Index - 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 A-Z
D CONDITIONING - A type of channel conditioning setting limits on harmonic distortion and signal-to-noise ratio of analog signals. Largely archaic in that it was developed as a result of flaws in the design of T carrier channel banks long since removed from the plant.
DATA - Multiple units of information. Singular is " datum ".
DATA ACCESS ARRANGEMENT (DAA) - Once a mandated form of Network Protective Device ( NPD ) for COAM data devices, some still require a DAA for physical interfacing.
DATA CIRCUIT - Communications channels provided specifically for the exchange of data as compared to voice or other information forms. Modern data terminals often operate effectively on channels not so designated, offering users economy and flexibility of operation.
DATA COMMUNICATIONS EQUIPMENT (DCE) - Standards body term for devices that perform signal conversion at the extremities of a data circuit. A data set ( modem ) or a CSU are common examples of a DCE. Compare to DTE.
DATA ENCRYPTION STANDARD (DES) - A cryptographic standard defined by the former National Bureau of Standards ( NBS ), now the National Institute of Science and Technology ( NIST ) for the general public to encrypt and decrypt digital and data transmissions.
DATA LINE INTERFACE - PBX term for a point at which a data station can be connected to wiring.
DATA LINE PRIVACY - A line exclusion function provided on data and fax lines to prevent noises from other users picking up the line during facsimile or data transmission use.
DATA LINK - A serial data communications pathway, generally between two adjacent nodes without an intervening node.
DATA LINK CONTROL - 1.) Synonomous with link layer data protocols 2.) The second layer of the ISO Reference Model for Open Systems Interconnection ( OSI ).
DATA OVER VOICE (DOV) - Frequency Division Multiplexing of local physical wire within a premises to provide simultaneous and independent data transmission capability on twisted pair telephone wiring; capable of providing a fairly efficient form of LAN, largely for lower-speed async terminals; the basis of AT&T's Datakit product sold by LECs under various names largely to Centrex customers.
DATA PBX - A specialized switching unit operating on
switching DCE - DTE interfaces, most typically RS-232 type.
DATA SERVICE UNIT (DSU) - DTE interface unit used in combination with a CSU to connect data terminals to transmission facilities. Contains interface control circuitry not located in the CSU. (Note that some CSU's also contain DSU functions.)
DATA SET - A device converting data into signals suitable for transmission over telecommunications lines; the term "modem" commonly used by computer communications personnel has a much broader sense and range of application in general telecommunications.
DATA TERMINAL - A station in a system capable of sending and/or receiving data signals.
DATA TERMINAL EQUIPMENT - The standards-body term for a computer, user terminal, workstation or personal computer used for data communications; abbreviated DTE . Compare to DCE .
DATA UNDER VOICE (DUV) - AT&T's earliest means of intercity and interstate transmission of DDS by Frequency Division Multiplexing a 1.544 megabit four-phase modem in otherwise unoccupied spectrum space of its analog microwave radios, below the voice channels.
DATABASE - An organized compilation of computerized data. Formalized rules ( CODASYL ) and standardized terminology have the objective of avoiding duplication, controlling access and maintaining currency of contents.
DATAPHONE - Registered trademark of AT&T for both data transmission services and terminals using public networks and channel facilities.
DATAPHONE DIGITAL SERVICE (DDS) - AT&T's registered trademark name for a series of digital transmission services at transmission rates ranging from 2400 bps to 1.544 megabits. Being supplanted in the AT&T product line by products named Accunet.
dBm - Identifier meaning "decibels referred to one milliwatt," the common reference point for power levels in telecommunications circuits.
dBm0 - Identifier meaning "decibels referred to one milliwatt and corrected to a Zero dBm effective power level;" used to state the relation of a signal level on a transmission line at other than a one-milliwatt point. Example: Throughout an analog system, a data set signal is to be kept 13 dB below that for a single test tone, stated as "minus 13 dBm0;" at a carrier modulator input where test tone level is -16 dBm, a data signal should then be 13 dB lower, or -19 dBm.
dBmp - Identifier meaning "decibels below reference ton using psophometric (filter) weighting," the CCITT method for noise measurements; has about 2 dB variance from Bell methods.
dBm0p - Identifier for CCITT psophometric-weighted noise measurements adjusted to a relative 0 dBm transmission level point. Example: An absolute measurement of minus 40 dBmp noise at a carrier channel output point would mean a signal-to-noise ratio of about 47 dBm0p exists at that point on the circuit.
dBrn - Identifier meaning "decibels above reference noise," the reference commonly used being 90 decibels below one milliwatt in North American telecommunications work.
dBrnC - Identifier meaning "decibels above reference noise measured through a (filter) weighting network approximating a " type C voice message channel;" the common North American nomenclature for a DDD trunk channel; having a reference of 90 decibels below one milliwatt of power.
dBrnC0 - Commonly pronounced "de-brink-o," identifier meaning "decibels above reference noise with C message weighting adjusted for equivalence to a 0 dBm (one milliwatt) equivalent circuit point." Example: A direct measurement of 49 dBrnC0 at the nominal +7 dBm output of a carrier demodulator would mean the noise had been offset by 7 dB; thus the reading in DBrnC0 would be 42.
DECIBEL (dB) - A unit of measurement representing the logarithmic a ratio of two voltages, currents or power levels; used in telecommunications to express transmission loss or gain; defined as one-tenth of a Bel, hence the appropriate notation is dB, shown here.
DEDICATED ACCESS LINE (DAL) - An analog special access line going from a user's premises directly to an IEC's POP, bypassing the LEC's switching machine. When the circuit is provided by a local telephone company, they claim it is a "service bypass". When the physical circuit totally avoids the LEC's transmission plant (as with microwave radio or non-LEC fiber paths), the LEC claims a "facility bypass" has occurred.
DEFAULT - 1.) In data systems, the process or action programmed to occur if the user specifies no option; 2.) Regarding Equal Access, the IEC assigned to a line's "1+" dialing sequence; the IEC all calls will be directed to unless the user dials "10XXX."
DEFENSE COMMUNICATIONS AGENCY (DCA) - The U.S. Military's interservices telecommunications operating agency, procuring and operating much domestic military communications and virtually all overseas military communications; based in the Pentagon.
DEFENSE ELECTRONICS COMMUNICATIONS CONTRACTING OFFICE (DECCO) - The U.S.Military's interservices domestic telecommunications services procurement function; located at Scott AFB, IL.
DELAY - In communications technology, the waiting time between two events, such as the time from taking a handset off hook to receiving a dial tone ( Dial Tone Delay ) or the time from completing dialing until the start of ringing at the distant end ( Connection Delay ). Specific to data communications, the time from transmission of communications until a reaction is received. Compare with Propagation Delay, Response Time and Processing Delay.
DELAY DIAL - A mode of operation whereby dial equipment waits until it receives the entire desired number before seizing a circuit to initiate a connection.
DELAY DISTORTION - An unequal propagation delay for tones of different frequencies in passage through a transmission channel. Synonyms: Envelope Delay Distortion ( EDD ); Group Delay .
DELTA MODULATION (DM) - A variant of pulse code modulation whereby a code representing the difference between the amplitude of a sample and the amplitude of the previous one is sent. Uses simpler electronics than PCM (which see elsewhere),but offers limited speech quality for the size channel it uses; limited primarily to military tactical applications and useful for only the simplest, slowest data transmission.
DEMODULATION - The process of retrieving an original inputted waveform from a modulated signal; widely used in numerous ways by telephone carrier systems, data sets and radio receivers of all types.
DERIVED FACILITY/DERIVED FACILITIES - Transmission paths created by use of multiplexing methods that provide more than one virtual path per physical facility.
DESTINATION FIELD - Location in a message header that contains the address of the station for which the message is destined.
DIAL LEVEL - The selection of stations or services associated with a PBX using a one to four digit code (e.g., dialing 9 for access to outside dial tone); alludes to the upward motion of mechanical switches in a PBX.
DIAL PULSING (DP) - The transmitting of telephone address signals by momentarily opening a DC circuit a number of times corresponding to the digit which is dialed; often called " Rotary Dialing ." Compare with " Key Pulsing ".
DIAL REPEATING TIE LINE/DIAL REPEATING TIE TRUNK (DRTL/DRTT) - A tie line arrangement permitting direct trunk to trunk connections without an attendant's intervention; capable of repeating dial pulses to connect trunks in tandem.
DIAL SELECTIVE SIGNALING (SS-1) - A multipoint network in which the called party is selected by a prearranged dialing code; typified by the Bell SS-1 Selective Signaling System.
DIAL TONE - A uniquely identifiable tone showing that automatic switching equipment is ready to receive dial selection signals; International equivalent: "Proceed to Select" signals in various form of telecommunications networks.
DIAL UP - Using facilities of the PSTN to establish a connection.
DIALING PLAN - A description of the dialing arrangements for customer use on a network; DDD is the Bell-generated plan for North America.
DIGITAL CROSS CONNECT (DSX) - A mechanical arrangement of patch jacks and cords or a digital electronic unit that semi-permanently routes digital telecommunications bit streams between its ports to establish commmunications transmission paths. DIGITAL DATA COMMUNICATIONS MESSAGE PROTOCOL (DDCMP) - Digital Equipment Corporation's ( DEC ) synchronous data transfer protocol.
DIGITAL LOOPBACK (DLB) - Testing method in which received data is fed back to the transmitting source without processing; used to isolate circuit problems.
DIGITAL NETWORK ARCHITECTURE (DNA) - The data network architecture of Digital Equipment Corporation ( DEC ).
DIGITAL SIGNALING - Using techniques that transmit information as a series of discontinuous pulsed signals in a pattern representative of the inputted signals; requiring reconstitution at the receiver; capable of being regenerated to minimize noise contribution in transmission. Compare to Analog.
DIGITAL SWITCHING - Establishing and maintaining a connection under stored program control, when information passed through the switching matrix is in the form of binary encoded information. The transmission medium through the matrix is assigned "time slots" on a digital bus. Analog circuits may be switched digitally by providing codecs in the physical ports of the switch.
DIRECT DISTANCE DIALING (DDD) - The Bell-generated plan and service for public calls in North America; permits users to dial their own long distance calls without operator intervention. International equivalent: "Subscriber Trunk Dialing - STD ."
DIRECT INWARD DIALING (DID) - A PBX or CENTREX feature providing for users outside the system to dial directly to a station within the system; often delineated by the last four digits of an exchange number assigned to a specific desktop.
DIRECT INWARD LINE (DIL) - A PBX feature set to dial within the PBX when a designated outside line rings. Similar to a "night connection" of an outside line to a designated station for after hours answering, except electronically reprogrammable.
DIRECT INWARD SWITCH ACCESS (DISA) - A PBX feature that permits outside callers to obtain a PBX dial tone and dial within the PBX If so programmed, outside callers can dial into the DISA, then dial back out again, even on WATS lines; a common source of telephone budget abuse.
DIRECT OUTWARD DIALING - A PBX or CENTREX feature that allows a station user to obtain direct access to an exchange network.
DISTORTION - Generally an unwanted, often unpredicted change in a transmission signal that renders the resulting output less than optimum.
DISTRIBUTED COMMUNICATIONS ARCHITECTURE (DCA) - Data network architecture established in Sperry Univac ( UNISYS ) computer networks.
DISTRIBUTED DATA PROCESSING (DDP) - Using multiple data processing machines or intelligent terminals at locations geographically separated with a shared peer relation rather than a hierarchical relation as has been classic in mainframe data networks; adds a dimension of data communications issues to a network in which all locations are now of equal need to the network's operation.
DISTRIBUTED SYSTEMS ARCHITECTURE (DSA) - The data network architecture of Honeywell Corporation.
DISTRIBUTED SYSTEMS NETWORKING (DSN) - The data network architecure of Hewlett-Packard Corporation.
DIVESTITURE - That portion of the antitrust settlement with AT&T that removed the 22 Bell LEC's from AT&T ownership to public ownership on January 1, 1984.
DROP - The portion of outside telephone plant which extends from the telephone distribution cable to the subscriber's premises.
DRY CIRCUIT - A circuit which transmits voice signals and carries no direct current.
DIGITAL CROSS-CONNECT 1 (DSX-1) - Office twisted pair facilities for interconnecting 1.544 megabit digital streams.
DIGITAL CROSS-CONNECT 2 (DSX-2) - Office coaxial cable facilities for interconnecting 6.312 megabit digital streams.
DIGITAL CROSS-CONNECT 3 (DSX-3) - Office fiber optic facilities for interconnecting 44.736 megabit digital streams.
DIGITAL STREAM 1 (DS-1) - A digital transmission rate of 1.544 megabits in North America; 2.048 megabits in much of the rest of the world; often miscalled "T-1," when it is simply the transmission rate of the LEC's T-1 digital carrier system.
DIGITAL STREAM 1C (DS-1C) - A digital transmission rate of 3.152 megabits per second in North America, containing 2 DS-1's.
DIGITAL STREAM 2 (DS-2) - A digital transmission rate of 6.312 megabits in North America, containing 4 DS-1's. Frequently miscalled "T-2," even though there is no such digital carrier system; it is merely a digital transmission rate.
DIGITAL STREAM 3 (DS-3) - A digital transmission rate of 44.736 megabits, containing 28 DS-1's or one network video signal. Frequently miscalled "T-3," even though there is no such digital carrier system. Carried locally on AT&T fiber optic transmission systems called FT3 or short-haul microwave radio.
DIGITAL STREAM 4 (DS-4) - A digital transmission rate of 274.016 megabits, containing 672 DS-1's. Carried via digital microwave radio (typical of AT&T DR-18) or multiplexed with other DS-4's for carriage via 565 megabit (or even larger) fiber optic lines interstate.
DUAL TONE MULTI-FREQUENCY (DTMF) - Also known as Touch- Tone. A type of signaling which emits two distinct frequencies for each indicated digit. Also called " Key Pulsing " at operator positions in toll networks.
DUMB TERMINAL - A data communications euphemism indicating a DTE with no processing capability. The data equivalent of a KSR teleprinter.
DUPLEX (DX) - Two-way transmission. DUPLEX SIGNALING (DX SIGNALING; DX-1; DX-2)- A long-range bidirectional signaling method for local cable facilities using paths derived from transmission cable pairs. It is based on a balanced and symmetrical circuit that is identical at both ends. This circuit presents an E & M lead interface to connecting circuits at each end.