- D -

D4 framing

A framing format in the T1 environment. The D4 framing bit is used to identify both the channel and the signaling frame. In D4 framing, signaling for voice channels is carried in-band along with the encoded voice. A pattern derived from the framing bit of each individual frame is used to maintain synchronization. See also robbed-bit signaling.

D bit

See A B C D bits.

D channel

The timeslot on an E1 trunk, a T1 trunk, or telephony bus in which common channel signaling information is passed. See also B channel, BRI, CAS, Common Channel Signaling (CCS), ISDN.

data link layer

In the OSI layering model, the data link layer (layer 2) is above the physical layer. Protocols for this layer describe methods for error-free communication between devices across the physical link. One protocol used in this ISDN layer is CCITT recommendation Q.921, also known as Link Access Procedures on the D Channel (LAPD). See also ISDN, Link Access Procedures on the D Channel (LAPD), Open System Interconnect (OSI).

data set

Telephone company term for modem.

datagram

A generic term for a data packet.

DCE

Data Communications Equipment. See also RS-232C.

DCN

DisCoNnect frame; a disconnect message sent by the calling fax terminal to the remote fax terminal before the calling fax terminal releases the call. The calling fax terminal can release the call as soon as it sends the DCN frame; it does not need to wait for a response from the remote terminal. See also Group 3 fax, T.30.

DCS

Digital Command Signal; the setup command used by a calling fax terminal in response to Digital Identification Signal (DIS). The DCS determines the attributes of the fax transmission to follow (transmission speed, resolution, etc.). See also DIS, Group 3 fax, T.30.

decoding

A decompression technique used for changing a digital signal into an analog signal or into another type of digital signal.

default channel

In AG ISDN, the B channel bound to the same CTA context as the AG ISDN TCP instance. The AG ISDN TCP will always request use of this channel when attempting to place an outbound call. In Non-Exclusive Mode, the ISDN TCP instance will accept any B channel that the network assigns. In Exclusive Mode, the TCP aborts the call. See also CTA context, Exclusive Mode, Non-Exclusive Mode, TCP.

device driver

Software which translates the application commands into the code required by the device.

device service

A CT Access service that communicates directly with the hardware providing the functionality.

DID

Direct Inward Dialing; an incoming telephone service which delivers the final portion of the called address to the CPE, thus allowing the caller to reach an individual extension of a PBX. See also CPE, PBX or PABX.

DID number

Direct Inward Dial number; the called number which is collected by the trunk control program and is passed to the application.

digital

Information in a discrete or quantized form. See also analog.

Digital Signal Processor

See DSP.

DIS

Digital Identification Signal; used by the called fax terminal to communicate its capabilities to the calling fax terminal. See also DCS, Group 3 fax, T.30.

discrete word speech recognition

Speech recognition that requires the speaker to explicitly pause between utterances.

dispatcher

In CT Access, the dispatcher handles the routing of commands and events between CT Access services, and between the services and the application. The dispatcher contains built-in services for service setup, command processing, event and error handling, parameter management, and tracing.

dispatcher services

Services addressing common system-level programming needs.

DLL

Dynamic Link Library; a library of software object modules that can be loaded and accessed on demand.

DNIS

Dialed Number Identification Service; a telephone company service that reports the number that the caller was trying to reach. to the called party. For example, a company with multiple 800 numbers would use this service to determine how to respond to an incoming call.

DoC

Department of Communications; the Canadian government agency that regulates communications and the use of the electromagnetic spectrum.

document

In NaturalFax, the image entity to be transferred. It is contained in a single file, and can contain more than one page. Documents to be transmitted by NaturalFax must be in TIFF-F format. Documents received by NaturalFax are stored in TIFF-F format. See also TIFF-F.

document queue

A NaturalFax data structure that contains references to documents. A document queue must be either a send queue or a receive queue. Only send queues can be sent, and only receive queues can be used to receive documents.

DONE event

An event which signifies the completion of an asynchronous function. See also completion event.

DRAM

Dynamic Random Access Memory chip; RAM memory that requires data to be refreshed periodically to prevent its loss in memory. See also SRAM.

drop and insert

The ability to extract data from a timeslot in a PCM stream and replace it with other data. See also PCM.

DSi0..7, DSo0..7

The names of the physical bus wires in the MVIP-90 bus cable that carry the individual unidirectional bit streams. By convention, they are paired up (DSiX, DSoX) to form eight full-duplex MVIP streams. DSi0..7 are designated for input to resource boards and DSo0..7 are designated for output from resource boards.

DSP

In telephony, a Digital Signal Processor; a microprocessor that is designed to perform the calculations required for voice processing.

DSP file

A low-level program, downloaded to an AG board at initialization, that enables an AG board's DSPs to perform tasks such as DTMF signaling, voice recording, and playback.

DSP program file

A software module that programs an AG board's DSPs to perform certain functions. The DSP program files for an AG board to use are specified in the AG configuration file, and are loaded to on-board memory by agmon.

DSX-1

Digital Signal Cross-Connect [X] Level 1; A standard set of parameters for cross-connecting DS-1 lines.

DTC

Digital Transmit Command; used by the calling fax terminal to poll the called fax terminal. See also polling.

DTE

Data Terminal Equipment. See also RS-232C.

DTMF

Dual-Tone-Multi-Frequency; an in-band signaling system that uses two simultaneous voice-band tones for dialing. Also called touchtone.

duplex

See full-duplex, half-duplex, simplex.

Dynamic Random Access Memory

See DRAM.