AL (ATM Adaption Layer). A protocol that translates data into a format that can be interpreted by the ATM Cell.

AAL-1 (ATM Adaptation Layer Type 1). AAL functions that support constant bit rate, time-dependent traffic such as voice and video.

AAL-2(ATM Adaptation Layer Type 2). This AAL is a placeholder for variable bit rate video transmission.

AAL-3/4 (ATM Adaptation Layer Type 3/4). AAL functions that support variable bit rate, delay-tolerant data traffic requiring some sequencing and/or error detection support. Originally two AAL types, that is, connection-oriented and connectionless, which have been combined.

AAL-5 (ATM Adaptation Layer Type 5). AAL functions that support variable bit rate, delay-tolerant connection-oriented data traffic requiring minimal sequencing or error detection support.

AB (Answer Back). A signal from a receiving device that indicates that it is ready to receive data.

Abandoned call. A call that enters the telecommunications network but is terminated by the subscriber before it is answered.

Access fee. The fee paid by cellular subscribers to their carrier for any connections to the local PSTN. The carrier, in turn, pays the local PSTN for the use of their circuits to connect the call.

Access line. The telephone line that connects a call into the switching center (local exchange) of a network.

AC-DC ringing. A technology that uses an alternating current to ring a telephone and a direct current to cease ringing when the telephone is answered.

Acoustic coupler. Equipment used in the conversion of electrical signals into audio signals in order to transmit data over a PSTN.

ACR (Allowed Cell Rate). The rate at which a transmitter is allowed to send signals in ATM systems - measured in cells per second.

ACTS: Advanced Communication Technologies and Services. ACTS was a research program promoted by the European Commission to develop advanced communications technologies.

AD (Abbreviated Dialing). Entering a two-digit or four-digit number into a terminal which has been pre-programmed to recognize the number as an abbreviation for a frequently dialed number which can be automatically dialed by the switching center (local exchange).

Adaptive equalization. The ability of an audio modem to detect variations in signal quality on a telephone line and take steps to compensate for it.

Add-on conference. A system that allows a telephone user to introduce another telephone user into an existing conversation.

Administrative domain. A collection of functional entities in a network that are grouped for administrative purposes.

AFI (Authority and Format Identifier). Included in the header of a transmitted packet. It identifies the format of the incoming message for the receiver.

Aggregate bandwidth. Describes the entire bandwidth of a channel used in a multiplexed bit stream.

Aggregate discount. A discount given to subscribers of multiple optional services based on the aggregate cost of the services.

All number calling. Telephone numbers that contain no letters just numerical digits.

Altair. The name given by Motorola to their wireless local area network.

Alternate routing. A mechanism that supports the use of a new signal path after an attempt to transmit the signal down a previously selected path fails.

AIN (Advanced Intelligent Networks). Networks using sophisticated devices to facilitate roaming by subscribers outside of their home location area.

Airline mileage. The distance in miles between two terminals in a network.

Airtime. The time a subscriber spends on a call.

Algorithm. A procedure or formula used to solve a problem.

Allocation. The designation of a band of frequencies for a specific radio service such as GSM.

Alphanumeric. A message such as SMS that can contain both letters (alpha) and numbers (numeric).

Ambient noise. A noise level that is always present.

AMC (Adaptive Modulation and Coding). A transmitter dynamically employs different modulation and code-rate combinations, to provide different data rates in response to changing channel conditions.

Amplifier. A device that strengthens the signal of an analog transmission. As an analog signal moves further from its point of origin, it weakens in strength, so amplification is required to restore the signal quality for the receiver.

Amplitude. The distance between the high and low points on a signal or waveform.

AMPS (Advanced Mobile Phone System). The U.S. technical standard for an analog mobile phone system.

Analog. A method that uses variations in frequency to carry signals. Analog means 'analagous' or 'copy of'. Analog technology transmits voice signals in the form of electrical signals whose frequency and amplitude are proportional to the vibrations in the voice. Traditional wireless telephones use analog technology.

Analog cellular. The standard for equipment using cellular telephones using radio wavelengths to transmit telephone calls.

Analog channel. A channel that has no limitations on the amount of data it transmits.

Analog signal. In wirless telecommunications, a continuous signal that reflects variations in loudness of a human voice.

Ancillary charges. Charges for optional services delivered by a carrier.

ANSI (American National Standards Institute). A voluntary standards organization of the USA and is a member of the International Standards Organization (ISO). It is a clearing house for standards, generally adopting standards proposed by smaller companies and organizations within the USA.

ANSI-41. A US core-network standard developed to support roaming between different cellular systems.

ANSI emulation. The ability of a device to send, receive, and display ANSI (American National Standards Institute) graphics.

Antenna. A device that both transmits and receives radio frequencies.

Antiope. The teletext system used in France.

AP (Access Point). A bridge-like device that attaches 802.11 WLAN stations to a wired backbone network.

AOSP (Alternate operator service provider). Organizations other than local exchange carriers (LEC) that provide operator services for long distance calling.

APCM (Adaptive pulse code modulation). A technique used to share occupied bandwidth among a maximum number of subscribers during peak times by reducing the signal sampling rates of each subscriber.

API (Application Program Interface). A programmating interface used for the inter-programming of communications or interfaces between protocol layers.

Application. Software that performs tasks for the user directly, for example, database applications or word processors.

Application Layer. The seventh layer of the OSI model, which contains user applications, and serves as the interface between the user and the communications technology.

AR (Alternate Route). A secondary path for signal transmission if the primary path is unavailable.

Architecture. The description of how a system's component parts interact and the protocols and interfaces used for communication throughout the system.

Area code. A number dialed before the desired telephone number that allows the subscriber who is outside a specific area to connect directly with the desired number.

ARIB: Association of Radio Industry and Business. ARIB is a Japanese standards organization.

ARP (Address Resolution Protocol). Provides the rules for mapping an IP address to a physical machine address, using a correlation table.

ARQ (Automatic Retransmission reQuest). A request by a receiver, for the transmitter to retransmit a data block in which errors have been detected.

Artifact. Imperfections that can arise during the processing of digital signals.

ASCII. A parity-bit code approved by ANSI to establish a uniform means of communication between data processing systems, communications systems, and terminal equipment.

Asymmetrical modulation. A technique used for high-speed transmission where a modem uses most of the bandwidth in a call for transmission, while using only a small part for reception.

Asynchronous Time Division Multiplexing. A multiplexing technique in a transmission capability is organized into unassigned time slots. The time slots are assigned to cells upon request of each application's instantaneous real need.

ATM (Asynchronous Transfer Mode). A standard for high-speed transfer of integrated media types - voice, video, and data - all on the same communications medium. ATM is a connection-oriented technique that requires information to be buffered and then placed in a cell. When there is enough data to fill the cell, the cell is then transported across the network to the destination specified within the cell. ATM cells are much smaller than standard packet-switched networks, which means that less bandwidth is required for signal transmission.

AT&T. A long distance inter-exchange carrier in the United States.

ATM Cell. A unit of transmission in ATM. A fixed-size frame consisting of a 5-octet header and a 48-octet payload

ATM Layer Link. A section of an ATM Layer connection between two adjacent active ATM Layer entities.

ATM Link. A virtual path link (VPL) or a virtual channel link (VCL).

ATM Peer-to-Peer Connection. A virtual channel connection (VCC) or a virtual path connection (VPC).

ATS (Abstract Test Suite). A set of abstract test cases designed to test a particular protocol.

Attenuation. The weakening of transmitted signals as they travel further from their point of origin. Attenuation occurs in both analog and digital systems.

AU (Alternate Use). The ability to alternate between various communications services, for example, from voice tranmission to data transmission.

Author. A person or software program that generates WML or WMLScript .

AVD (Alternate Voice Data). A single tranmission facility that can be used for either voice transmission or data transmission.

AuC (Authentication Center). A component of the infrastructure equipment in the GSM network. Its purpose is to validate subscribers logging on to the network. It does this by means of a secret key. The AuC contains a unique key (code) for each subscriber in a network. The subscriber has a copy of this key within the SIM card. A subscriber attempting to log on to the network is sent a copy of a random number by the AuC. The secret key within both the SIM card and the AuC changes their copy of the number. The number produced by the SIM card is returned to the AuC and if it is the same as the number produced by the AuC the subscriber is validated and is allowed access to the network.

Audible signal control. The controlling of the volume of set signals such as the ringing signal and dial tones.

Audio frequencies. Frequencies that can be heard by the human ear, normally between 30 Hz and 20,000 Hz.

Azimuth. The angle of a satellite in the horizontal plane, in degrees east-of-true-north.