Telecommunications Glossary - tecweb.org

1 Telecommunications Glossary /131 Segovia, San Clemente, CA 92672(949) 369-3867 file can be found on the TEC website Glossaryfrom "A Technical Guide to Teleconferencing andDistance Learning," 3rd editionA2N59B7O62C13P64D22Q70E28R71F31S7 4G36T83H38U88I42V90J46W93K48X95L49Y95M52 Z95 Telecommunications Glossary /2 AAccess Channels: Dedicated channels giving nondiscriminatory access to a localcable system by the public, government agencies or educational institutions. ACCUNET Switched Digital Services: High-speed dial-up digital data services offeredby AT&T for full duplex digital transmission at speeds of 56, 64, 384 and 1536 include data, voice and video services. Acoustic Coupler: A device that allows a conventional telephone handset to feed itssignal into a modem, as opposed to direct couplers, which feed themodulated/demodulated signal directly into the phone Echo Canceller: All speakerphones have some form of adaptive echocanceller that produces a synthetic replica of the potential echo to subtract from thetransmit audio.

2 Most units have a center clipping echo suppresser to remove theresidual echo from the transmit signal. The goal of the acoustic echo canceller is toreduce the amount of direct and reverberant loudspeaker coupling to the microphone toprevent echo. To achieve this, the algorithms used in today's devices require an audiosystem that is feedback stable. Acoustic Echo Return Loss - AERL: The minimum loss experienced by a sound intraveling from the loudspeaker to the microphone in a conference room. It is expressedin dB or decibels. A 0 dB loss corresponds to a perfectly reflective room or to very closecoupling between loudspeaker and microphone. In practice, AERL figures can rangefrom 0 to -30 dB, with a poor room having the former Echo Return Loss Enhancement - AERLE: The maximum echocancellation provided by the acoustic canceller.

3 Typical figures will vary from 6 to 18 larger the number the better. It is important to note whether the figure is quoted withthe center clipper enabled or disabled. If quoted with center clipper disabled, it is a truemeasure of the cancellation provided by the echo canceller rather than the attenuationprovided by the center clipper. Acoustic Modem: A modulator-demodulator unit that converts data signals totelephone tones and back again. Active satellite : A satellite that transmits a signal, in contrast to a passive satellite thatonly reflects a signal. The signal received by the active satellite is usually amplified andtranslated to a different frequency before it is Hoc: Teleconferencing technology and sites assembled for an event; equipmentmay be rented or permanently installed; sites are not always part of the network.

4 Addressable: The ability to signal from the headend or hub site in such a way that onlythe desired subscriber's receiving equipment is affected. This makes it possible to senda signal to a subscriber and effect changes in the subscriber's level of service such asthe ability to receive a Glossary /3 ADPCM - Adaptive differential pulse code modulation: A method of compressingaudio data by recording the differences between successive digital samples rather thanfull value of the samples. There are many different types of ADPCM standards; thisrefers to the standard as defined in the CD-ROM XA and CD-I - Asymmetric Digital Subscriber Loop: ADSL uses a regular phone line(twisted pair) without a dial tone (a dry pair) to allow transfer speeds of up to 7 Mbdownstream with slower speeds going back up (faster than a T1).

5 The Telcos are usingADSL to maintain market share rather than allowing the cable industry to deploy cablemodems. Pacific Bells says that 45 percent of its customers will be able to have accessto ADSL by the end of Network: Group with their own satellite receive equipment; routinely receivesame programming. Agent: See : 1. Rule of thumb for doing something with a semblance of intelligence. Forexample, a descrambling algorithm will yield a clear, unscrambled message from anapparently meaningless one. 2. The procedure used for performing a Online - AOL: Commercial information service with a graphical : A device used to increase the strength of video and audio electronic signals. Amplitude: The size or magnitude of a voltage or current waveform; the strength of asignal.

6 Analog: Information represented by a continuous electromagnetic wave encoded sothat its power varies continuously with the power of a signal received from a sound orlight - A/D Conversion: The conversion of an analog signal into a digitalequivalent. An A/D converter samples or measures an input voltage and outputs adigitally encoded number corresponding to that voltage. Analog Transmission: Transmission of a continuously variable signal as opposed to adiscrete signal. Physical quantities such as temperature are described as analog whiledata characters are coded in discrete pulses and are referred to as : To effect motion of any sort; to animate a person's presentation. Animation: A video, film, and computer production technique utilizing cartoon-typeartwork to create the illusion of - American National Standards Institute: ANSI is one of these "terminalemulation" methods.

7 Although most popular on PC-based bulletin-board systems, it canalso be found on some Internet sites. To use it properly, you will first have to turn it on,or enable it, in your communications Glossary /4 Answerback: The response of a terminal to remote control signals. Antenna (dish) Thedevice that sends and/or receives signals (electromagnetic) from the satellite .: Antenna Power: The product of the square of the broadcast antenna current and theantenna resistance where the current is measured. Aperture: A cross section of the antenna exposed to the satellite signal. Application: The use of a technology to achieve a specific Software: In computers, programs used to interact with and accomplishwork for the user. Application software is usually written in a higher computer languagesuch as Basic, COBOL, FORTRAN or Pascal, and may be written by the user orsupplied by the manufacturer or a software Program: A computer program dedicated to a specific purpose or programs which produce discernible results and can sometimes bemachine-independent, are distinct from systems programs, which are designed to driveparticular electronic devices and are always machine-dependent.

8 Archie: A system which allows searching of indexes of files available on public serverson the : A medium that is readable and/or writable for an extended Cable: Coaxial cable that can be direct buried without protective conduit, orused in underwater : A predecessor of the Internet. Started in 1969 with funds from the DefenseDepartment's Advanced Research Projects : American Standard Code for Information Interchange; pronounced "Askee." Aneight-level code for data transfer adopted by the American Standards Association toachieve compatibility between data services. Aspect Ratio: The ratio of picture width to height (4 to 3 for North American NTSC broadcast video). Asynchronous Communication: Takes place in different time frames and accessed atthe user's convenience.

9 Synchronous communication takes place in the same timeframe such as a live teleconference. Asynchronous Time-Division Multiplexing: An asynchronous signal transmissionmode that makes use of time-division multiplexing. Asynchronous Transmission: A technique in which the time interval betweencharacters may be of unequal length. Transmission is controlled by start and stopelements at the end of each character. Used for low-speed terminal links. Telecommunications Glossary /5 ATM - Asynchronous Transfer Mode: ATM switching protocol can handle all types oftraffic - voice, data, image, and : The difference between transmitted and received power due to lossthrough equipment, lines, or other transmission devices; usually expressed in loss in power of electromagnetic signals between transmission and : A device for reducing the amplitude of a : Advanced Television Systems Committee.

10 ATV - Advanced Television: An agglomeration of techniques, based largely on digitalsignal processing and transmission, that permits far more program material to becarried through channels than existing analog systems can manage. In this sense,HDTV (high definition television) is a subset of ATV. ATV does not automatically signifyimproved picture or sound performance. Those are things that can be accomplishedwith ATV in systems designed for such purposes, but it can also carry ten somewhatlower- quality signals where only one could exist previously, or permit ghost cancellationfor ordinary NTSC signals. In each case, the new features derive from the use of digitaltechniques of one form or another. Audio Bridge: An audio bridge connects the telephones at remote sites, equalizes thenoise distortion and background noise for a live audio teleconference.