Glossary (A)
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AAA (AUTHENTICATION, AUTHORIZATION AND ACCOUNTING)
Authentication refers to the confirmation that a user who is requesting services is a valid user of the network services requested. Authorization refers to the granting of specific types of service (including "no service") to a user, based on their authentication, what services they are requesting, and the current system state. Accounting refers to the tracking of the consumption of network resources by users. Widely used AAA protocols are Radius and Diameter.
AAC (ADVANCED AUDIO CODING)
A standardized, lossy digital audio compression scheme and part of the MPEG-4 standard. Designed as an improved-performance codec relative to MP3. AAC is the current default iTunes codec, the media player which powers iPod. AAC is also widely available in a range of portable media players and 3G mobile handsets.
ACCOUNTING
Accounting refers to the tracking of the consumption of network resources by users. This information may be used for management, planning, billing, or other purposes. Typical information that is gathered in accounting is the identity of the user, the nature of the service delivered, when the service began, and when it ended.
ADDRESS RESOLUTION
A mechanism for identifying the address of called endpoint in terms of the network, such as and IP address.
AEC (ACOUSTIC ECHO CANCELLER)
Acoustic Echo is caused by direct and indirect feedback from speaker to microphone. An acoustic echo canceller electronically removes both direct coupling and reflected echo, enabling true full-duplex hands-free telephony for both mobile phones and desktop speakerphones.
AJB (ADAPTIVE JITTER BUFFER)
A jitter buffer is designed to remove the effects of jitter from the decoded voice or video stream, buffering each arriving packet for a short interval before playing it out. A fixed jitter buffer maintains a constant size whereas an adaptive jitter buffer has the capability of adjusting its size dynamically in order to optimize the delay/discard trade-off.
ALIAS
An alternative identification string for an IP address. An alias can be a name, a URL address, an e-mail address, a transport address in the form of “IP address:port number” or a Party Number.
ALG (APPLICATION LEVEL GATEWAY)
Serves as communicators between two networks. ALGs are protocol-aware entities that examine application protocol flows and only allow messages that conform to security policies to pass.
See also Proxy Server
ALTERNATE GATEKEEPER
Support for an Alternate Gatekeeper enables you to make Gatekeeper failures transparent to the endpoints that are registered to the Gatekeeper. In RADVISION implementations, a backup Gatekeeper (the “Secondary” Gatekeeper) runs in parallel to each online Gatekeeper (the “Primary” Gatekeeper).
AMR (ADAPTIVE MULTI-RATE)
An audio data compression scheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP.
AMR-WB (ADAPTIVE MULTI RATE – WIDEBAND)
A speech coding standard. The codec provides excellent speech quality due to wider speech bandwidth of 50 - 7000 Hz compared to narrowband speech codecs which in general are optimized for POTS wireline quality of 300-3400Hz. AMR-WB is codified as G.722.2, an ITU-T standard speech codec.
AS (APPLICATION SERVER)
An IMS element that implements service logic, such as conferencing servers. multiparty video calling and presence. The AS abstracts the underlying network architecture and protocols, enabling application developers to easily and quickly introduce new services.
ATCA (ADVANCED TELECOMMUNICATIONS COMPUTING ARCHITECTURE)
A very large specification effort with more than 100 companies participating. Known as AdvancedTCA™, the official specification designation is PICMG 3.x. AdvancedTCA is targeted to requirements for the next generation of "carrier grade" communications equipment.
ATM (ASYNCHRONOUS TRANSFER MODE)
A high bandwidth, high speed (up to 155 Mbps), controlled-delay packet switching and transmission system integrating multiple data types (voice, video, and data). Uses fixed size packets also known as "cells." ATM is often referred to as "cell relay."
AUTHORIZATION
Authorization refers to the granting of specific types of service (including "no service") to a user, based on their authentication, what services they are requesting, and the current system state. Authorization determines the nature of the service which is granted to a user.
AUTHENTICATION
The process of verifying the identity of a user trying to log on to a system, or of sender of a message.