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  • Darpa (Defense Advanced Research Projects Agency) Formerly called Arpa, this US government agency that funded research and experimentation with the Arpanet and later, the connected Internet- The group within Darpa responsible for the Arpanet is ISTO (information Systems Techniques Office), formerly IPTO (Information Processing Techniques Office).
  • DassiII A message based signaling system following the ISO based model developed by BT to provide multi-line IDA interconnection to the BT network.
  • Data compression A way of reducing the amount of data to be transmitted by applying one of severs techniques that reduce the number of bits needed to represent the information. When the data is received It is decompressed into its original form.
  • Database server A database installed as a back-end or server component of a client-server system, which can be accessed over a LAN by one or more client, or front-end applications through the use of query language, typically SQL. The server part of the program is responsible for updating the records, ensuring that multiple access is available to authorized users, protecting the data and communicating with other servers holding relevant data. The client end of the program requests records and then modifies them, while the server tracks records down for the client and adds new ones.

  • Datagram A method of sending data in which parts of the message are sent in random order. The recipient machine has the task of reassembling the parts in the correct sequence. The datagram is a connectionless, single packet message or item of data that can traverse a network at OS I Level Three, the Network Layer. It typically does not involve end-to-end session establishment or delivery-confirmation acknowledgment. As well as the information within the datagram, there is a destination network address and usually a source network address.
  • Data link A direct serial data communications path between two devices without intermediate switching nodes.
  • Data Link Layer Layer Two of the ISO OSI model is responsible for the transmission of information over a physical medium. After establishing the link it ensures the error-free delivery of the information through the use of error detection, error recovery and flow control. The contention access methods such as CSMA/CD and Token passing are Layer Two activities.
  • Data PBX A switching system for data traffic that allows terminals and workstations connected by individual cables to the Data PBX selectively to link to one or more host computers over asynchronous circuits through the use of contention.
  • DCA (Defense Communication Agency) The US government agency responsible for the installation of Defense Data Networks, like Arpanet and Milnet, and PSNs. The DCA writes contracts for operation of the DDN and pays for network services.
  • DCA (Document Content Architecture) The IBM approach to storing documents as two types of document group: draft documents and final form documents. For presentation, the draft document is transformed into a final document through an office system.
  • DCE (Data Circuit Terminating Equipment) Communications equipment installed in a user's premises responsible for establishing, maintaining and terminating a connection. A modem is an example.

  • DCE (Distributed Computing Environment) A suite of software utilities and operating system extensions that will, in theory, create applications on networks of heterogeneous hardware - PCs, Unix workstations, minicomputers and mainframes. The DCE is the product of the OSF. The DCE is designed to simplify the building of heterogeneous client/server applications and provides seven general services: Remote Procedure Call, Security, Naming (directory), Distributed File System, Threads, Time and PC Integration. DDE (Dynamic Data Exchange) - A Microsoft messaging specification. When DDE-compliant applications are combined, dynamic documents can be created which update each other as data changes.

  • DDE Dynamic Data Exchange, Microsoft's protocol to communicate between Windows applications
  • DDM (Distributed Data Management Architecture) An IBM SNA LU 6.2 transaction providing users with facilities to locate and access data in the network. It involves two structures: DDM Source, and DDM Target. The Source works with a transaction application to retrieve distributed data and transmits commands to the Target program on another system where the data that has been requested is stored. The Target interprets the DDM commands, retrieves the data and sends it back to the Source that originated the request.
  • DDCMP (Digital Data Communication Message Protocol) The DecNet- specific Link Level protocol that operates at Layer Two of the Digital Network Architecture.
  • DDN (Defense Data Network) Used generally to refer to Milnet, Arpanet and the TCP/IP protocols those networks use. More specifically refers to Milnet and associated parts of the connected Internet that connect military installations.
  • DecNet Proprietary peer-to-peer network technology originally developed for use in wide area networking by the Digital Equipment Corporation (Dec) and evolved to include significant Ethernet-based LAN capabilities. It is the implementation of the Digital Network Architecture (DNA).
  • Dect (Digital European Cordless Telecommunications) A standard governing pan-European digital mobile telephony. Based on advanced TDMA technology, Dect covers cordless PBXs, telepoint and residential cordless telephony.
  • Demand Priority Access method providing support for time-sensitive applications such as video and multimedia as part of the proposed 100BaseVG standard offering l00Mbit/s over voice-grade UTP cable. By managing and allocating access to the network centrally, at a hub rather than from individual workstations, sufficient bandwidth for the particular application is guaranteed on demand. Users, say its proponents, can be assured of reliable, continuous transmission of information.

  • Demodulation Technique for retrieving information from a modulated signal. Demonstrated by the eponymous modem (modulator/demodulator).
  • Des (Data Encryption Standard) An algorithm designed by the US National Bureau of Standards for the encryption and de-encryption of data using a 64-bit key.
  • Device driver In the context of computer networking a device driver is a software module forming part of a computer operating system, or software that interacts with the operating system. It aims to control communications equipment, such as a LAN network adapter card and facilitate the transfer of information to and from the network. Other examples of device driver programs include software to support the activities of printers, disks and mice.
  • DIA (Document Interchange Architecture) An IBM term defining the sets of functions needed for document handling in an IBM environment, including storage and distribution.
  • Digital signal A signal with only two values, normally 0 and 1, during transmission, unlike an analog signal whose values constantly vary.
  • DIMM (dual in-line memory module) A DIMM has a lot more bandwidth than a single in-line memory module (SIMM). It's a small circuit board filled with RAM chips, and its data path is 128 bits wide, making it up to 10 percent faster than a SIMM.
  • DIMM PC Sub-credit card size PC that uses the DIMM plug interface
  • Direct attachment The IBM term for linking a device or LAN directly to a host computer through an appropriate Control Unit, like a cluster controller.
  • Disk server A device equipped with disks and a program permitting users to create and store files on those disks. Each user has access to their own section of disk on the disk server. The aim is to give users access to disk space that they would not normally have on their PC. The disk server is linked to the PCs via a LAN. The next level of sophistication would be a file server.
  • Diskless workstation A PC or workstation attached to a LAN that has neither floppy nor hard disks, but relies on disk storage provided by a file server attached to the same LAN. When the diskless workstation is first initialized it uses a remote boot program stored in a remote boot prom/eprom on its network adapter card to initialize a session with the file server. The workstation then loads its operating system, such as MS-Dos, from the server and executes the normal server login procedure.
  • Distributed database A database stored on more than one networked computer. The database is split up across these machines, and not replicated.

  • Distributed name service A technique for storing network node names so that the information is stored throughout the network, and can be requested from, and supplied by, any node.
  • Disoss (Distributed Office Support Systems) IBM software typically forming part of an IBM Office System Node.
  • Distributed computing The trend away from having big, centralized computers such as mini-computers and mainframes to bring processing power to the desk top. Often confused with distributed processing.
  • Distributed processing An approach that allows one application program to execute on multiple computers linked together by a network. The networked computers share the work between them.
  • DLS (Data Link Switching) An enhancement to source routing which transports source route packets over a resilient IP/OSPF network and provides local termination of LLC2 sessions to avoid LLC timeouts in large or busy networks. It is the ideal mechanism for mixed LAN-to-LAN and interactive SNA traffic since it can recover from network problems quickly using OSPF. It is rapidly becoming accepted as a major standard.
  • DMA (Direct Memory Access) A technique for high-speed data transfer between a device such as LAN network adapter card and the computer memory. DMA bypasses the Central Processing Unit of the computer, PC or workstation, allowing the device to transfer a block of information directly across the bus into system memory.
  • DMI (Desktop Management Interface) A set of APIs outlined by the DMTF, comprising three components: service layer, component interface and management interface.
  • DNA (Digital Network Architecture) The network architecture of Digital Equipment Corporation with eight layers. The DNA is similar in structure to OSI at lower levels, except that the top three layers of the DNA correspond to the top two layers in the OSI model.
  • DNS (Domain Name System) The online distributed database system used by Internet to map names into IP addresses. DNS servers throughout the connected Internet implement a hierarchical namespace that allows sites freedom in assigning machine names and addresses. DNA also supports separate mappings between mail destinations and IP addresses.

  • Domain A group of nodes on a network that form an administrative entity. It could also be a number of servers grouped together and named to simplify network administration and security. Every computer on the LAN belongs to at least one domain. Being logged in on one domain, however, does not limit resources in other domains to which the user has access permissions.
  • Dos - Disk Operating System comprising one or a suite of programs managing a disk-based computer system. Dos schedules and supervises work, allocating computer resources and the operation of peripherals. Versions of Dos from different vendors exist: Microsoft's MS-Dos is the most common. Dos 3.1 was the first version of MS and PC Dos able to support LAN functions separate, of course, from the network's own operating system - notably including record and file locking which is now standard on multi-user systems.
  • Dos LAN Manager A Dos version of Microsoft's network operating system LAN Manager. It gives Named Pipes (an applications interface) support to Dos machines, enabling them to use the client/server environment.
  • Downlink Transmission from a satellite to an Earth Station.
  • DPA (Demand Protocol Architecture) A technique for loading protocol stacks dynamically as they are required. It is associated with adapter cards in workstations and servers. Only the protocol stacks that are needed for a particular communications sessions are loaded. Examples of stacks that could be loaded include TCP/IP, XNS, SPX/IPX and NetBios.
  • DPNSS (Digital Private Networks Signaling System) Signaling standard for digital private networks within the UK formulated jointly by BT and PABX manufacturers.
  • DQDB (Distributed Queue Dual Bus) The standard for future Mans which operates as a dual bus, each carrying data in both directions. A queuing system maintains transmission order. Some similarity with ATM encourages evolution between the technologies.
  • Drop cable A cable that links a network adapter to an external transceiver attached to a co-axial LAN such as Ethernet. Also called an Attachment Unit Interface cable or transceiver cable.
  • DS1 (Digital Signal 1) Transmission standard at T1 speeds, or 1.544Mbit/s

  • DS3 (Digital Signal 3) Transmission standard at T3 speeds, or 44.736Mbit/s. DS3 allows the combination of 28 DSls or a single DS3 facility - also known as a T3 circuit.
  • DSE (Digital Switching Exchange) A node in a telecommunications network.
  • DSU (Data Service Unit) Data transmission equipment used to interface to a digital circuit at customer site. It converts the customer's datastream, such as X.21 to E1 or T1 for transmission through the CSU, which is often contained, functionally within the DSU device. DSUs can convert data to or from a native port on a router to an E1, E2 or E3 leased line, primary rate ISDN or SMDS, DSU functionality can be built into devices such as some routers or multiplexers. In Europe a DSU can convert El bandwidth into RS.449, X.21, V.35 or other serial interface via a router. A DSU with an HSSI interface will deliver E2 or E3 bandwidth from the WAN to an HSSI router on a LAN.
  • DTE (Data Terminal Equipment) A piece of equipment where a communications path ends. The user's equipment is collectively termed DTE and can include PCs and display terminals.
  • DTMF (Dual Tone Multi-Frequency) A term for push button or Touchtone (an AT&T trademark) dialing. The pushed button makes a tone, actually the combination of two tones - of high and low frequency. They are necessary to access advanced network features such as call barring and call forwarding. DTMF penetration in the mass-market the UK is small but growing, but high in the business community.
  • Duplex Simultaneous, two-way independent transmission of data.
  • Dynamic node address An Apple-patented feature of AppleTalk under which each node assigns itself a unique address code each time it is initialized. Conventionally, nodes are assigned fixed addresses that do not change.
  • Dynamic routing A process for selecting the most appropriate path or route for a packet or datagram to travel around a network. At the end of each leg of the journey of the packet across the network the router decides on the most appropriate path for the packet or datagram to follow if there are multiple routes available. This is done using network status information gathered from around the Internet and passed from router to router through the use of routing information protocols.

The Net is the Automation.
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composed by JohnBlack '01

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