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A method of coding an analogue signal digitally which is used mainly in Europe and Asia. Similar to mu-law, but uses a different amplitude table mapping, so that recordings made with A-law coding are not compatible with mu-law.

Automatic Call Distributor. A specialised form of PBX used in call centres. Provides call queuing, different agent groups and managerial information. Often has more exchange lines than agent positions.

The Association of Computer Telephone Integration Users and Suppliers

Adaptive Differential Pulse Code Modulation. A method of digitally compressing PCM voice data where each digital value (sample) represents an increase or decrease from the previous sample, rather than an absolute amplitude value.

Analogue Display Services Interface. A standard for the transmission of text information over a telephone line, to display text information on devices such as screen phones and to accept DTMF responses from the user.

Analogue Expansion Bus. An analogue voice processing bus used to connect additional analogue devices to a standard Dialogic voice processing card. Used, for example, to connect voice recognition or fax resources.

A member of a call centre who receives inbound or makes outbound calls.

(As in analogue phone line or analogue transmission) - where an electric signal carrying information is represented by a continuously variable voltage or amplitude - i.e. not digital.

USA term for CLI.

Application Programming Interface.

Automatic Speech Recognition - see also voice recognition.

A term originally used to mean the provision of spoken information over the telephone (from 'audio text'), but now more commonly used to refer to the provision of passive or interactive voice services over premium rate telephone lines. For example weather forecasts, horoscopes.

Auto Attendant
An automated voice processing and call processing system which allows callers to automatically route themselves to a person or department within a company


The 64K bit per second voice or data stream on a Basic Rate ISDN line - which can also be at 56K bits per second in the USA. The 'B' comes from 'bearer'.

Basic Rate Interface. A term used to describe an ISDN connection usually comprising two 64K bit per second voice or data streams and one 16K bit per second signalling / data channel. Often referred to in the UK as ISDN2.

Term used to describe the line condition when the called party's telephone is already in use. Usually known in the UK as 'engaged'.


Call Processing
A system which routes calls, usually as the result of a caller's interaction with a Voice Processing System.

A service which allows calling line identity information to be displayed on a special phone or display.

Calling Line Identity
See CLI.

1) Channel Associated Signalling.
2) Communicating Applications Standard - a joint Intel / DCA API for controlling fax modems. CAS allows an application to submit files to a queue for faxing when the modem is available.

Calling Line Identity - information received from the telephone exchange giving the calling party's telephone number. Sometimes referred to as CLID.

Central Office - the 'public' telephone switches used by the telecomms companies to route calls. Known in the UK as 'telephone exchange'

Customer Premises Equipment.

Called Subscriber Identifier - the name or number sent by a fax machine to identify its origin.

Computer Telephony Integration - the linking of computer systems to telephone switches to provide advanced features such as power dialling, the automatic routing of incoming calls to an appropriate employee, or to automatically display caller's account details on an agent's terminal before the call is answered. CTI can exist with or without voice processing and is often misused in the author's opinion to describe 'stand-alone' voice mail or IVR systems which do not establish any data communications with the PBX. Also known as CST (Computer Supported Telephony), CIT (Computer Integrated Telephony) and CAT (Computer Aided Telephony).


The 16K bit per second data / signalling stream on a Basic Rate ISDN line. The 'D' comes from 'data'.

Digital Access Signalling System no. 2. An ISDN signalling system used in the UK.

Dynamic Data Exchange - a communications protocol for transferring data from one computer program to another, either on the same machine or over a LAN.

Direct Dialling Inward - The presentation of the last 2, 3 or 4 digits of a dialled telephone number to a PBX to switch the call to the relevant employee. Commonly used for CTI, Audiotex and IVR systems to activate different services depending on the number dialled, even though the call is delivered over the same physical telephone line. Known in the US as DID.

Dial Pulse
A term used to describe a telephone which dials numbers through a series of 'make' and 'break' connections to the loop current. i.e. an older non-tone phone.

The largest manufacturer of voice processing hardware.

Direct Inward Dialling (See DDI).

(As in digital phone line or digital transmission) - where the signal carrying the (voice) information is represented by a set of finite numerical samples - i.e. not analogue. See also PCM.

Dynamic Link Library. Sharable software libraries, used by Microsoft Windows, which are loaded as they are required at run-time.

Dialled Number Identification Service - Similar to DDI but returning the whole dialled number rather than the last few digits.

Digital Private Network Signalling System - A UK specific digital signalling system used (mostly) to link PBX's together.

Drop and Insert
Describes a voice / call processing configuration where the voice processing hardware sits 'in-line' so that some action can be taken on the incoming call before 'inserting' it into the outgoing trunk.

Dual Tone Multi Frequency - the technical term for the tones generated by a touch-tone telephone. So called because each button on the telephone is represented by two simultaneous tones, one of a high frequency and one of a low frequency. There are four different high tones and four low tones giving 16 unique combinations in total. Usually only 12 of these are used (0 to 9, * and #), but 4 additional codes, named A, B, C and D, are also available.


A digital signalling protocol used in Europe and Asia. E-1 operates at 2.048 M bits per second and provides thirty 64K bits per second data channels and two 64 K bits per second signalling channels. Similar to T-1 used in the USA.

Earth Recall
A method of signalling a recall to a PBX used in the UK. An alternative to time-break recall or flash hook.

European Computer Manufacturers' Association.

European Telecom Standards Institute.

A relatively new signalling system to provide a Europe-wide standard for ISDN.


Fax back
See Fax on demand.

Fax on demand
A automated system whereby a caller can request a document (or documents) to be faxed to them through the use of voice processing. Can be either during the same call, whereby the caller must call the system from a fax machine and press the 'start' button at the appropriate time (so the caller pays for the phone call) - or the system can dial out to a fax machine specified by the caller. Also known as fax-back.

Fax Processing
A generic term to describe the act of receiving, storing, manipulating and transmitting fax information to or from a computer equipped with fax modem hardware.

First Party CTI
A method of implementing CTI where the computer views the PBX from an individual's telephone point of view. i.e. it can receive information regarding incoming and outgoing calls on one line, but is unaware of the state of other calls on the PBX. TAPI allows implementation of first party CTI. See also Third Party CTI.

A common method of signalling a recall to a PBX. Consists of breaking the loop current for about 500ms and reconnecting it.

See Fax On Demand.


The condition when a voice processing system goes off-hook to place an outbound call, but inadvertently connects to an incoming call which arrived momentarily beforehand - i.e. before ringing was detected.

Graphical User Interface

Grunt detection
A simple method of allowing callers to navigate though a menu without using DTMF recognition or speech recognition. Grunt detection is simply the detection of a noise or silence to implement a two-way choice through a interactive voice dialogue. For example "If you would like the sales department say YES - otherwise remain silent".


Hidden Markov Model - a mathematical technique commonly used to implement speech recognition algorithms.


The governing body in the UK controlling the use of premium rate telephone information services.

(As in inband signalling) Used to describe the transmission of additional data concerning a telephone call (such as the called party identity), within the signalling bandwidth of the voice channel. An example of inband signalling is where a PBX sends information as DTMF tones.

Information Provider
The person or company providing content which is made available over the telephone network through a service provider, usually on premium rate lines.

Industry Standard Architecture. The standard 16 bit bus architecture used in PCs.

Integrated Services Digital Network - An international standard for voice and data communications where the transmission medium is digital from caller to called party.

UK term to mean Basic Rate ISDN. The '2' comes from the number of digital channels available.

UK term to mean Primary Rate ISDN. The '30' represents the maximum number of digital channels available on an E1 / ISDN line.

International Telecommunications Union. A International body promoting the adoption of telecommunications standards to ensure compatibility of telecommunications facilities between countries. Formerly known as CCITT.

Interactive Voice Response system - a system which allows a caller to access computer based information and possible to change that data or initiate requests. The most widely known IVR application is telephone banking.


An electrical 'loop' is made when an analogue telephone's handset is lifted. This allows 'loop' current to flow from the telephone exchange.

Local Area Network. Used to link computers together, within an office or building.


Multi-frequency - a signalling system used to communicate between telephone exchanges and across digital lines to certain customer premises equipment (such as R2 digital systems). Note this is not the same as DTMF or touch tone.

Alternative name for DTMF or touch-tone sometimes used in the UK.

Also known as u-law. A method of coding an analogue signal digitally which is used mainly in the USA. Similar to A-law, but uses a different amplitude table mapping, so that recordings made with A-law coding are not compatible with mu-law.

Multi Vendor Integration Protocol. A digital bus used to carry voice and fax information between voice and fax processing components from different suppliers within a PC. Supports up to 256 individual voice channels.

IBM developed chip-set to provide voice / fax / data modem for use under Microsoft Windows.

Message waiting indication. A feature supported by some PBX's that allows a voice processing system to 'set' a light or some other indicator on an individual's telephone to show that a message has been stored for them.


A 32 bit version of VBX custom controls. OCXs are based on Microsoft's published OLE specification and also know as OLE controls.

Open DataBase Connectivity. A widely supported standard to provide a common programming interface to databases from different suppliers.

The state a telephone is in when its handset is lifted.

Object Linking and Embedding. An open architecture from Microsoft to promote object oriented applications and programming tools across the Windows family of operating systems.

The state a telephone is in when is handset is not lifted.


Private Automatic Branch Exchange - now more commonly referred to as just PBX (see below).

Private Branch Exchange - the telephone switching system used within individual companies.

Personal Computer - A computer which conforms to the hardware and software model developed by IBM in the 1980's, and is now widely used as an open platform for developing voice and fax processing systems.

Pulse Code Modulation - a method of representing an analogue signal digitally. This is achieved by sampling the amplitude of the analogue signal at regular intervals and representing each sample by a digital value. The maximum frequency which can be represented in this manner is half the frequency of the sampling frequency.

PCM Expansion Bus - A digital bus used to carry voice and fax information between voice and fax processing components from different suppliers within a PC. Supports up to 32 individual voice channels.

Plain Old Telephone Service - used to refer to basic analogue telephone connections with no advanced features.

Power Dialler
An automated system which makes outbound calls for a call centre agent - see also predictive dialler and preview dialler.

Predictive Dialler
An automatic system which places outbound calls and uses statistical modelling to start dialling the next call before an agent is free to handle it, on the grounds that by the time the call has been answered an agent should be available.

Premium Rate
Describes a range of telephony tariffs where the 'service provider' receives a percentage of the call cost, paid by the telecomms company. Frequently used to offer information and entertainment services over the telephone network.

Preview Dialler
An automated system which shows the details of the next person to be called on an agent's screen. The agent can then allow the preview dialler to automatically place the call, or can skip these details and view the next contact's details.

Primary Rate Interface. A term used to describe an ISDN connection based on E-1 or T-1 trunks. Provides 30, 64K bits per second voice or data streams on E-1 (European) circuits or 23 64K bits per second voice or data streams on T-1 (USA) circuits. Often referred to in the UK as ISDN30.

A pre-defined sequence of signals used to control flow of information between two systems - frequently between a telephone exchange and some customer premises equipment, or between two computer systems.

The Public Switched Telephone Network.

The signals generated from an older style, non tone, telephone.

Pulse Recognition
A system which can understand the click sounds generated by a pulse phone so that users of such phones can control voice mail and IVR systems. Like speech recognition, pulse recognition is not 100% accurate, so care is needed when designing systems using such techniques.

Pulse to tone converter
A system which performs pulse recognition and then generates the corresponding DTMF tone. Used to give IVR and voice mail systems with tone recognition the ability to respond to callers with pulse phones.


An ISDN signalling system - as used with EuroISDN.

The ability of an ACD or voice processing system to form a 'queue' of incoming callers destined for an agent or agent group.


Signalling system commonly used on E1 lines in Europe and Asia. Note however that there are several flavours of the R2 protocol

A 'request' sent to a PBX to put the call on hold and accept further commands. Most commonly used to transfer a call from one extension to another. Can be either an earth recall, flash-hook, or timed break recall.

Standard US telephone connector.

Telephone connector similar to RJ11, but which handles two telephone devices.

Robbed-bit signalling
A method used on T-1 lines to carry signalling information. As there is no spare bandwidth to carry signalling information as well as voice data, every 6th sample of voice data contains just 7 bits of voice data and 1 bit of signalling information.

Rotary (Dial)
Alternative term to describe a pulse dialling phone.

Ring Tone No Reply - what happens when the number you dial doesn't answer.


Speech API. An upcoming Microsoft API for implementing speech recognition on the desktop or over the telephone. To be supported by most major speech recognition companies.

Signal Computing bus - A replacement for the PEB bus. SCbus supports up to 2048 simultaneous voice / data channels. It can also operate in PEB and MVIP modes for backward compatibility.

Signal Computing System Architecture - A scaleable open architecture for connecting voice, fax, and video devices together, initiated by Dialogic. SCSA encompasses both hardware (the SCbus) and software API's.

Service Provider
The individual or company operating the voice or fax processing equipment connected to premium rate lines. The service provider receives a percentage of the telephone call cost from the telecomms company and in turn pays the information provider their fee. Of course, the service provider and the information provider can be the same person or company.

Special Information Tone - a series of tones generated by telecomms companies prior to issuing a voiced announcement. Used to enable automated equipment to interpret the announcement.

Used to mean all the channels in one T-1 or E-1 digital connection. Also referred to as a trunk.

Speech Recognition
See Voice Recognition.

Speaker Identification
The identification of a person from their voice samples, without having any prior information as to who they are. This is an extremely difficult task used only (to the author's knowledge) in forensic science - not in day to day computer telephony applications. It is an often misused term, however, instead of Speaker Verification (see below).

Speaker Verification
A technique used to provide additional security to voice processing systems, where the voice sample of the caller is compared with a pre-registered sample of the valid user so that the caller may be accepted as the valid user or rejected as an impostor. This technique requires the caller to announce who they claim to be first (through the use of an ID number for instance). Used in some telephone banking systems.

Structured Query Language - a standard method of accessing database information though an 'English-like' expression which follows a strict format.

Signalling System Number 7 - also known as CCITT No. 7 - A digital signalling protocol most frequently used for communication between telephone exchanges.

A telephone device.

General term to mean an ACD, PBX or telephone exchange.


The US equivalent of E-1. T-1 lines operate at 1.544 M bits per second and carry a maximum of 24 voice calls. Similar to E-1, but as there are is no spare bandwidth to carry signalling information robbed-bit signalling is used.

Telephony Application Programming Interface. A Microsoft / Intel initiative to provide a common interface for developing telephony applications from the desktop. TAPI allows developers of call and voice processing systems to write code which is hardware independent - allowing applications to work equally well with a TAPI compliant voice / fax modem, voice processing card or PBX driver software. TAPI allows implementation of 1st party CTI.

Transmission Control Protocol / Internet Protocol. A data protocol for transmitting information between computer systems (usually UNIX based) and across the Internet.

The synthetic generation of voice constructed from pure text input. Text to Speech techniques are used where an IVR system has to speak out information which cannot be pre-recorded (such as speaking out e-mails) or where the data to be spoken would be impractical to have pre-recorded (such as rapidly changing product names, or vast customer databases). The quality of text to speech synthesis is improving, but should only be used when pre-recorded speech cannot, due to its robotic sound and poorer intelligibility than pre-recorded speech.

Third Party CTI
A method of implementing CTI where the computer views the PBX as if it were the operator. i.e. it is aware of the state of all calls on the PBX. TSAPI allows implementation of third party CTI. See also First Party CTI.

Tagged Image File Format. - a standard method of digitally encoding picture information. TIFF Class F (TIFF/F) is commonly used in fax processing systems.

Timed Break Recall
A common method of signalling a recall to a PBX in the UK. Similar to a flash-hook, but typically of a shorter duration (often around 150ms).

Touch tone
A non technical term used to describe DTMF.

Used to mean a T-1 or E-1 digital connection. Also referred to as a pipe or span.

Telephony Server Application Programming Interface. A Novell / AT&T initiative to provide a common interface for developing telephony applications. Unlike TAPI, TSAPI allows implementation of 3rd party CTI.

See Text-to-Speech


Also known as mu-law. A method of coding an analogue signal digitally used mainly in the USA. Similar to A-law, but uses a different amplitude table mapping, so that recordings made with a-law coding are not compatible with u-law.

Unified Messaging
The integration of e-mail, voice mail and fax mail at the desktop.


Also known as Custom Controls. Introduced by Microsoft in their Visual Basic programming language, VBXs are a method of extending the functionality of languages or applications by adding in new objects.

Voice Mail
A system which provides a 'corporate-wide' answering service and which allows users to retrieve messages from within the office and remotely.

Voice Recognition
Software and (usually) hardware which analyses the caller's speech samples to determine which word out of a finite set of words has been spoken. Used as an alternative method for callers without tone phones to input data into IVR systems or to control voice mail systems. Voice recognition can be 'isolated' where each word has to be spoken individually, or 'connected' whereby words can be spoken without gaps between each word. Additionally, voice recognition systems can be 'speaker dependent' if they require prior training to recognise an individual's voice or 'speaker independent' if they recognise a word spoken by many different people, with different accents, without prior training.

Voice Response Unit.

(As in VOX file) - A type of computer file used to store a voice file digitally - commonly used by Dialogic voice processing hardware.


(As in WAV file) - A type of computer file used to store a voice file digitally - commonly used by Microsoft Window's applications.

A device which is connected to an ACD or call processing system and which displays information to call centre agents about the current state of the call centre's queue - such as the number of callers waiting or the longest waiting time.

A telephony function provided by voice processing hardware to request calling line identity information from the telephone exchange. Wink is used in the USA, but not in the UK.


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