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A3

ISO page size 11.9" x 16.5" (303 mm x 420 mm); one of the available NaturalFax page width formats.

A4

ISO page size 8.25" x 11.6" (210 mm x 297 mm); one of the available NaturalFax page width formats.

A B C D bits

The four signaling bits used in channel associated signaling. The value that these bits take determines or indicates the state of the telephone channel. Many protocols do not use all four bits. Usually, only the A and B bits are used in North America, but all four are used in Europe. See also CAS.

A bit

See also A B C D bits.

A-law

An encoding scheme that determines how an analog speech signal is converted to a digital signal. A-law encoding is used in Europe. The other algorithm, mu-law, is used in North America and Japan. See also mu-law.

abortmask

In the CT Access ADI service, a bitmask used with the ADI service play and record functions to indicate which DTMF digits abort an active play or record operation. See also DTMF.

ACU

Automatic Call Unit; an ISDN entity directly above the network layer. When the AG ISDN protocol stack is in ACU stack mode, the application uses the AG ISDN Messaging API to send message sequences to the ACU and handle network responses. When the AG ISDN protocol stack is in NCC stack mode, the TCP instances communicate with the ACU. See also ACU stack mode, ISDN, LAPD stack mode, NCC stack mode, protocol stack.

ACU stack mode

An AG ISDN protocol stack mode in which the protocol stack implements all ISDN layer 2 and layer 3 functionality, but no channelizer is present. Without a channelizer, one application performs call control for all channels; with a channelizer, a separate application instance can perform call control for each channel. The application communicates directly with the ACU using the AG ISDN Messaging API. See also ACU, LAPD stack mode, NCC stack mode.

address

In telephony, the number dialed by a calling party which identifies the party called. Also known as the telephone number.

ADI service

A CT Access service that provides all AG board device-level functionality. Functions are provided for establishing and maintaining network connections, determining call status, playing and recording voice messages, and generating and detecting DTMF and other tones. See also CT Access, service.

ADPCM

Adaptive Differential Pulse Code Modulation; a method for digitizing and compressing speech data.

ADSI

Analog Display Services Interface; a specification for sending display information over ordinary telephone lines. For example, used in caller ID. See also ANI, caller ID.

ADSL

Asymmetric Digital Subscriber Line; a method for moving data over regular phone lines at broadband rates (above 1 Mbyte/s). ADSL permits data to be uploaded and downloaded at different rates of speed, hence, asymmetric. ADSL can be considered as an alternative to ISDN, allowing higher speed data transmissions in cases where the connection is always to a known terminal which can support the specified speed.

AG

Natural MicroSystems' Alliance Generation product line of telephony and voice processing hardware.

AGC

Automatic Gain Control; an algorithm applied to incoming speech before compression and storage so that the amplitude of the stored speech is kept at a target level. See also gain.

AG configuration file

Text file (usually named ag.cfg) that provides configuration information for all AG boards in a system. The AG configuration file also specifies runtime software such as DSP files and TCPs to download to the AG board(s) as part of board initialization. agmon uses the AG configuration file to initialize and load the AG boards in the system. See also agmon, DSP file, TCP.

AG driver

The device driver on the host computer that provides the interface to the AG board(s).

AG ISDN Messaging API

An API supplied with AG ISDN which enables an application to communicate directly with Q.931 (layer 3) call control in the ISDN protocol stack. Switch- and country-invariant D channel messages are exchanged with the application at this interface. See also D channel, ISDN, protocol stack, Q.931.

agmon

Utility program which reads a configuration file and uses it to load and monitor AG hardware.

AIS

Alarm Indication Signal; a signal that replaces the normal traffic signal when a maintenance alarm indication has been activated. An AIS is transmitted downstream indicating that an upstream failure has occurred. See also blue alarm, red alarm, yellow alarm.

Alarm Indication Signal

See AIS.

AMI

Alternate Mark Inversion; the line-coding format in T1 transmission systems where successive ones (marks) are alternately sent with opposite polarity, to reduce cross-talk. See also cross-talk, T1.

analog

Information represented by a continuous and smoothly varying signal amplitude or frequency. See also digital.

ANI

Automatic Number Identification; a network service that provides a called party with the phone number of the calling party. It is typically available to the called party in R1, R2, and ISDN signaling systems. The implementation of ANI can vary between different telephone companies and even different central office switches. See also ADSI, caller ID.

API

Application Programming Interface; a library of function calls that allow an application developer to access functionality in a uniform and consistent way.

ASCII

American Standard Code for Information Interchange; a standard used for numeric representation of alphanumeric characters.

asynchronous

Refers to circuitry and operations without a common timing or clock signal.

asynchronous function

Enables concurrent processing between hardware boards and the host CPU. In telephony, an application initiates functions on a telephony board and continues its own processing as it waits for the results of those functions. See also synchronous function.

Audio Compression Manager (ACM)

An extension of the basic Windows NT multimedia system that decodes or encodes waveform-audio data before passing it to or from a waveform-audio device driver.

autofallback

A feature of MC1 board architecture that allows clock slaves to dynamically change clock source references from the clocks driven by the primary master to the clocks driven by the secondary master. See also clock master, clock slave, MC1 board, primary [clock] master, secondary [clock] master.

Automatic Call Unit

See ACU.

Automatic Gain Control

See AGC.