for disk storage.

For example: when numerous files are stored on disk, directories can be used to organize the files into logical collections. When a domain tree has one or more branches, each branch can organize domain names used in the namespace into logical collections.

   In Active Directory: a hierarchical structure of one or more domains connected by transitive, bidirectional trusts that form a contiguous namespace. Multiple domain trees may belong to the same ‘forest’.

DoN:

Department of Navy

DOS:

Disk Operating System: A Disk management operating system which manages disk files (address and area) and schedules or supervise work, manage resources, and controls peripherals.

DOT ADDRESS:

Refers to the common notation for Internet Protocol (IP) addresses in the form n n n n, where each number n represents, in decimal, 1 byte of the 4-byte IP address; also called dotted notation or four-part dotted notation.

DOTTED DECIMAL NOTATION:

Syntactic representation for a 32-bit integer that consists of four 8-bit numbers written in base 10 with periods (dots) separating them; used to represent IP addresses on the Internet, example: 192.67.67.20. May also be called dotted quad notation

DOUBLE BYTE CHARACTERS:

A set of characters in which each character is represented by two bytes: Some languages, such as Japanese, Chinese, and Korean, require double-byte character sets.

DOUBLE PARITY:

Refers to a system using both vertical and horizontal parity schemes

DOWN LINK:

May refer to a satellite signal used to transmit information to an earth station, or may refer to a transmission link (connection/operation) between two devices.

DOWNLOAD / DOWNLOADING / DOWNLINE LOADING:

The process of copying data file(s) from a remote computer to a local computer. The opposite action is up-load where a local file is copied to a remote computer.

DOWNLOADABLE FONTS:

A set of characters stored on disk and sent (downloaded) to a printer's memory when needed for printing a document. Downloadable fonts are most commonly used with laser printers and other page printers, although many dot-matrix printers can accept some of them. Downloadable fonts are also called soft fonts.

DOWNSTREAM:

Refers to the host to end-user (receive - download) direction.

DOWNTIME:

Refers to the time period when all or part of a computer system, device or data network is not available for service. Preventive maintenance time may or may not be considered down time.

DOV:

See Data-Over-Voice

DPSK:

Differential Phase-Shift Keying: A modulation technique in which the relative changes of a carrier sine wave phase occur according to the data transmitted.

DPCM:

Differential Pulse Code Modulation: A method of digital encoding in which the analog signal is sampled and the difference between each sample of the signal and its prior estimated value is quantified and digitally encoded.

DPM:

Call Defect Per Million: Lost stable (connected call) or non-stable (call setup) call due to any hardware or software failure, procedural error, or other causes. Note: A Call Defect does not include misrouted calls or loss of call features.

DQDB:

Distributed Queue Dual Bus: Data-link layer communication protocol, specified in the IEEE 802.6 standard designed for use in MAN(s). DQDB permits multiple systems to interconnect using two unidirectional logical buses, and is an open standard that is designed for compatibility with carrier transmission standards, and is aligned with emerging standards for BISDN. SIP is based on DQDB.

DQM:

Data Quality Monitor: A bias (distortion) measuring device used to check the data bias status. May be used for preventative maintenance or because a data error(s) condition exists.

DRAIN MESSAGE:

A term used when accumulated messages in a store and forward message switching system are removed and at the same time incoming messages may be inhibited while the drain process is in effect.

DRAG:

To move an item on the screen by selecting the item and then pressing and holding down the mouse button while moving the mouse. For example: move a window to another location on the screen by dragging its title bar

DRAM:

See Dynamic Random Access Memory

DRDA:

Distributed Relational Database Architecture: IBM proprietary architecture

DRIVE:

An area of storage that is formatted with a file system and has a drive letter: The storage can be a floppy disk, a CD, a hard disk, or another type of disk. View the contents of a drive by clicking its icon in Windows Explorer or My Computer.

DRIVE LETTER:

The naming convention for disk drives on IBM and compatible computers. Drives are named by letter, beginning with A, followed by a colon.

DRIVER:

Line Driver, Controller - A software/hardware module used to control an input/output port.

DRY CIRCUIT:

A circuit which transmits voice signals and carries no direct current.

DROP AND INSERT:

Allows DSO channels from one T1 or E1 facility to be cross-connected digitally to DS0 channels on another T1 or E1: By using this method, channel traffic is sent between a PBX and a CO PSTN switch or other telephony device, so that some PBX channels are directed for long-distance service through the PSTN while the router compresses others for interoffice VoIP calls. In addition, Drop and Insert can cross-connect a telephony switch, from the CO or PSTN, to a channel bank for external analog connectivity. May also be called TDM Cross-Connect

DROP CABLE or DROP:

In a Local Area Network (LAN) environment, this would refer to the cable that connects a branch to the main, or bus cable and/or Data Terminal Equipment (DTE). In other uses could be a terminal connected to a network, multi-point line, or system, or the line from a telephone cable to a subscriber's building.

DRP:

Director Response Protocol: Protocol used by the Distributed Director feature in IP routing.

DROPPER:

A dropper is carrier file that installs a virus on a computer system. Virus authors often use droppers to shield their viruses from anti-virus software. The term injector often refers to a dropper that installs a virus only in memory.

DRUM:

A cylinder having a surface coating of magnetic material that stores binary information through magnetic dipoles (heads) near its surface. Since the drum rotates at a uniform rate, the information stored is available periodically as a given portion of the surface moves past one or more fixed flux detecting heads located near the surface of the drum. Addressing the surface is provided by electrically segmenting the drum surface into parts, tracks and sectors. Tracks circled the drum and the tracks were divided into parts (sectors).  Later disk devices used moving heads, which could move across the surface for writing and reading information.

DS:

Data Set or Digital Signals: Data Set - A device that converts data into signals (digital to analog) suitable for transmission over communications lines; the AT&T name for a MODEM. See Digital signals

DS0:

Digital Service Zero (0): Single timeslot on a DS1 (T1) digital interface; a 64-kbps, synchronous, full-duplex data channel, typically used for a single voice connection on a PBX.

DS-1:

Digital Service hierarchy level 1: Has a maximum channel capacity of 1.544Mbps. This term is used interchangeably with T1; 24 DS-0 channels per DS1.

DS-1C:

Digital Service level 1C: Designation for digital signals operating at a maximum channel capacity of 3.152 mbps.

DS-1/DTI:

DS-1 Domestic Trunk Interface: Interface circuit used for DS-1 applications with 24 trunks.

DS-1 FRAMING ERRORS:

Frame synchronization bit errors detected by the Model 6302 Dataphone Digital Service (DDS), DDS Test Unit (DTU), in either terminal framing (Ft) or signaling framing (Fs) bits.

DS-1 PERFORMANCE UNIT (DPU):

The Hekimian Model 6301 test set that provides in service monitoring and also provides out of service testing of DS-1 signals.

DS-1 SIGNAL ACCESS UNIT (DSAU):

A plug in circuit pack used in Dataphone Digital Service (DDS) hub offices. This unit provides full duplex access to a DS-1 signal, allowing centralized maintenance and testing.

DS-2:

Digital Service level 2: Refers to digital signals operating at a maximum channel capacity of 6.312 mbps on a T2 facility.

DS-3:

Digital Service hierarchy level 3: with a maximum channel capacity of 44.736. This term is used interchangeably with the T3, 28 DS-1 channel, per DS-3.

DS-3 TEST UNIT:

The Hekimian Model 6305 test set that provides complete monitoring and testing capabilities for DS-3 circuits.

DSA:

Directory Service Agent: Software that provides the X.500 (ITU-T recommendation) Directory Service for a portion of the directory information base. Generally, each DSA is responsible for directory information concerning a single organization or organizational unit.

DSA, Inc:

Data Systems Analyst, Inc.: A software development company.

DSAP:

Destination Service Access Point: SAP of the network node designated in the Destination field of a packet.

DSCS:

Defense Satellite Communications System: Consists of links on 10 military satellites to sites around the globe

DSE:

Digital Switching Exchange: A node in a telecommunications network

DSF:

Dispersion-Shifted Fiber; A type of single-mode fiber designed to have zero dispersion near 1550 nm.

DSL:

Digital Subscriber Line: A generic term describing a subscriber's (leased / owned) existing copper lines, and refers to the underlying technology inherent in all types of DSL such as ADSL, SDSL and HDSL. For instance a couple of ADSL (Asymmetric Digital Subscriber Line) Internet Service options will support information transfer rates of 1.5 Mbps downstream and 384 Kbps upstream, or 384 Kbps downstream and 128 Kbps upstream.

DSL GATEWAY:

Refers to DSL network equipment, remotely located, that enable residential and business customers to receive DSL Internet Service when they are located too far from their main central switching office. The Gateway is a miniature central office that allows the delivery of DSL Internet Service beyond the standard 14,000 to 15,000 foot limit of a traditional central switching office.

DSLAM:

Digital Subscriber Line Access Multiplexer: A device that concentrates a number of ADSL subscribers lines into a single ATM line.

DSL MODEM:

A Digital Subscriber Line hardware device that converts ATM cells to Ethernet packets and visa-versa.

DSn:

Digital Signal Level n: A classification of digital circuits. The DS technically refers
to the rate and the format of the signal, where the T designation refers to the equipment providing the signals. In practice, DS and T are used synonymously; example: DS1 and T1, DS3 and T3.

DSN:

1) Defense Switching Network: The DSN is the principal common user, switched, non-secure voice communications network within the DCS. It consists of a worldwide network of commercial leased and government-owned facilities. Tactical DSN subscribers normally gain access through the Theater Communications System (TCS) using the AN/TTC-39 circuit switch. The TCS provides circuit or message switches and direct access to many worldwide DOD networks.

2) Digital Switched Network: High-speed digital switched public network, which allows users to access a large range of various calling capabilities.

3) Delivery Status Notification: Message returned to the originator indicating the delivery status of an e-mail message. A sender can request three types of delivery status notifications: delay, success, and failure.

DSNET:

Defense Secure Network

DS0:

The AT&T Bell System level 0 digital standard for systems operating at 64-Kbps. Examples of other standards: 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 – is the AT&T Bell System level 3 digital standard for systems operating at 44.736 (45) Mbps.

DSP:

1) Digital Signal Processor: Basically a parallel microprocessor optimized for high efficiency processing of communications signals. For instance: A DSP segments the voice signal into frames and stores them in voice packets.

2) Domain Specific Part: Part of a Network Service Access Point (NSAP)-format ATM (Asynchronous Transfer Mode) address that contains an area identifier, a station identifier, and a selector byte.

DSPU:

Downstream Physical Unit: In SNA, a PU that is located downstream from the host.

DSPU CONCENTRATION:

Cisco IOS feature that enables a router to function as a PU concentrator for SNA PU 2 nodes. PU concentration at the router simplifies the task of PU definition at the upstream host, while providing additional flexibility and mobility for downstream PU devices.

DSPWARE:

Firmware running on the DSP co-processor

DSR:

Data Set Ready: A RS232 (x) signal that indicates that the MODEM is on, and ready to accept input from the computer or other source.

DSSCS:

Defense Special Security Communications System: An Intelligence Community (NSA, DIA, CIA) worldwide messaging system.

DSTC:

DSU Transfer Channel Control Unit: A part of a transfer Channel that controls timing and functions to allow transfer of data between the computer and a device (drum, disk).

DSTE:

Digital Subscriber Terminal Equipment / Data Station Terminal Equipment: Outstation, Terminal, and/or remote send/receive equipment.

DSU:

1) Drum (or Disk) Storage Unit. See drum or disk.

2) See Data Service Unit.

DSX:

Digital System Cross-Connect: An internal interface (structural) that functions as a central point for cross-connecting, rearranging, patching, and testing digital equipment and facilities.

DSX-1:

Digital Signal Cross-Connect Level 1: A set of parameters used when (DS-1) Digital Signals are cross connected.

DT:

1) Data Terminal: A station (terminal) in a system capable of sending and/or receiving data (messages).

2) Drum Transfer Channel (port): The data transfer media between the Drum and the computer.

DTAS:

Digital Test Access System: Hekimian's family of digital access and test equipment

DTAU:

Digital Test Access Unit: A subset of the digital access and test equipment included in Hekimian's DTAS product line. This equipment provides split and hitless monitor access to T1 lines for maintenance and testing.

DTD:

Document Type Definition or Document Type Declaration: used in SGML and XML markup languages to specify the set of rules for a particular language. HTML versions each have their own DTD.

DTE:

Data Terminal (or Termination) Equipment

1) The equipment that converts user information into data signals for transmission, or vice versa. This equipment could include control logic, buffer, input or output devices or computers. It could also provide error control, synchronization, and station identification capability.

2) RS-449 DTE Ready signal (Pin 12A & 30B) – indicates the DTE is operational.

DTF:

Data Transfer Facility: A device that provides bi-directional data transfer between an IBM MVS system in a System Network Architecture (SNA) environment and VAX/VMS systems in a DECnet network.

DTH:

Defense Message System Transition Hub: AUTODIN replacement system. Refer to DMS.

DTI:

Data Terminal Interface: The connection and/or control point between a data terminal and telephone system.

DTL:

Designated Transit List: List of nodes and optional link identifications (ID) that completely specify a path across a single PNNI peer group

DTMF:

Dual Tone Multi-Frequency: A term used to describe the audio signaling frequencies where each key generates two audio tones. Contrast with pulse dialing.

DTMF RELAY:

Dual Tone Multi-Frequency Relay: Mechanism where a local Voice over IP (VoIP) gateway listens for DTMF digits during a call, and then sends them uncompressed as either RTP or H.245 packets to the remote Voice over IP gateway, which regenerates DTMF digits and prevents digit loss due to compression.

DTP:

DDSN Transfer Protocol: Process on the ICM Logger that connects to Cisco Customer Support and delivers any messages saved by the Customer Support Forwarding Service (CSFS). The DTP is part of the Distributed Diagnostics and Service Network (DDSN), which ensures that Cisco Customer Support is informed promptly of any unexpected behavior within the ICM.

DTR:

Data Terminal Ready: A RS232 (X) signal sent from the computer to the MODEM indicating the computer is ready to communicate.

DTS:

Digital Termination System: A Federal Communications Commission (FCC) system that regulates cellular radio local access and microwave/satellite long distance.

DTU:

See DDS Test unit

DUA:

Directory User Agent: Software that accesses the X.500 Directory Service on behalf of the directory user. The directory user can be a person or another software element.

DUAL:

Diffusing Update Algorithm: Convergence algorithm used in Enhanced IGRP that provides loop-free operation at every instant throughout a route computation. Allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change.

DUAL BAND:

A feature that allows some wireless phone handsets to operate using either the 800 MHz cellular or the 1900 MHz PCS (Personal Communication Services) frequencies

DUAL BOOT:

A computer configuration that can start two different operating systems

DUAL COUNTER-ROTATING RINGS:

Network topology in which two signal paths, whose directions are the opposite of each other, exist in a token-passing network; FDDI and CDDI are based on this concept.

DUAL HOMING:

Network topology in which a device is connected to the network by way of two independent access points (points of attachment). One access point is the primary connection, and the other is a standby connection that is activated in the event of a failure of the primary connection.

DUAL HOMED STATION:

Device attached to multiple FDDI rings to provide redundancy.

DUAL IN LINE PINS or DUAL IN LINE PACKAGE:

See DIP

DUAL MODE:

A feature on some wireless phones that allows the handset to operate on both analog and digital networks

DUAL TONE MULTI-FREQUENCY:

See DTMF

DUBLIN CORE:

A proposed set of standard descriptive metadata elements used with web resources to aid in resource discovery. The elements are intended as a starting point for resource description. The elements are optional, and are intended to be extensible to richer descriptive elements when needed. The 15 elements are: title, author/creator, subject/keywords, description, publisher, other contributor, date, resource type, format, resource identifier, source, language, relation, coverage and rights management.

DUMB TERMINAL:

Usually refers to a simple terminal, such as a Teletype or Cathode Ray Tube (CRT) terminal that may not perform error detection or use communications protocols, and is usually asynchronous operation.

DUPLEX:

Full Duplex/Duplex Transmission: Refers to any communications facility/device that provides for simultaneous data transmission in both directions.

DUPLEX CIRCUIT OR CHANNEL:

Simultaneous two-way (send and receive) data transmission and independent transmission (full Duplex)

DUPLEXING (Redundancy/Tandem):

Usually refers to the availability of duplicate processors, devices, files or circuitry, which would allow the system to continue functioning under abnormal conditions.

DUV:

Data under Voice: Refers to the normally unused lower end spectrum of a radio channel that is used to provide a T1 (1.544 mbps) channel for digital services.

DVB:

Digital Video Broadcasting: Consortium of around 300 companies in the fields of broadcasting, manufacturing, network operation, and regulatory matters working to establish common international standards for the move from analog to digital broadcasting.

DVB-C:

DVB digital cable delivery system: Digital cable system that is compatible with DVB-S.

DVMRP:

Distance Vector Multicast Routing Protocol: Inter-network gateway protocol, largely based on RIP, that implements a typical dense mode IP multicast scheme.

DVVI:

Data, Voice, Video Integration

DWDM:

Dense Wavelength Division Multiplexing: Optical transmission of multiple signals over closely spaced wavelengths in the 1550 nm region. Wavelength spacing is usually 100 GHz or 200 GHz, which corresponds to 0.8 nm or 1.6 nm.

DXI:

Data Exchange Interface: An SMDS interface between the customer and the network, normally low speed, typically 64 kbps. The data passes through the interface in full frames. The carrier's equipment then converts the messages to small packets.

DYNAMIC ADAPTIVE ROUTING:

Automatic rerouting of traffic based on a sensing and analysis of current actual network conditions, not including cases of routing decisions taken on predefined information.

DYNAMIC ADDRESS RESOLUTION:

Use of an address resolution protocol to determine and store address information on demand

DYNAMIC BUFFER MANGEMENT:

Frame Relay and ATM service modules are equipped with large buffers and the patented Dynamic Buffer Management is a scheme for allocating and scaling traffic entering or leaving a node on a per-VC basis. The WAN switch dynamically assigns buffers to individual virtual circuits based upon the amount of traffic present and service-level agreements. This deep pool of available buffers readily accommodates large bursts of traffic into the node.

DYNAMIC CONFIGURATION:

‘Discovery Mode’: Method by which an AppleTalk interface acquires information about an attached network from an operational node; then uses this information to configure itself

DYNAMIC DISK:

A physical disk that can be accessed only by Windows 2000 and Windows XP: Dynamic disks provide features that basic disks do not, such as support for volumes that span multiple disks. Dynamic disks use a hidden database to track information about dynamic volumes on the disk and other dynamic disks in the computer. Convert basic disks to dynamic by using the Disk Management snap-in or the Disk-Part command line utility. When a basic disk is converted to a dynamic disk all existing basic volumes become dynamic volumes.

DYNAMIC HOST CONFIGURATION PROTOCOL (DHCP):

A TCP/IP (Transmission Control Protocol/Internet Protocol) service protocol: That offers dynamic leased configuration of host IP (Internet Protocol) addresses and distributes other configuration parameters to eligible network clients. DHCP provides for safe, reliable, and simple TCP/IP network configuration, and prevents address conflicts, and helps conserve the use of client IP addresses on the network.

DHCP uses a client/server model where the DHCP server maintains centralized management of IP addresses that are used on the network. DHCP-supporting clients can then request and obtain lease of an IP address from a DHCP server as part of their network boot process.

DYNAMIC HTML (DHTML):

A HTML expansion that allows absolute control over element positioning on a page and also greater control of events; it is supported by MSIE 4.0 and partially by Netscape 4.0.

DYNAMIC IISP:

Dynamic Interim-Inter-switch Signaling Protocol: Basic call routing protocol that automatically reroutes ATM connections in the event of link failures.

DYNAMIC IP ADDRESSING:

An Internet Protocol (IP) address that is temporarily assigned to the customer for and during their current on-line session by the Internet Service Provider (ISP)

DYNAMIC LINK LIBRARY (DLL):

An operating system feature: That allows executable routines, generally serving a specific function or set of functions, to be stored separately as files with .dll extensions. These routines are loaded only when needed by the specific program.

DYNAMIC MULTIPLEXING:

Refers to a form of time division multiplexing in which allocation of time is made according to the demands of the connected channels.

DYNAMIC NODE ADDRESS:

An Apple Computer feature of AppleTalk where each time a node is initialized it assigns itself a unique address code. Normally nodes are assigned fixed addresses that do not change.

DYNAMIC RANDOM ACCESS MEMORY (DRAM):

Random Access Memory (RAM) that requires electronic refresh cycles every few milliseconds to preserve its data.

DYNAMIC ROUTING:

A process where a system will automatically re-route messages across a network if a line fails or the line or system is overloaded. Packet switching operates on this principle, with the system ready to react to ever changing conditions. In static routing the data is sent along pre-programmed (pre-assigned) paths and is delayed if that path becomes blocked.

DYNAMIC SCHEDULING:

In computerized communications systems decisions concerning program execution are made by the computer from moment to moment, depending on events taking place. The processing schedule in a communications system changes dynamically with service, demand rates, and event sequences.

DYNAMIC STORAGE:

A storage method in Windows: That allows disk and volume management without requiring operating system restart.

DYNAMIC SWITCHED CALL:

Telephone call dynamically established across a packet data network based on a dialed telephone number. In the case of Voice over Frame Relay (VoFR), a Cisco proprietary session protocol similar to Q.931, is used to achieve call switching and negotiation between calling endpoints. The proprietary session protocol runs over FRF.11-compliant sub-channels.

DYNAMIC SYSTEMS DIAGNOSIS:

Refers to Communications and/or Private Branch Exchange (PBX) systems that allow system diagnostic (maintenance) programs to be selected and run concurrently with normal system operation.

DYNAMIC VOLUME:

A volume that resides on a dynamic disk: Windows supports five types of dynamic volumes: simple, spanned, striped, mirrored, and RAID-5. A dynamic volume is formatted by using a file system, such as FAT (File Allocation Table) or NTFS, and it has a drive letter assigned to it.

DYNAMICALLY CONTROLLED ROUTING (DCR):

A function of changing transmission routing patterns based on network load.