[D]

D4 framing format – (1) Division of DS1-level circuit into 24 equal channels. [Each channel carrier digitizes voice and signaling information in eight-bit bytes. A D4 frame consists of 192 (8 X 24) information bits. In addition, to identify each of the 24 channels, a framing bit is added in the 193rd position. Each byte is updated 8,000 times per second. Thus, the transmission speed of a DS1 circuit is 1,544,000 Hz (193 X 8,000).] (2) Monitors the DS1 signals for either framing errors or bipolar violations (BPVs). BPVs are eliminated when the bit stream passes through interfaces such as a multiplexer, Automatic Protection Switch or the Digital Cross-Connect System (DCS). Since no end-to-end performance monitoring is available using BPVs, the line must be taken out of service to test for large errors.

Daisy chain – Connection of multiple devices in a serial fashion. [An advantage of daisy chaining is a savings in transmission facilities. The disadvantage is that if a device malfunctions, all other devices daisy-chained behind it are disabled.]

Data – (1) Units of information. (2) Any representation, such as characters or analog quantities, to which meaning is or may be assigned.

Data above voice (DAV) – Transmission system which carries digital data on a portion of the microwave radio spectrum above the frequency used for voice transmission.

Data access arrangement (DAA) – Communication equipment furnished by a common carrier that allows attachment of privately owned data transmission equipment (DTE) to the common carrier network.

Data communications – (1) Transfer of information between a source and a destination via one or more data links, according to appropriate protocols. (2) Transmission and reception of data, often including operations such as coding, decoding and validation.

Data conversion – Process of changing information from one form of representation to another.

Data coupler – A device to connect customer-owned modems or data sets to the regular telephone network. It functions by limiting the power applied to the line and providing network control and signaling.

Data encryption standard (DES) - A cryptographic algorithm designed by the National Bureau of Standards to encipher and decipher data using a 64-bit key.

Data pbx – A digital switch that allows a user on an attached circuit to select from other circuits, usually one at a time and on a contention basis, for the purpose of establishing a through connection. [A data PBX is distinguished from a PBX in that only digital transmission, and not analog, is supported.]

Database – An organized compilation of computerized bits. [Formalized rules exist for the establishment, control and access of a database.]

Datalink control – Second layer in the International Standards Organization reference model for Open Systems Interconnection (OSI). Synonym: protocol.

Datapac Network – A common user, packet-switched data network provided by The Computer Communications Group of the Trans Canada Telephone System.

dataphone – (1) A generic term to describe a family of devices to facilitate data communication. (2) An AT&T designation for a service which provides data communication over telephone facilities.

Dataphone digital service (DDS) – A communications service of the Bell System in which data is transmitted in digital rather than analog form, thus eliminating the need for modems. See acronym list for other uses of DDS.

Data terminal equipment (DTE) – (1) Provides for the communications control function (protocol). (2) Any piece of equipment at which a communications path begins or ends.

Deadlock - Unresolved contention for the use of a resource.

Debug – Checking the logic of a program to isolate and eliminate the mistakes from a computer program or other software. Synonym: troubleshoot.

Decibel (dB) – (1) A unit of measure represented as a ratio of two voltages, currents or powers. (2) Measurement of transmission loss or gain.

Decision table – (1) A matrix of contingency plans with the actions to be taken. [Sometimes used in place of flowcharts for program documentation.]

Dedicated access line (DAL) – A non-switched circuit or path connecting the customer’s telephone equipment to the Sprint switch with no intermediate switching functions by the Local Exchange Company (LEC). [Customers with DALs access the Sprint network directly and can use rotary or DTMF signals.]

Dedicated line – A permanently assigned path to specific data terminals which is not part of a switched network. Synonym: private line.

Delay dial – A switching configuration whereby local equipment will wait until it receives the entire telephone number before seizing a circuit to transmit the call.

Delay distortion – Noise or echo resulting from the non-uniform speeds of various signal components of transmissions through a transmission medium(s).

Demodulation – Conversion of a signal from either digital or analog to its original form. Antonym: modulation.

Denial – Call condition that occurs when no circuits are available and a busy tone is returned to the calling party. [This situation is distinctly different from delay in that denial is not time-related and can only be measured in terms of the percentage of calls denied.] See blocking.

Deregulation – (1) A 1983 Federal Communications Commission ruling which freed Sprint and other interexchange carriers from the need to file rate changes or seek authority from FCC to expand. AT&T was not deregulated because of its economic power and market dominance.

DHCP – Stands for “Dynamic Host Configuration Protocol”. This protocol is based on BOOTP and BOOTP clients can still connect to a DHCP server. DHCP allows for dynamic allocation of network addresses and configurations to newly attached hosts, as well as recovery and reallocation of network addresses through a leasing mechanism. Rather than an administrator visiting each computer on a network and entering configuration data (IP address, default router, network mask, DNS server, NTP [Network Time Protocol] server, etc.), all computers are configured the same – to use DHCP. When the computers boot, they receive all of this configuration information from the DHCP server. If configuration information needs to change it can be edited in one place, the database, and each affected computer will receive the update. (For a DHCP FAQ see http://web.syr.edu/~jmwobus/comfaqs/dhcp.faq.html)

Diagnostic - Means of detection, discovery and further isolation of an equipment malfunction or a processing error.

Dial access – (1) Connection through the public switched telephone network. (2) Means of providing a terminal switched access to a service, network or computer.

Dial exchange – An automated switching junction or central office. For example, a PBX permitting call placement by rotary or pushbutton dialing rather than by an operator.

Dial level – The selection of stations or services associated with a PBX using a one- to four-digit code (for example, dialing nine for access to outside dial tone).

Dial pulse – A short duration, direct-current signal produced by or simulated to emulate the opening and closing of contacts in a rotary telephone dial when dialing numbers. Dial pulses control the action of telephone switching equipment. Also called rotary dialing.

Dial repeating tie line/dial repeating tie trunk – A private line communications arrangement which links two or more points together and permits direct trunk to trunk connections without use of an attendant.

Dial selective signaling – A multipoint network in which the called party is selected by a prearranged dialing code.

Dial tone – An audible signal indicating that automatic switching equipment is ready to receive signals required for a connection.

Dial-up – Use of a rotary or dual tone multi-frequency (DTMF) telephone to initiate a station-to-station telephone call over the public switched network.

Dial-up line – (1) A communications circuit that is established by a switched circuit connection. (2) Any circuit available over the public switched network.

Dialing plan – A description of the telephone number assignments for customer use on a telecommunications network.

Digital multiplex system (DMS) – A means of utilizing technologies that provide digital switched service for voice and data transmission. [DMS is characterized by the use of pulse code modulation (PCM) and time division multiplexing (TDM) throughout the switched network. It allows the direct switching of PCM signals used in transmission systems without their conversion to analog format.]

Digital signal (DS) – (1) A nominally discontinuous electrical signal that changes from one state to another in discreet steps. (2) A signal that is time-wise discontinuous (i.e., discreet) and can assume a limited set of values. Antonym: analog.

Digital signal hierarchy – A series of standardized increments for multiplexing of digital channels in T-carriers an other types of carrier systems for digital transmissions. The North American DS hierarchy is structured differently in other global regions.

Ds0 - Digital Signal level zero. One 64 kbps capacity path, equivalent to one voice (analog) circuit.

Ds1 – Digital Signal level one. One 1.544 Mbps digital signal comprised of 24 voice grade lines, each with 64 Kbps capacity. (See T1)

Ds1c – One 3.152 Mbps pipe, equivalent to 48 voice grade lines, each with 64 Kbps capacity.

Ds1 drop and insert arrangement – DS0-level channels are connected to and terminated at intermediate points between the originating and terminating locations within a network.

Ds1 fan-out arrangement – DS0-level circuits are routed to several different locations from the single DS1 termination.

Ds1 private line – An 1.544 Mbps leased, owned or otherwise dedicated circuit available through the LECs interexchange carrier (POP-to-POP or interLATA) or alternate carriers. Sprint product: CLEARLINE 1.5

Ds2 – Digital signal level two. One 6.312 Mbps channel, equivalent to 96 voice grade lines, each with 64 Kbps capacity.

Ds3 – Digital signal level three. One 44.736 Mbps channel, equivalent to 672 voice grade lines, each with 64 Kbps capacity.

Ds4 - Digital signal level four. One 375.176 Mbps channel, equivalent to 4,032 voice grade lines, each with 64 Kbps capacity. Typically used in interoffice transmissions.

Digital technology – Method of storing, processing and transmitting information through the use of electronic or optical pulses that represent binary digits or bits (0 and 1).

Digital transmission system - A transmission system in which information is transmitted in a series of pulses, and in which the signal can be regenerated. See also pulse modulation and time division multiplexing.

Digitizer – Device used to convert an image to a series of dots that can be read, stored and manipulated by the computer. [A digitizer often scans video input, while a scanner usually scans hard copy input.]

Diode - A two-electrode electron tube or its semiconductor equivalent. [Usually employed as liquid crystal diodes (LCD) or light emitting diodes (LED) and are especially applicable to portable computers.]

Direct call – A facility which avoids the use of address selection signals or typed dialing sequences. The network interprets the off-hook status or call request signal as an instruction to establish a connection with a single destination address previously designated by the user.

Direct distance dialing (DDD) – A toll service that permits customers to place their own long distance calls without the aid of an operator.

Direct inward dialing (DID) – A PBX or CENTREX feature in which incoming calls are completed to extensions without the assistance of an operator.

Direct mail – Any type of advertisement, brochure or printed piece delivered to a targeted audience, usually through the postal service.

Direct outward dialing – A PBX or CENTREX feature that allows a station user to gain access to the public switched network without the assistance of an operator.

Direct response – Refers to direct mail and telemarketing campaigns.

Discrete – Pertains to separate and distinct parts of data such as holes in a card or graphic characters.

Discrete cosine transform – An audio coding algorithm.

Disk – (1) A magnetic recording medium. (2) A magnetically coated platter that stores programs and data files. [The two main types of disks are hard disks and floppy disks.]

Disk operating system (DOS) – The software that provides instructions for system hardware operation and data processing.

Distortion – (1) Any change from the original wave form or signal. (2) Normally, non-predictable changes which interfere with interpretation of the result.

Distributed data processing (DDP) - Use of computer systems or intelligent terminals at multiple sites within an organization to perform data processing and/or storage functions.

Distributed systems – Arrangements wherein an organization’s computer complex has many separate computing facilities interfaced and working in a cooperative manner.

DNS – Stands for “Domain Name System”. This service maps an internet domain name to an IP address and visa versa. ITCom already runs a production DNS service. By integrating this service into this project a synergy can be achieved. Most DHCP/DNS systems require manual configuration of the associated data. This project plans to automate much of this process. A new computer is plugged into the network. The user authenticates and DHCP and DNS servers are automatically configured with the appropriate data. (For general DNS information see http://www.dms.csiro.au/~marka/dns.html)

Down time – Period during which a computer, communications line or other device is not operating correctly because of mechanical or electronic failure. (As opposed to available time, idle time or stand-by time.)

Download – (1) Transferring files from one computer to another. (2) Loading fonts from a computer to a printer.

Downstream – The latter stages of processing in a computer program or system.

Drop – (1) The portion of an outside telephone plant which extends from the telephone distribution cable to the subscriber’s premises. (2) A connection point for a terminal on a line.

Dry circuit – A circuit which transmits voice signals and carries no direct current.

Dual tone multifrequency (DTMF) - Type of signaling which emits two distinct frequencies for each indicated digit. Synonym: push button dialing, touch tone dialing

Dumb terminal – (1) Conversational display terminal with limited resident intelligence. (2) Terminal capable of receiving and transmitting data from a host computer over a communications network.

Duplex – (1) Two units in one. (2) Simultaneous two-way independent transmission. Synonym: full duplex.