D

 

D Channel:  the Integrated Services Digital Network (ISDN), the D-channel is the channel that carries control and signalling information. (The "D" stands for "delta" channel.) The B-channel ("B" for "bearer") carries the main data. In ISDN, there are two levels of service: the Basic Rate Interface, intended for the home and small enterprise, and the Primary Rate Interface, for larger users. Both rates include a number of B- (bearer) channels and a D- (delta) channel. The B-channels carry data, voice, and other services. The D-channel carries control and signaling information. The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate Interface user can have up to 128 Kbps service. The Primary Rate Interface consists of 23 B-channels and one 64- Kpbs D channel in the United States or 30 B-channels and 1 D-channel in Europe.  [WhatIs.com]

DAC (Data Acquisition and Control): which is a front end to a SCADA system dedicated to managing the communication protocols from RTUs and IEDs. The DAC also handles the monitoring of the remote data and passes  the control commands from the SCADA to the end devices. [Common Usage]

DAF (Data Access Facility): DAF is an API developed for the OMG group to access model data needed for simulation and analysis applications from a utility SCADA, EMS, or DMS system on a read-only basis. [OMG]

DAIS (Data Acquisition from Industrial Systems): DAIS is an API developed for the OMG group to support efficient real time transfer of large amounts of data from an real-time process to a wide range of clients, to permit the discovery of parameters, and to allow the update of parameter values. [OMG]

DAIS™: Data Access Integration Services

DAMA (Demand Assigned Multiple Access): In a communications system, a technique for allocating use of bandwidth among multiple users, based on demand. Note: DAMA can be implemented in many ways including TDM and FDM.   In particular, some of the more sophisticated satellite systems and digital cellular phone systems use DAMA. [T1 Glossary 2000: Glossary of Telecommunications Terms]

DARPA (U.S. Defense Advanced Research Project Agency): DARPA is the central research and development organization for the Department of Defense (DoD). It manages and directs selected basic and applied research and development projects for DoD. DARPA developed a computer network called ARPAnet. [http://www.arpa.mil].

Data Attribute:  defines the name (semantic), format, range of possible values, and representation of values while being communicated. [IEC61850-2]

Data Circuit-terminating Equipment (DCE):  Abbreviation for data circuit-terminating equipment. 1. In a data station, the equipment that (a) performs functions, such as signal conversion and coding, at the network end of the line between the data terminal equipment (DTE) and the line, and (b) may be a separate or an integral part of the DTE or of intermediate equipment. 2. The interfacing equipment that may be required to couple the data terminal equipment (DTE) into a transmission circuit or channel and from a transmission circuit or channel into the DTE. Synonyms data communications equipment (deprecated) , data set (deprecated). 3. Abbreviation for distributed computing environment. An architecture of standard programming interfaces, conventions, and server functionalities (e.g., naming, distributed file system, remote procedure call) for distributing applications transparently across networks of heterogeneous computers. [T1 Glossary 2000: Glossary of Telecommunications Terms] 

Data Confidentiality: See Confidentiality

Data Encryption Standard (DES): [A] cryptographic algorithm for the protection of unclassified computer data and published by the National Institute of Standards and Technology (NIST) in Federal Information Processing Standard (FIPS) Publication 46-1. [INFOSEC-99] Note: DES is not approved for protection of national security classified information.  [T1 Glossary 2000: Glossary of Telecommunications Terms]  DES is a widely-used method of data encryption using a private (secret) key that was judged so difficult to break by the U.S. government that it was restricted for exportation to other countries. There are 72,000,000,000,000,000 (72 quadrillion) or more possible encryption keys that can be used. For each given message, the key is chosen at random from among this enormous number of keys. Like other private key cryptographic methods, both the sender and the receiver must know and use the same private key. DES applies a 56-bit key to each 64-bit block of data. The process can run in several modes and involves 16 rounds or operations. Although this is considered "strong" encryption, many companies use "triple DES", which applies three keys in succession. This is not to say that a DES-encrypted message cannot be "broken." Early in 1997, Rivest-Shamir-Adleman (RSA), owners of another encryption approach, offered a $10,000 reward for breaking a DES message. A cooperative effort on the Internet of over 14,000 computer users trying out various keys finally deciphered the message, discovering the key after running through only 18 quadrillion of the 72 quadrillion possible keys! Few messages sent today with DES encryption are likely to be subject to this kind of code-breaking effort.   [WhatIs.com]  Alternatives to basic DES are 3DES (DES applied three times) and AES.

Data Integrity: 1. [The] condition existing when data is unchanged from its source and has not been accidentally or maliciously modified, altered, or destroyed. [INFOSEC-99] 2. The condition in which data are identically maintained during any operation, such as transfer, storage, and retrieval. 3. The preservation of data for their intended use. 4. Relative to specified operations, the a priori expectation of data quality. [T1 Glossary 2000: Glossary of Telecommunications Terms] 

Data link: 1. The means of connecting one location to another for the purpose of transmitting and receiving data. [JP 1-02] 2. An assembly, consisting of parts of two data terminal equipments (DTEs) and the interconnecting data circuit, that is controlled by a link protocol enabling data to be transferred from a data source to a data sink. [T1 Glossary 2000: Glossary of Telecommunications Terms] 

Data Link Layer: Layer 2. This layer responds to service requests from the Network Layer and issues service requests to the Physical Layer. The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer. Note: Examples of data link protocols are HDLC and ADCCP for point-to-point or packet-switched networks and LLC for local area networks. See OSI Reference Model.    [T1 Glossary 2000: Glossary of Telecommunications Terms]

Data Modeling: Data modeling is the analysis of data objects that are used in a business or other context and the identification of the relationships among these data objects. Data modeling is a first step in doing object-oriented programming. As a result of data modeling, you can then define the classes that provide the templates for program objects. A simple approach to creating a data model that allows you to visualize the model is to draw a square (or any other symbol) to represent each individual data item that you know about (for example, a product or a product price) and then to express relationships between each of these data items with words such as "is part of" or "is used by" or "uses" and so forth. From such a total description, you can create a set of classes and subclasses that define all the general relationships. These then become the templates for objects that, when executed as a program, handle the variables of new transactions and other activities in a way that effectively represents the real world. Several differing approaches or methodologies to data modeling and its notation have recently been combined into the Unified Modeling Language (UML), which is the de facto standard modeling language used by most industries.  [WhatIs.com] 

Data Object: part of a logical node object representing specific information e.g. status or measurement. From an object-oriented point of view a data object is an
instance of a data class. [IEC61850-2]  A Data Object is an abstract element of a real device that is capable of providing (when read) or accepting (when written) or both, a typed data value. A Data Object may represent a single data element (i.e., one measurement point) or a data structure (i.e., a complex set of data elements). The mapping of a Data Object to a real, physical entity in the device is defined by the model of the device being represented, and is outside the scope of this document. Data Objects are usually combined into functional Bricks, which are then used to construct a Device. Each Data Object has an associated Class, which defines its syntax. If the referenced Class contains common components, then the generic semantics from the common component is used by the Data Object to define specific semantics (e.g. the quality code common component will be used to define the quality of the value of the Data Object).  [Common Usage]

Data Type: A Data Type is a basic computer format (syntax) for data, e.g. Integer (INT16), Floating point (FLT64), Boolean (BOOL), Bitstrings (BSTRn), Visible Strings which are readable characters (VSTR32), etc.  [Common Usage]

Database: A computer holding large amounts of information that can be searched by an Internet user.  [Common Usage]

Datagram: In packet switching, a self-contained packet, independent of other packets, that contains information sufficient for routing from the originating data terminal equipment (DTE) to the destination DTE without relying on prior exchanges between the equipment and the network. Note: Unlike virtual call service, when datagrams are sent there are no call establishment or clearing procedures. Thus, the network may not be able to provide protection against loss, duplication, or misdelivery.  [T1 Glossary 2000: Glossary of Telecommunications Terms]   A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network. Defined in the OSI Reference Model as the data unit for the Transport layer. See also packet.  [WhatIs.com] 

DataSet: A DataSet is a ordered list of references to Data Objects associated with a specific DataSet Name, and is a means of grouping data together that is frequently accessed as a group. DataSets are used in ICCP and IEC 61850 to minimize the overhead for determining what data should be sent periodically. In IEC 61850, DataSets are used by the Report Control Blocks to determine what data to report periodically or upon exception. For instance, a DataSet could be defined as all status points in a particular Logical Unit; this DataSet would be associated with a Report Control Block which would report any status changes by exception, whenever they occur. [IEC61850]

Day-Ahead Market: The forward market for energy and ancillary services to be supplied during the settlement period of a particular trading day that is conducted by the Independent System Operator, the power exchange, and other Scheduling Coordinators. This market closes with the Independent System Operator's acceptance of the final day-ahead schedule.   [DOE Glossary of Electricity Terms]

Day-Ahead Schedule: A schedule prepared by a Scheduling Coordinator or the Independent System Operator before the beginning of a trading day. This schedule indicates the levels of generation and demand scheduled for each settlement period that trading day.   [DOE Glossary of Electricity Terms]

DB-9: DB-xx is the designation for a series of port connectors for attaching devices to computers. DB-xx connectors include DB-9, DB-15, DB-25, DB-50, and DB-68. DB-9 is a connector used for RS-232 connections and for several video interfaces on IBM-compatible computers. [WhatIs.com] 

DB-15: DB-xx is the designation for a series of port connectors for attaching devices to computers. DB-xx connectors include DB-9, DB-15, DB-25, DB-50, and DB-68.
DB-15 is a female connector used as a joystick port on IBM-compatible computers and as the video connector on Macintosh computers. There is also a high-density DB-15 female connector for the Video Graphics Array (VGA) or Super Video Graphics Array (SVGA) video adapter on IBM-compatible computers. [WhatIs.com] 

DB-25: DB-25 is a male connector used for attaching external modems and RS-232 serial peripherals on older IBM-compatible computers. The DB-25 female connector is the parallel port connector for most personal computers, typically used for parallel interface printers. DB-25 was first used with the original IBM personal computer (PC) and has had a long life. [WhatIs.com] 

DB-50: DB-50 is a female connector used as the SCSI-2 connector for 8-bit Narrow SCSI devices on older Sun and Data General computers. However, DB-50 is not recognized by the SCSI specifications.  [WhatIs.com] 

DB-68: DB-68 is a high-density connector used as a SCSI-3 connector for 16-bit Wide SCSI and Fast SCSI devices.  [WhatIs.com] 

DBMS: A database management system (DBMS), sometimes just called a database manager, is a program that lets one or more computer users create and access data in a database. The DBMS manages user requests (and requests from other programs) so that users and other programs are free from having to understand where the data is physically located on storage media and, in a multi-user system, who else may also be accessing the data. In handling user requests, the DBMS ensures the integrity of the data (that is, making sure it continues to be accessible and is consistently organized as intended) and security (making sure only those with access privileges can access the data). The most typical DBMS is a relational database management system (RDBMS). A standard user and program interface is the Structured Query Language (SQL). A newer kind of DBMS is the object-oriented database management system (ODBMS). [WhatIs.com] 

DCE: See Data Circuit-terminating Equipment

DCE: See Distributed Computing Environment

DCOM (Distributed Component Object Model): is a Microsoft developed protocol that enables software components to communicate directly over a network in a reliable, secure, and efficient manner. Previously called "Network OLE," DCOM is designed for use across multiple network transports, including Internet protocols such as HTTP. DCOM is based on the Open Software Foundation's DCE-RPC spec and will work with both Java applets and ActiveX® components through its use of the COM. [Microsoft]

DCS (Distributed Control System): DCS's are used in power plants and other energy production facilities as the primary control system and data highway.  [Common Usage]

DDN (Defense Data Network): A portion of the Internet, which connects to U.S. Military Bases and contractors; used for non-secure communications. MILNET is one of the DDN networks. It also runs "the NIC," where a lot of Internet information is archived.

Deadband: A deadband is the amount by which an analog input must change from the last reported value to be spontaneously reported.  [Common Usage]

Demand: The rate at which energy is delivered to loads and scheduling points by generation, transmission, and distribution facilities.   [DOE Glossary of Electricity Terms]

Demand (Electric): The rate at which electric energy is delivered to or by a system, part of a system, or piece of equipment, at a given instant or averaged over any designated period of time.    [DOE Glossary of Electricity Terms]

Demand Bid: A bid into the power exchange indicating a quantity of energy or an ancillary service that an eligible customer is willing to purchase and, if relevant, the maximum price that the customer is willing to pay.   [DOE Glossary of Electricity Terms]

Demand-Side Management: The planning, implementation, and monitoring of utility activities designed to encourage consumers to modify patterns of electricity usage, including the timing and level of electricity demand. It refers only to energy and load-shape modifying activities that are undertaken in response to utility-administered programs. It does not refer to energy and load-shape changes arising from the normal operation of the marketplace or from government-mandated energy-efficiency standards. Demand-Side Management (DSM) covers the complete range of load-shape objectives, including strategic conservation and load management, as well as strategic load growth.   [DOE Glossary of Electricity Terms]

Denial of Service Attack: 1. The prevention of authorized access to resources or the delaying of time-critical operations. [2382-pt.8] 2. The result of any action or series of actions that prevents any part of an information system (IS) from functioning. [INFOSEC-99] [T1 Glossary 2000: Glossary of Telecommunications Terms]  the Internet, a denial of service (DoS) attack is an incident in which a user or organization is deprived of the services of a resource they would normally expect to have. Typically, the loss of service is the inability of a particular network service, such as e-mail, to be available or the temporary loss of all network connectivity and services. In the worst cases, for example, a Web site accessed by millions of people can occasionally be forced to temporarily cease operation. A denial of service attack can also destroy programming and files in a computer system. Although usually intentional and malicious, a denial of service attack can sometimes happen accidentally. A denial of service attack is a type of security breach to a computer system that does not usually result in the theft of information or other security loss. However, these attacks can cost the target person or company a great deal of time and money. Common forms of denial of service attacks are:

• Buffer Overflow Attacks: The most common kind of DoS attack is simply to send more traffic to a network address than the programmers who planned its data buffers anticipated someone might send. The attacker may be aware that the target system has a weakness that can be exploited or the attacker may simply try the attack in case it might work. A few of the better-known attacks based on the buffer characteristics of a program or system include:
  Sending e-mail messages that have attachments with 256-character file names to Netscape and Microsoft mail programs
  Sending oversized Internet Control Message Protocol (ICMP) packets (this is also known as the Packet Internet or Inter-Network Groper (ping) of death)
  Sending to a user of the Pine e-mail program a message with a "From" address larger than 256 characters

• SYN Attack: When a session is initiated between the Transport Control Program (TCP) client and server in a network, a very small buffer space exists to handle the usually rapid "hand-shaking" exchange of messages that sets up the session. The session-establishing packets include a SYN field that identifies the sequence in the message exchange. An attacker can send a number of connection requests very rapidly and then fail to respond to the reply. This leaves the first packet in the buffer so that other, legitimate connection requests can't be accommodated. Although the packet in the buffer is dropped after a certain period of time without a reply, the effect of many of these bogus connection requests is to make it difficult for legitimate requests for a session to get established. In general, this problem depends on the operating system providing correct settings or allowing the network administrator to tune the size of the buffer and the timeout period.

• Teardrop Attack: This type of denial of service attack exploits the way that the Internet Protocol (IP) requires a packet that is too large for the next router to handle be divided into fragments. The fragment packet identifies an offset to the beginning of the first packet that enables the entire packet to be reassembled by the receiving system. In the teardrop attack, the attacker's IP puts a confusing offset value in the second or later fragment. If the receiving operating system does not have a plan for this situation, it can cause the system to crash.

• Smurf Attack: In this attack, the perpetrator sends an IP ping (or "echo my message back to me") request to a receiving site. The ping packet specifies that it be broadcast to a number of hosts within the receiving site's local network. The packet also indicates that the request is from another site, the target site that is to receive the denial of service. (Sending a packet with someone else's return address in it is called spoofing the return address.) The result will be lots of ping replies flooding back to the innocent, spoofed host. If the flood is great enough, the spoofed host will no longer be able to receive or distinguish real traffic.

• Viruses: Computer viruses, which replicate across a network in various ways, can be viewed as denial-of-service attacks where the victim is not usually specifically targeted but simply a host unlucky enough to get the virus. Depending on the particular virus, the denial of service can be hardly noticeable ranging all the way through disastrous.

• Physical Infrastructure Attacks: Here, someone may simply snip a fiber optic cable. This kind of attack is usually mitigated by the fact that traffic can sometimes quickly be rerouted.

 [WhatIs.com] 

DER (Distributed Energy Resources) - Distributed Energy Resources  [Common Usage]

Deregulation: The elimination of regulation from a previously regulated industry or sector of an industry.   [DOE Glossary of Electricity Terms]

DES: see Data Encryption Standard.

Device - A device is a physical entity connected to the communication network composed of at least one communication element (the network element), which may have a control element and/or a monitoring element.  [Common Usage]

Device Identity: The Device Identity, DI, contains the nameplate information of a device such as make, model, and serial number.  [Common Usage]

Device Model: A Device Model is an aggregation of Data Objects that together represent the communications visible functionality of a real device. [IEC61850]

Device: 1) In general, a device is a machine designed for a purpose. In a general context, a computer can be considered a device. 2) In the context of computer technology, a device is a unit of hardware, outside or inside the case or housing for the essential computer (processor, memory, and data paths) that is capable of providing input to the essential computer or of receiving output or of both.  [WhatIs.com]  A device is a physical entity connected to the communication network composed of at least one communication element (the network element), which may have a control element and/or a monitoring element.  [Common Usage]

DHCP (Dynamic Host Configuration Protocol): An TCP/IP protocol extension to BOOTP that dynamically allocates configuration information. Defined in RFC2131. See UDP/IP. See also RFC1534, RFC2132, RFC2241, RFC2485, RFC2563, RFC2610, RFC2855, RFC2937, RFC2939, RFC3004, RFC3011, RFC3046, RFC3118.

DHTML: See Dynamic HTML (DHTML)

Dial-Up Connection: This is a standard way of connecting to the Internet temporarily. Using a modem and special dial-in software, the computer establishes a connection with a remote server which itself is permanently connected to the Net.  [Common Usage]

Dialup line, dial-in line, dial line: A temporary data connection activated by establishing a direct-dialed telephone link between two communication devices. Compare with leased line.  [Common Usage]

Digital Certificate: See Certificate

Digital Signature: 1. A cryptographic modification of data that provides: (a) origin authentication, (b) data integrity, and (c) signer nonrepudiation (when associated with a data unit and accompanied by the corresponding public-key certificate). [After X9.49] 2. [A] cryptographic process used to assure message originator authenticity, integrity, and nonrepudiation. Synonym electronic signature. [INFOSEC-99] [T1 Glossary 2000: Glossary of Telecommunications Terms]  A digital code attached to an e-mail or other form of communication that assures the recipient of the authenticity of the sender.   [Common Usage]

Direct Access: The ability of a retail customer to purchase commodity electricity directly from the wholesale market rather than through a local distribution utility.   [DOE Glossary of Electricity Terms]

Directory:  A directory is, in general, an approach to organizing information, the most familiar example being a telephone directory. 1) On the World Wide Web, a directory is a subject guide, typically organized by major topics and subtopics. The best-known directory is the one at Yahoo (http://www.yahoo.com). Many other sites now use a Yahoo-like directory including major portal sites. 2) In computer file systems, a directory is a named group of related files that are separated by the naming convention from other groups of files. 3) In computer networks, a directory is a collection of users, user passwords, and, usually, information about what network resources they can access.  [WhatIs.com] 

Directory Service: A service on a network that uses a Directory to give information about sites, computers, resources, or users in the area. [Common Usage]

Disassembling: Converting a binary program into human-readable machine language.  [Common Usage]

DisCo: Distribution Company  [Common Usage]

Dispatch Order - Order issued by the dispatcher, concerning performance of the specific operations in the given electric facility. [Common Usage]

Distributed: Computing is said to be "distributed" when the computer programming and data that computers work on are spread out over more than one computer, usually over a network. Computing prior to low-cost computer power on the desktop, was organized in centralized "glass houses" (so-called because the computers were often shown to visitors through picture windows). Although these centers still exist, large and small enterprises over time are moving (distributing) applications and data to where they can operate most efficiently in the enterprise, to some mix of desktop workstations, local area network servers, regional servers, Web servers, and other servers. A popular trend has been client/server computing which is simply the view that a client computer can provide certain capabilities for a user and request others from other computers that provide services for the clients.   [WhatIs.com] 

Distributed Computing: In general, distributed computing is any computing that involves multiple computers remote from each other that each have a role in a computation problem or information processing. 1) In business enterprises, distributed computing generally has meant putting various steps in business processes at the most efficient places in a network of computers. In the typical transaction using the 3-tier model, user interface processing is done in the PC at the user's location, business processing is done in a remote computer, and database access and processing is done in another computer that provides centralized access for many business processes. Typically, this kind of distributed computing uses the client/server communications model.   [WhatIs.com] 

Distributed Computing Environment (DCE): In network computing, DCE (Distributed Computing Environment) is an industry-standard software technology for setting up and managing computing and data exchange in a system of distributed computers. DCE is typically used in a larger network of computing systems that include different size servers scattered geographically. DCE uses the client/server model. Using DCE, application users can use applications and data at remote servers. Application programmers need not be aware of where their programs will run or where the data will be located.  [WhatIs.com] 

Distributed Denial-of-Service (DDoS) Attack: On the Internet, a distributed denial-of-service (DDoS) attack is one in which a multitude of compromised systems attack a single target, thereby causing denial of service for users of the targeted system. The flood of incoming messages to the target system essentially forces it to shut down, thereby denying service to the system to legitimate users.  [WhatIs.com] 

Distributed Generation (DG): Electric generation facilities connected to an Area Electric Power System (EPS) through a Point of Common Coupling (PCC); DG is a subset of DR. [IEEE P1547 Standard for Interconnecting Distributed Resources with Electric Power Systems]

Distributed Resources (DR) or Distributed Energy Resources (DER): Sources of electric power that are not directly connected to a bulk power transmission system. DR includes both generators and energy storage technologies. [IEEE P1547 Standard for Interconnecting Distributed Resources with Electric Power Systems]

Distribution: The delivery of electricity to retail customers (including homes, businesses, etc.).   [DOE Glossary of Electricity Terms]

Distribution System: The portion of an electric system that is dedicated to delivering electric energy to an end user.   [DOE Glossary of Electricity Terms]

Distribution System Operator - Electric utility that holds license for transmission and distribution of energy, using the distribution network, in a part of the country that is identified in the license.  [Common Usage]

Divestiture: The stripping off of one utility function from the others by selling (spinning-off) or in some other way changing the ownership of the assets related to that function. Stripping off is most commonly associated with spinning-off generation assets so they are no longer owned by the shareholders that own the transmission and distribution assets.   [DOE Glossary of Electricity Terms]

DMS (Distribution Management System): used for managing the distribution assets and operations. DMS applications can include or not include many functions.  [Common Usage]

DMTF (Distributed Management Task Force): The DMTF is the industry organization that is leading the development, adoption and unification of management standards and initiatives for desktop, enterprise and Internet environments. http://www.dmtf.org

DMZ (DeMilitarized Zone): In computer networks, a DMZ (demilitarized zone) is a computer host or small network inserted as a "neutral zone" between a company's private network and the outside public network. It prevents outside users from getting direct access to a server that has company data. (The term comes from the geographic buffer zone that was set up between North Korea and South Korea following the UN "police action" in the early 1950s.) A DMZ is an optional and more secure approach to a firewall and effectively acts as a proxy server as well.  [WhatIs.com] 

DNP (Distributed Network Protocol): an RTU protocol based on the IEC 870-5 protocol standard, but modified for the North American market. See DNP Primer. [DNP Users Group]

DNS (Domain Name System): is a distributed database used by TCP/IP applications to map between domain names and IP addresses, and to provide electronic mail routing information. Defined in RFC1034 and RFC1035.  See also IANA and ICANN. The domain name system (DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address. Because maintaining a central list of domain name/IP address correspondences would be impractical, the lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority. There is probably a DNS server within close geographic proximity to your access provider that maps the domain names in your Internet requests or forwards them to other servers in the Internet.  [WhatIs.com] 

DNS Spoofing: Assuming the DNS name of another system by either corrupting the name service cache of a victim system, or by compromising a domain name server for a valid domain.

DoD: The U.S. Department of Defense who’s Advanced Research Projects Agency got the Internet started by creating the ARPAnet. [DoD]

DOM (Document Object Model): The Document Object Model (DOM) was developed by the W3C, and is a platform- and language-neutral interface that will allow programs and scripts to dynamically access and update the content, structure and style of documents. W3C's DOM is a standard API to the document structure and aims to make it easy for programmers to access components and delete, add or edit their content, attributes and style.  Hence, there are a number of domains DOM covers; e.g., DOM XML, DOM HTML (DOM Level 0), DOM Events, and DOM CSS.  The document can be further processed and the results of that processing can be incorporated back into the presented page. This is an overview of DOM-related materials here at W3C and around the web. [W3C Document Object Model]

Domain: An area of knowledge or activity characterized by a set of concepts and terminology understood by practitioners in that area. [OMG UML] In general, a domain is an area of control or a sphere of knowledge. In computing and telecommunication in general, a domain is a sphere of knowledge identified by a name. Typically, the knowledge is a collection of facts about some program entities or a number of network points or addresses. On the Internet, a domain consists of a set of network addresses. This domain is organized in levels. The top level identifies geographic or purpose commonality (for example, the nation that the domain covers or a category such as "commercial"). The second level identifies a unique place within the top level domain and is, in fact, equivalent to a unique address on the Internet (an IP address). Lower levels of domain may also be used.   [WhatIs.com] 

Domain Name: A unique name that identifies each computer on the Internet and is used in lieu of an IP address. Domain names are managed by IANA (Internet Assigned Numbers Authority) and ICANN (Internet Corporation for Assigned Names and Numbers).

Domain Type	Description
.com	Commercial business, organization, or company
.edu	Educational institution
.gov	Nonmilitary government entity
.int	International organization
.mil	Military organization
.net	Network administration, often Internet-related
.org	Other organizations: nonprofit, nonacademic
.uk, .au, ca, jp, se, etc.	Country codes denoting servers found in other countries. Complete country listing.

Domain Name System: See DNS.

Domain Type: Domain: A realm of control. On the Internet, there are several levels of domains each being a unique name for the collection of computers connected together in a unified network or networks. The top level domains consists of the two letter International country code such as .us, .ca (Canada), .au (Australia). Since the Internet was originated in the US, the 6 primary domains are not at this time required to indicate they belong in the US domain. The main domains in the US are .com, .org, .net, .edu, .gov, .mil. In each of those domains, there is another level of domains, normally controlled by a single organization.  [WhatIs.com] 

DoS: see Denial of Service

Dot Address: A dot address (sometimes known as a dotted quad address) refers to the notation that expresses the four-byte (32-bit) IP address as a sequence of four decimal numbers separated by dots. Each number represents the binary value of one of four bytes. Look at this Internet address, for example: 205.245.172.72. Tip:To find out the dot address (such as 205.245.172.72) for a given domain name, Windows users can go to their MS DOS prompt screen and enter: ping xxx.yyy where xxx is the second-level domain name like "whatis" and yyy is the top-level domain name like "com").  [WhatIs.com] 

Double-Circuit Line: two three-phase circuits for electric power transmission constructed on a single structure. (NERC "Terms and Their Definitions As Used in the NERC Planning Standards")

Download: To transfer a copy of a file residing on a remote computer to a user's computer.  [T1 Glossary 2000: Glossary of Telecommunications Terms]   Downloading is the transmission of a file from one computer system to another, usually smaller computer system. From the Internet user's point-of-view, to download a file is to request it from another computer (or from a Web page on another computer) and to receive it.  [WhatIs.com]   The opposite is to upload.

DR (Distributed Resources):  See Distributed Resources.

Driver: Software for using a peripheral hardware device attached to a computer.

Droop of Generating Unit Control: [603-04-08] Ratio of the per-unit change in frequency to the per-unit change in power. [IEC_Glossary_1929b.pdf]

DS-0: In T-carrier, a basic digital signaling rate of 64 kb/s, corresponding to the capacity of one voice-frequency-equivalent channel. Note 1: The DS0 rate forms the basis for the North American digital multiplex transmission hierarchy. Note 2: The DS0 rate may support twenty 2.4-kb/s channels, or ten 4.8-kb/s channels, or five 9.67-kb/s channels, or one 56-kb/s channel, or one 64-kb/s clear channel.  [T1 Glossary 2000: Glossary of Telecommunications Terms] 

DS-1: Digital Signal (DS) Service, level 1. Provides a digital signaling rate of 1.544 Mbps, which is implemented using a T-1 line.  [T1 Glossary 2000: Glossary of Telecommunications Terms] 

DS-2: Digital Signal (DS) Service, level 2. Provides a digital signaling rate of 6.312 Mbps which is implemented using a T-2 line.  [T1 Glossary 2000: Glossary of Telecommunications Terms] 

DS-3: Digital Signal (DS) Service, level 3. Provides a digital signaling rate of 44.736 Mbps which is implemented using a T-3 line.  [T1 Glossary 2000: Glossary of Telecommunications Terms] 

DS-4: Digital Signal (DS) Service, level 4. Provides a digital signaling rate of 274.176 Mbps which is  implemented using a T-4 line.  [T1 Glossary 2000: Glossary of Telecommunications Terms] 

DSL, see xDSL.

DSM (Demand Side Management) - Customer measures to reduce or shift load. These measures can be performed voluntarily by the customer or could be performed by the distribution company in accordance with the customer's tariff. For residential customers, DSM can include cycling water heaters, air conditioners, and pool pumps. For commercial and industrial customers, DSM can involve the turning off of specific machinery or other energy saving steps. Typical reasons for DSM are peak shaving, emergency situations, and market prices.  [Common Usage]

DTD (Document Type Definition): A Document Type Definition (DTD) is a specific document defining and constraining definition or set of statements that follow the rules of the Standard Generalized Markup Language (SGML) or of the Extensible Markup Language (XML), a subset of SGML. A DTD is a specification that accompanies a document and identifies what the funny little codes (or markup) are that, in the case of a text document, separate paragraphs, identify topic headings, and so forth and how each is to be processed. By mailing a DTD with a document, any location that has a DTD "reader" (or "SGML compiler") will be able to process the document and display or print it as intended. This means that a single standard SGML compiler can serve many different kinds of documents that use a range of different markup codes and related meanings. The compiler looks at the DTD and then prints or displays the document accordingly. [WhatIs.com] 

DTE (Data Terminal Equipment): In computer data transmission, DTE (Data Terminal Equipment) is the RS-232C interface that a computer uses to exchange data with a modem or other serial device. For further information about the DTE interface and its relationship to the Data Communication Equipment (DCE) interface, see RS-232C.  [WhatIs.com] 

Duplex: see Full Duplex Mode

DXF (Drawing Exchange Format) or (Data Exchange File): A two-dimensional graphics file format supported by virtually all PC -based CAD products. It was created by Autodesk for the AutoCAD system. [Webopedia]

Dynamic HTML (DHTML): Dynamic HTML is a collective term for a combination of new Hypertext Markup Language (HTML) tags and options, that will let you create Web pages more animated and more responsive to user interaction than previous versions of HTML. Much of dynamic HTML is specified in HTML 4.0. Simple examples of dynamic HTML pages would include (1) having the color of a text heading change when a user passes a mouse over it or (2) allowing a user to "drag and drop" an image to another place on a Web page. Dynamic HTML can allow Web documents to look and act like desktop applications or multimedia productions.   [WhatIs.com] 

Dynamic Instability (of a power system): Lack of damping which results in a build-up of oscillations in the power system, and may or may not lead to loss of synchronism. NOTE – Under this condition the derivative of active power with respect to rotor speed is negative for at least one generator.   [IEC_Glossary_1929b.pdf]