D

DA Destination MAC Address

DAC (Dual Attached Concentrator; also digital-to-analog converter) A device that is attached to and allows access to both rings in an FDDI network.

DANTE Delivery of Advanced Network Technology in Europe - an organisation based in Cambridge, England. For more information see the DANTE web site.

DAS (Dual-Attached Station) A station with two connections to an FDDI network, one to each logical ring. If one of the rings should fail, the network automatically reconfigures to continue normal operation.

DASD Direct Access Storage Device

Data flow control layer Layer 5 of the SNA architectural model.

Data link control layer Layer 2 in the SNA architectural model.

DCE (Data Communications -- or Data Circuit- terminating --Equipment) A communications device that can establish, maintain and terminate a connection (for example, a modem). A DCE may also provide signal conversion between the data terminal equipment (DTE) and the common carrier's channel. Contrast DTE.

D-Channel D-Channels are the 16 Kbps (basic rate) or 64 Kbps (primary rate) full duplex ISDN signaling channels which carries messages between the customer equipment and the public switch. Messages can communicate call request information (phone numbers) and incoming call information, for example.

DDS Digital Data Service

DECNet* Digital Equipment Corporation's proprietary network architecture.

Dedicated line A transmission circuit installed between two sites of a private network and "open," or available, at all times.

Default route Entry in a routing table that can re-direct any frames for which the table has no definitive listing for the next hop.

Delay Amount of time a call spends waiting to be processed.

Demodulation Opposite of modulation; the process of retrieving data from a modulated carrier wave.

DES Data Encryption Standard - an encryptian scheme approved for use within the US by the National Security Agency (NSA).

Designated router In OSPF, each multiaccess network with at least two attached routers has a designated router. The designated router has special duties in the running of the protocol, such as generating a link state advertisement for the multiaccess network. This concept helps reduce the number of adjacencies required on a multiaccess network, which cuts routing protocol traffic and the size of the topological database.

Dial up A type of communication that is established by a switched-circuit connection using the telephone network.

Digital modem: A digital modem accepts an analog call over a 64 K bit ISDN channel and interprets it via software as a call originated by an analog modem. This process generally requires the use of a DSP to break the analog signal into an equivalent digital bit stream.

DLC (Data Link Control) The SNA layer responsible for transmission of data between two nodes over a physical link.

DLCI (Data Link Connection Identifier) A value in frame relay that identifies a logical connection.

DLSw Data Link Switching It is a method of encapsulating, or tunneling, Logical Link Control Type 2 (LLC2) packets from LAN-based SNA and NetBIOS applications, enabling them to traverse a non-SNA backbone. Specified in FRC 1434.

DLCX Data Link Control Exchange

DLUR/DLUS Dependent LU Requester/Dependent LU Server

DMA Direct Memory Access

DMA Distributed Management Architecture

Domain (Domain Name) Part of the DNS naming hierarchy which identifies a particular network or sub-network. The unique address that identifies a network or Internet site consist of two or more domains, separated by dots, starting with the most specific and ending with the most general. Any given network may have more than one Domain Name, but any one Domain Name can only apply to one network.

DNS Domain Name System, maps Internet Protocol addresses to named computers via a set of distributed databases which are automatically updated.

DPA Demand Protocol Architecture

DPAM Demand Priority Access Method

DQDB (Distributed Queue Dual Bus) Communication protocol proposed by IEEE 802.6 committee for use in MANs.

DRA Distributed Repeater Architecture

DRI (Distributed Recovery Intelligence) The ability to track down a network problem and automatically isolate the malfunctioning node.

Drop cable A cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from the network node to a transceiver (a transmit/receiver) attached to the trunk cable. Compare AUI cable.

DS (Digital Signal) Standard specifying the electrical characteristics for data transmission over four-wire telco circuits. DS1 is 1.544 Mbps and DS3 is 44.736 Mbps. Also referred to as T1 and T3.

DS-1 Digital (transmission) System 1, or Digital Signal level 1; refers to the 1.44 Mbps (U.S.) or 2.108 Mbps (Europe) digital signal carried on a T1 circuit.

DS-3 Digital (transmission) System 3, or Digital Signal level 3; refers to the 44 Mbps digital signal carried on a T3 circuit.

DSP A digital signal processor (DSP) is a CPU that is tailored to handle complex mathematical functions.

DSPU Downstream Physical Unit

DSU/CSU (Data service unit/channel service unit) A data service unit/channel service unit connects an external digital circuit to a digital circuit on the customers premises. The DSU converts data into the correct format, and the CSU terminates the line, conditions the signal, and participates in remote testing of the connection.

DTE (Data Terminal Equipment) End-user equipment, typically a terminal or computer, that can function as the source or destination point of communication on the network. Contrast DCE.

DTR Data Terminal Ready (modems)

DTR Dedicated Token Ring

Dual-attached servers Servers attached to both paths of an FDDI ring for load balancing and redundancy.

Dual homing Method used to connect a DAS or DAC to a pair of concentrators on an FDDI ring; used when server or station availability is critical in a network.

DXI Data Exchange Interface Allows a DTE (such as a router) and a DCE (such as an ATM DSU) to provide an ATM UNI for networks.

Dynamic Bandwidth Allocation: The ability to add and drop B channels based on the sending of threshold data levels. Specifically, the ability to raise a call over a 2nd B channel when the first B channel becomes saturated and to drop the call when data rates decline.

Dynamic routing Routing that adjusts automatically to changes in network topology or traffic.