10baseT - 10 Mbps Ethernet LAN technology.

100baseT - 100 Mbps Ethernet LAN technology.

16CIF - 16 times Common Intermediate Format: 1408x1172 pixels. H.263 optional format.

4CIF - 4 times Common Intermediate Format: 704x576 pixels. H.263 optional format.

AAL - ATM Adaptation Layer. Format for sending packets on a ATM network.

AC signaling - Any in-band signaling system that uses AC current. The most common AC signaling system is DTMF. Contrast with DC signaling.

Access Device - A gateway to the ATM network. It provides entry  between various hardware and applications to the device.

Access Provider - Any organization that arranges for an individual or an organization to have access to the Internet. 

Accunet - Trademark name for high speed switched digital service provided by AT&T.

ACM - The Association for Computing Machinery (ACM), founded in 1947, is the largest and oldest international scientific and industrial computer society. Through its many Special Interest Groups (SIGs) the ACM fosters research and communication in a broad range of computing areas. 

A/D - Analog-to-digital.

Adaptive Differential Pulse Code Modulation (ADPCM) - A method of sampling and converting analog signals to digital signals. Similar to DPCM except that when a wide difference occurs between two successive samples of a signal, it uses a sophisticated algorithm to code the difference. 

ADSL - Asymmetric Digital Subscriber Line. High bandwidth network technology that transmits at a higher rate in one direction than the other. Uses standard POTS wiring for bandwidths up to several Mbps.

AGC - Automatic Gain Control. Algorithm to normalize volume regardless of speaker's position relative to microphone.

Aggregation - Method for sending data down two or more parallel channels.

A-law - European quantizing method for voice PCM in G.711.

Algorithm - Method for solving a problem or performing a task.

Analog - The traditional means of sending traffic over copper wires. Analog signals are continuously variable, like a flowing line or wave, as opposed to 1/0 digital signals. Analog signals must be converted into digital signals in order for computers to be able to understand them. Used in POTS.

Analog Gateway - A means of connecting dissimilar codec's. Incoming digital signal from one type of codec is decoded by a similar codec and converted to analog. The Analog signal is then passed to the dissimilar codec, coded, and decoded at the far end. Analog gateways achieved interoperability in a nonstandard environment, but have the disadvantages of degrading video and audio quality and often reducing functionality.

ANI - Automatic Number Identification (ANI) is a service that provides the receiver of a telephone call with the number of the calling phone. The method of providing this information is determined by the service provider (such as AT&T, MCI, Sprint, and so forth). 

ANS - Automatic Noise Suppression. Reduces background noise from an audio signal.

Annex D - Still-image graphics mode of H.261. Can support maximum 704x576 resolution.

ANSI - American National Standards Institute.

API - Application Programming Interface.

Address Resolution Protocol (ARP) - Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.

Artifact - Coding error found in compressed audio or video signal.

ARQ/ACF - Admission Request/Confirmation. Used by a gatekeeper to determine if the endpoint has permission and resources available, then return the necessary IP address to connect. 

Aspect Ratio - Ratio of horizontal to vertical picture size. 4:3 for the standard TV. 16:9 for the new wide screen formats.

Asynchronous - No constant rate. Not synchronous. A method of data transmission which allows characters to be sent at irregular intervals by preceding each character with a start bit and following it with a stop bit. The timing of the transmission is not determined by the timing of a previous character. Applications include communication between most small computers and mainframes, lower speed transmissions, and less expensive computer transmission systems.

ATM - Asynchronous Transfer Mode. A connection oriented service that transmits voice, data, and video traffic in fixed cell lengths at high speeds into the gigabit range. A high bandwidth packet-based network technology.

Automatic Call Distribution (ACD) - ACD directs incoming calls to designated stations in a specified order of priority.

Autonomous System - Internet (TCP/IP) terminology for a collection of a  gateway or router that fall under one administrative entity and cooperate using a common Interior Gateway Protocol.

B channel - 64 kbps bearer channel used for voice, circuit, or packet switched data.

Backbone - A pathway or cable that joins multiple computers across small distances ( within the same building ) or multiple LAN's across long distances.

Bandwidth - The capacity or speed of a telecommunications transmission medium. example -128kbps.

BAS - Bit-rate Allocation Sequence in H.221. Capabilities exchange uses these codes.

Baseband -  The basic direct output signal in an intermediate frequency based obtained directly from a television camera, videoconference television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a "modulator" is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.

Baud Rate - The rate of symbols per second ( not the rate of bits per second. )

Bearer service - As defined by CCITT standards, a type of telecommunication service that provides the capability for the transmission of information between user-to-network interfaces.  Bearer services defined for ISDN are circuit mode and packet mode.

Binary - A system of counting that is base-2. ( The decimal system that we use is base-10.) Unlike the decimal system which uses digits having possible values between 0 and 9, the binary system has digits ( bits ) that can only have the values 0 and 1.

B-ISDN - Broadband ISDN. Based on ATM. Can run up to several hundred Mbps.

Bit - A unit of information that contains one of two states: on or off. This is the unit of counting in the binary system.

Bitstream - Data that is transmitted between systems carrying audio, video, data, and signaling.

Blocking - Artifact found in H.261, H.263 and MPEG video coding. Picture breaks up into square sub-sections when the coder cannot produce an accurate video reproduction due to limited available channel bits and/or processing power.

Blurring - Artifact found in video when the high frequencies ( detail ) of the image are not coded.

BONDING protocol - Industry standard B channel aggregation protocol. Developed by the Bandwidth on Demand Interoperability Group. Method for making several BRI lines look like one high-rate line by use of an IMUX ( Inverse Multiplexer. )

bps - Bits per second. Defining the speed of a network connection in number of bits transmitted every second.

BRI - ISDN Basic-Rate Interface consisting of 2B+D channels.

Bridge ( bridging ) - A data communications device that connects two or more networks of compatible protocols. Multipoint Control Unit ( MCU ) that can link several videoconferencing systems for multipoint calls.

Broadband – A service or network capable of supporting a wide range of multiple transmissions (video, data or audio) at the same time.

BRQ/BCF - Bandwidth Request/Confirmation. Used by a gatekeeper to determine the bandwidth requested by an endpoint. 

Byte – 8 bits to a byte.

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