Virtual Conferencing Glossary

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ADC (Analog-to-Digital Conversion) - The process of converting analog signals to a digital representation. DAC represents the reverse translation.

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

AGC (Automatic Gain Control) - Algorithm to normalise volume regardless of a speaker’s position relative to a microphone.

Algorithm - A computational procedure that includes a prescribed set of processes for the solution of a problem in a finite number of steps. The underlying numerical or computational method behind a code or process. Algorithms are fundamental to image compression as they allow an information-intensive file or transmission to be squeezed to a more economical size.

AMI (Alternate mark inversion) - The binary modulation code used by telephone companies for data and digital voice transmission. AMI uses RZ coding in an alternate bipolar scheme, with logical zeros corresponding to 0 V, and logical ones alternating between + 3 V and - 3 V. Self synchronisation is possible with this approach, but the number of continuous zeros must be limited.

Analog signal - A type of signal that encodes voice, video, or data transmitted over wire or through the air, and is commonly represented as an oscillating wave. An analog signal can take any value in a range and changes smoothly between values, as opposed to digital signals, which is characterized by discrete bits of information in nu-merical steps. An analog signal can transmit analog or digital data.

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

API (Application Programming Interface) - A software application used to request and carry out lower-level services performed by a computer operating system or a telephone system operating system.

Application - An application is a software program that performs a particular useful function for a user. Examples include word processing, spread sheets, distance learning, document conferencing, and Telemedicine.

Application Sharing - This is a feature that allows two or more people to work together when one the individuals does not have the same application, or same version of the application. In application sharing, one user launches the applica-tion and it runs simultaneously. Both users can impute information and otherwise control the application us-ing the keyboard and mouse. Files associated with the application can be easily transferred, so the results of the collaboration are available to both users immediately. The person who launched the application can lock out the other person from making changes, so the locked-out person sees the application running but cannot control it.

Application Viewing - In personal conferencing, the users sharing the application can see every keystroke or mouse movement made by the one user who is running the application. The other users have no control over the application.

ASCII (American Standard Code for Information Interchange) - A digital coding scheme that is capable of representing 256 characters. ASCII is a 7-level code for asynchronous character transmission over a network. It is a "uni-versal" code; for instance, a file that uses another coding scheme can nearly always be saved as an ASCII text so other systems that use other coding schemes can get at the data. With 7-level ASCII, an eighth bit can be used for parity checking that can be defined as odd or even.

ATM (Asynchronous Transfer Mode) - High speed (up to 155 mbps), high bandwidth, low-delay, transport technol-ogy, integrating multiple data types (voice, video, and data). ITU has selected ATM as the basis for the future broadband network because of its flexibility and suitability for both transmission and switching. May be used in the phone and computer networks of the future.

Asynchronous Transmission - A mode in which the sending and receiving serial hosts know where a character begins and ends because each byte is framed with additional bits, called a start bit and a stop bit. A start bit indicates the beginning of a new character; it is always 0 (zero). A stop bit marks the end of the character. The time interval between characters may be of varying lengths. Synchronous data uses an external reference clock to unify both ends of the data circuit.

Audio - In video communications, electrical signals that carry sounds. The term is also used to describe systems con-cerned with sound with recording and transmission; speech pickup systems, transmission links that carry sounds, amplifiers and the like.

Audio Bridge - Equipment that mixes multiple audio inputs and feeds back composite audio to each station after removing the individual station's input.

Authentication - A method of checking or confirming a user's personality. A username/password system or a Kerberos ticket are examples authentication methods.

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