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Glossary Section "D" ( Definitions )

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0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

D4 The older an probably most common framing pattern for T1 circuits. Eight bits from each of the twenty four DS0's are put together to form a frame, then a framing bit is added to the end of each frame.

D-channel The ISDN channel that carriers signaling information to control the call setup, teardown, or invocation of supplementary services. The D-Channel may also be used to provide packet mode data service.

DACS Digital Access and Cross-connect System is equipment that allows control of individual DS0 s in a DS1 data stream. This unit allows an individual DS0 to be mapped from one DS1 to a specific DS0 position on another DS1.

DAP Directory Access Protocol. The protocol used between a Directory User Agent (DUA) and a Directory System Agent (DSA) in an X.500 directory system. See LDAP.

datagram 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. See frame, packet.

Data Link Layer The OSI layer that is responsible for data transfer across a single physical connection, or series of bridged connections, between two Network entities.

DB-9 A nine pine physical connector common on PCs and a secondary connector specified in RS-449. picture

DBU Dial Backup Unit

DC Direct Current. The positive side remains positive and the negative side remains negative as in a battery.

DCA Defense Communications Agency. The government agency responsible for the Defense Data Network (DDN). See DISA

DCC Data Communications Channel

DCE Data Communications Equipment. Any device attached to the communications line that manipulates a transmitted signal

DCE Distributed Computing Environment. An architecture of standard programming interfaces, conventions, and server functionality's (e.g., naming, distributed file system, remote procedure call) For distributing applications transparently across networks of heterogeneous computers. Promoted and controlled by the Open Software Foundation (OSF)-now part of The Open Group-a vendor consortium.

DCLU Digital Carrier Line Unit

DCME Digital Circuit Multiplication Equipment is a term used with voice compression applications. By compressing voice traffic a DCME can transport much more cost effectively.

DCS Digital Cross connect System

DCOM Distributed Component Object Model. A 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 Internet protocols such as HTTP.

DDN Defense Data Network. Comprises the MILNET and several other DoD networks

DDS Dataphone Digital Service. AT&T private line service for transmitting data over a digital system. The digital transmission system transmits electrical signals directly, instead of translating the signals into tone of varied frequencies as with traditional analog transmission systems. Digital techniques provide more efficient use of transmission facilities, resulting in lower error rates and costs than analog systems.

DDS-I Dataphone Digital Service

DDS-II Dataphone Digital Service with a side channel

DECnet Digital Equipment Corporation's proprietary network architecture.

default route A routing table entry which is used to direct packets addressed to networks not explicitly listed in the routing table.

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

DES Data Encryption Standard. A popular, standard encryption scheme. See PGP, RSA.

DF Distributing Frame

DF1 An Allen-Bradley open protocol for serial communication.

DHCP Dynamic Host Configuration Protocol. A protocol which allows a host to obtain configuration information, such as its IP address and the default router from a server. This simplifies network administration because the software keeps track of IP addresses. With DHCP device can have a different IP address every time it connects to the network. It is frequently used by ISPs.

dial-up A dialup line is a circuit that exists between two nodes that uses the switched telephone network.

DID Direct Inward Dialing is a service provided by your local phone company that allows you to have a larger number of phone numbers than actual lines. These DID numbers can be routed by a PBX to go to an individual work station. For example if you had 50 work stations but only 50% of those are staffed at any one time, and you estimated that only 20% of the staff would be using the phone at one time, you can reduce the number of actual incoming lines to 10. There is a savings in that you now only have 10 actual phone lines but you have 50 different phone numbers (one for each work station). You are however limited to 10 active calls at one time.

digital hub Designated office where DDS channels are inter-connectand where synchronous network timing, testing access, and additional service features are provided.

DIMM A Dual In-line Memory Module is a memory chip with a 64-bit data path. Generally speaking one DIMM will replace the functionality of two SIMMs.

DIP switches enable you to configure a device without an external terminal. DIP switches always toggle. They are either "on" or "off". DIP also, means "Dual In line Package".

DISA Defense Information Systems Agency. The new name for DCA. See DCA

DIT Directory Information Tree. The global tree of entries corresponding to information objects in the OSI X.500 Directory.

DIY Do It Yourself. Network shorthand. See IMHO, BTW

DLC Digital Loop Carrier is the local loop infrastructure that connects customers located more than 18,000 feet from the central office.

DLL Dynamic  Library Link is a  small program called by a larger program  as needed. Typically, the small program that lets the larger program communicate with a specific device such as a printer or scanner.

DLSw Data Link Switching. A reliable means of transporting SNA and NetBIOS traffic in a multi-protocol router network using IP encapsulation. Defined in RFC1434 and RFC 1795.

DLTU Digital Line Trunk Unit

DM Delay Measurement

DMS Digital Multiplex Equipment

DN Distinguished Name. The global, authoritative name of an entry in the OSI Directory (X.500).

D-NFV Distributed Network Functions Virtualization

DNP3 Distributed Network Protocol is a set of communications protocols intended to insure interoperability between substation outstations and master stations for the electric utility industry. It is also widely used in the oil and gas industry.

DNS Domain Name System. The distributed name/address mechanism used in the Internet. The DNS maps a name like "polaris.interop.com" to its IP address Reverse lookup from the IP address to the name is also possible using the DNS.

DOCSIS Data Over Cable Service Interface Specification

domain In the Internet, a part of a naming hierarchy. Syntactically, an Internet domain name consists of a sequence of names (labels) separated by periods (dots), e.g., "msn.com" In OSI, "domain" is generally used as an administrative partition of a complex distributed system, as in MHS Private Management Domain (PRMD), and Directory Management Domain (DMD).

dotted decimal notation The 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 in the Internet as in: Also called "dotted quad notation."

DQDB Distributed Queued Dual Bus

DS-1 1.544Mbit/s.24 voice. T-1 system. Usually wire.

DS-1C An enhancement to T1 allowing 3.152 Mbit/s.

DS-0 A single voice signal in a digital from takes 64,000 bit/s. 1 voice.

DS-2 6.312 Mbit/s. 96 voice. T-2 system. Usually cable.

DS-3DS3 44.736 Mbit/s 672 voice. T-3 system. Microwave or Optical Fiber

DS-4 274.176 Mbit/s. 4032 voice, T-4 system. Optical fiber.

DSA Directory System Agent. The software that provides the X.500 Directory Service for a portion of the directory in Formation base. Generally, each DSA is responsible for the directory information for a single organization or organizational unit.

DSL Digital Subscriber Line. There are five versions of DSL. HDSL, SDSL, ADSL, RADSL,  and VDSL.

DSLAM Digital Subscriber Line Access Multiplexer This device is generally found at the Telco terminating multiple DSL lines.

DSU Digital Service Unit. A component of customer premise equipment used to interface to a digital circuit (DDS or T1); combined with a channel service unit (CSU), it converts a customer's data stream to bipolar format for transmission. See CSU.

DSU/CSU A device which includes the CSU and the DSU in the same unit.

DSVD A technology patented by Multi-Tech, which lets you simultaneously talk and send data over one analog line.

DSX-1 Digital Cross-connect, level 1.  A point where DS1 signals are cross connected between equipment. This could be at a CO, POP, or PBX connection.

DT Dial Tone

DTE Data Terminal Equipment. Any digital device such as a terminal, printer, or computer that transmits and receives data.

DTMF Dual Tone Multi Frequency. (Also known as Touch Tone TM). DTMF is used for dialing and for communicating with interactive telephone systems such as voice mail. It uses two tones to represent each key on the telephone touch pad. The tones are presented in a matrix of rows and columns. When any key is pressed the tone of the column and the tone of the row are generated, hence dual tone. As an example, pressing the "5" (second column, second row) button generates the tones 770Hz and 1336 Hz.

DTT Direct Trunk Transport

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

DVMRP Distance-Vector Multicast Routing Protocol. DVMRP is a distance-vector routing protocol designed to support the forwarding of multi-cast datagrams through an internetwork.

DWDM DWDM Dense Wavelength Division Multiplexing  allows for multiple signals to be sent simultaneously over a fiber by having each of those signals on a different wavelength. This technology significantly increases the amount of data that can be passed over the fiber.

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.

Dying Gasp is feature that enables a device to store a small amount of power to enable it to send out a SNMP trap to alert a management station in the event of a power failure.

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