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Glossary
1 8 A B C D E F G H I J L M N O P Q R S T U V W
D
  • data integrity

Refers to the validity of data. Data integrity can be compromised in a number of ways:

  • Human errors when data is entered
  • Errors that occur when data is transmitted from one computer to another
  • Software bugs or viruses
  • Hardware malfunctions, such as disk crashes
  • Natural disasters, such as fires and floods

There are many ways to minimize these threats to data integrity. These include:

  • Backing up data regularly
  • Controlling access to data via security mechanisms
  • Designing user interfaces that prevent the input of invalid data
  • Using error detection and correction software when transmitting data
  • Data Link Layer

Layer 2 of the OSI model. The entity, which establishes, maintains, and releases data-link connections between elements in a network. Layer 2 is concerned with the transmission of units of information, or frames, and associated error checking.

  • datagram

A datagram is a basic transfer unit associated with a packet-switched network in which the delivery, arrival time, and order of arrival are not guaranteed by the network service.
 

  • Datagram Congestion Control Protocol

DCCP, short for Datagram Congestion Control Protocol, is a minimal general purpose transport-layer protocol that minimizes the overhead of packet header size or end-node processing as much as possible. DCCP provides the establishment, maintenance and teardown of an unreliable packet flow, as well as the congestion control of that packet flow.

  • dB

Decibel
A unit used to measure relative increase or decrease in power, voltage or current, using a logarithmic scale.

  • dBm

A measure of power in communications: the decibel in reference to one milliwatt (0 dBm = 1 milliwatt and -30 dBm = .001 milliwatt).

  • DCD

Data and Carrier Detect
A modem interface signal indicating to an attached terminal that the local modem is receiving a signal from the remote modem.

DCE is a popular choice for very large systems that require robust security and fault tolerance.

2.      Short for Data Communications Equipment, a device that communicates with a Data Terminal Equipment (DTE) device in RS-232C communications. See DTE for more information.

  • Decibel

A unit used to measure relative increase or decrease in power, voltage or current, using a logarithmic scale.

  • decryption

The process of decoding data that has been encrypted into a secret format. Decryption requires a secret key or password.

  • defacement

In Web site security terminology, the word defacement is most often used to describe the changing or defacing of a Web page or Web site by an unauthorized individual or process, usually a hacker

  • default gateway

1.      The gateway in a network that a computer will use to access another network if a gateway is not specified for use.

2.      In a network using subnets, the router that forwards traffic to a destination outside of the subnet of the transmitting device.

  • DES

Short for Data Encryption Standard, a popular symmetric-key encryption method developed in 1975 and standardized by ANSI in 1981 as ANSI X.3.92. DES uses a 56-bit key and uses the block cipher method, which breaks text into 64-bit blocks and then encrypts them.

  • DHCP

Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.
Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users.

  • DiffServ

QoS method to differentiate and control IP traffic so that the traffic’s relative priority can be determined on a per-hop basis.

  • Digital

The binary (“1” or “0”) output of a computer or terminal. In data communication, an alternating, non-continuous (pulsating) signal.

  • Digital Loopback

A technique for testing the digital processing of a communications device. The loopback is toward the line side of a modem, but tests most of the circuitry in the modem under test.

  • Distortion

The unwanted change in a signal’s waveform occurring between two points in a transmission system.

 

  • Dry Contact Alarms

Contact pins on a connector are closed or opened to indicate alarms. External alarm monitoring equipment uses the change in current flow across these pins to set off an alarm.

  • DSL

Digital Subscriber Line
A modem technology for transmitting information at high speeds on existing copper phone lines to homes and businesses. DSL operates over existing copper telephone lines and requires runs of usually less than 20,000 feet to a central telephone office. Types of DSL include asymmetric DSL (ADSL), symmetric DSL (SDSL), high-bitrate DSL (HDSL) and the latest, symmetric high-bitrate DSL (SHDSL).

  • DSU

Digital Service Unit
A user device interfacing to a digital circuit (such as DDS or T1 when combined with a CSU). The DSU converts the user’s data stream to bipolar format for transmission.

  • DTE

Data Terminal Equipment
As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, such as personal computers, data terminals or printers. DTE refers to application equipment, such as a videoconference terminal or LAN bridge or router, while DCE refers to equipment such as network access equipment.

  • DTMF

Dual-Tone Multifrequency
DTMF is a technology enabling a touch-tone telephone to create 16 tones using frequencies.

  • DTR

Data Terminal Ready
A modem interface control signal sent from the DTE to the modem, usually telling the modem that the DTE is ready to transmit data.

  • DVMRP

The Distance Vector Multicast Routing Protocol (DVMRP), defined in RFC 1075, is a routing protocol used to share information between routers to facilitate the transportation of IP multicast packets among networks. It formed the basis of the Internet's historic multicast backbone, Mbone.