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To use the glossary, simply click on the first letter of
the term of interest below:
A
- AAL
- ATM Adaptation Layer, the interface layer between
services and ATM.
- AAR (Automatic Alternative Routing)
- A system for providing continued telecommunications service
in the event that a primary transmission route fails catastrophically (e.g.,
when a FOTS cable is cut).
- Acoustic Echo Canceller (AEC)
- A full-duplex audio technology used to eliminate acoustically
coupled return echoes within a teleconference room. AECs model a room's
acoustics (primarily reverberation time and amplitude) and apply the inverse to
the outgoing signals to remove artifacts of the incoming signal, enhancing a
room's apparent echo return loss. Technologies used may include an AFIRF,
center clipper, noise reducer, TEC, AGC and mild echo suppression. See also
tail time, echo suppressor and echo return loss enhancement.
- ACR
- Absolute Category Rating, an ITU-T P.800 subjective
listening test performed by HEI.
- ACSB
- Amplitude Companded Single sideBand, an LMR technology
providing voice channels with 5 KHz spacing at 218-220 MHz in the USA.
- ActiveX
- A set of Microsoft plug-in program software devices or
program modules. When embedded in web pages, often used to add multimedia
functionality to the web browser.
- ADPCM
- Adaptive Differential Pulse Code Modulation.
Differential pulse code modulation that also uses adaptive quantizing; an audio
coding algorithm providing a modest degree of compression together with good
quality.
- ADSL
- Asymmetrical Digital Subscriber Line, a modest speed,
limited distance, local access solution using a single regular telephone pair.
Although an 8 Mbps maximum is theoretically possible, with a maximum return
path of 800 Kbps, a 2004 survey showed that in North America, the average bit
rate from CO to the subscriber is only about 500 Kbps. The path length cannot
exceed 5.5 Km or 3.4 miles. Supports simultaneous transmission of data and
voice over the same pair.
- AFIRF
- Adaptive Finite Impulse Response Filter, a time domain
filter, important in acoustic echo cancellers (AEC) and in removal of some
types of noise from sound signals.
- AGC
- General Usage: Automatic Gain Control
-
- T.120 Usage: AudioGraphic Conferencing
- AGT
- AudioGraphics Terminal
- Algorithm
- In audio, video and data coding, the step-by-step
mathematical process or procedure (often including repetition) providing
suitable encoding, compression and/or encryption for a specific application.
When used for either lossless or lossy compression, a significant reduction in
the number of bits required for transmission takes place.
- Alias, Aliasing
- A false signal produced by the analog-to-digital sampling
process, often caused by failure to observe the Nyquist criterion,
creating subjectively disturbing artifacts.
- AM
- Amplitude Modulation, as in the AM broadcast
band
- AMI
- Alternate Mark Inversion, a 1's density control mechanism for T1 and E1 systems. See also B8ZS and HDB3.
- AMSS
- Aeronautical Mobile Satellite Service
- Analog Signal
- Signal in which the amplitude value varies with time.
- ANI
- Automatic Number Identification, in telephony.
- ANSI
- American National Standards Institute, a globally recognized
organization issuing IT and computing technical standards.
- API
- Application Programming Interface, a set of software
routines useful for interfacing between high level systems (such as users) and
low-level systems (such as operating systems or system level tasks). Often the
design basis for a man-machine interface.
- ARS
- Automatic Route Selection, an important component of an
automatic least-cost routing system.
- Artifact
- Spurious effects or imperfections introduced into a signal as
a result of digital signal processing.
- ASIC
- Application-Specific Integrated Circuit
- ASCII
- American Standard Code for Information Interchange. A
standard set of alphanumeric and control codes representing unformatted text,
which can be represented by a single byte, developed by the USA Standards
Institute. In telecommunications, ASCII is often the coding used for the
control of telecommunications equipment. HTML tags and URLs are examples of use
of ASCII.
- ASP
- Application Service Provider, a company that provides
third-party services and software over the Internet.
-
- Active Server Page, a type of web page that is an
interface with one type of program that runs on a web server, often providing
custom content for users. Used commonly for e-commerce.
- Asynchronous
- With reference to video and data signals and devices: not
being precisely in step, not of the same frequency, or not happening together
in time.
- "AT" Instruction Set
- ATtention: A standard modem control command-set protocol
developed by modem-manufacturer Hayes, used by most modem manufacturers.
- AT&T
- American Telephone & Telegraph Company, a major US common
carrier.
- ATM
- Asynchronous Transfer Mode, a digital transmission network
technology using 53-byte packets or cells plus packet- and circuit-switched
technologies. ATM may be used for high-speed LANs and WANs.
- Availability (telecommunications use)
- A numeric representation of the period of time that a
transmission facility performs better than some minimum performance value,
usually expressed as a percentage of time on an annual basis. Performance
values are usually specified based on bit-error-rate (BER) thresholds for
digital channels and weighted signal-to-noise ratio for analog channels.
High-quality networks will have an availability of about 99.96% or better. The
statistical distribution of outages and degraded performance depend upon the
nature of the transmission media involved.
- AVT
- AudioVisual Terminal
To use the glossary, click on the first letter of
the term of interest:
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