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AAL – ATM Adaption Layer

This is the protocol used on top of ATM to support high-level service requirements, converting non-ATM bit streams into ATM cells.

AAL2 – ATM Adaption Layer 2

Used for carrying both CBR traffic and VBR traffic simultaneously, usually in support of voice-over-ATM.


The service provided by local exchange carriers or alternate access providers, that connects an Interexchange carrier with its customers. There are two kinds of access services:

  • Switched access – Provides such service over the Public Switched Telephone Network.
  • Special access service – Provides dedicated access for private line services or sometimes at the closed end of switched services.

Access Line

The portion of a telephone line between the end user’s location and the telephone service provider’s central office. Also called local loop, subscriber loop or local line.

Access Tandem

A tandem switch that’s used to interconnect between carriers for equal access. Typically this used to interconnect ILECs with IXCs, but now also includes CLECs.

ADPCM – Adaptive Differential Pulse Code Modulation

An ITU-TS standard technique for voice encoding and compression, which allows analogue traffic to be carried within a 32 Kbps digital channel.

ADSL – Asymmetric Digital Subscriber Line

Simply put, ADSL allows data to be transferred quickly over your phone line’s existing copper wires, as a form of common internet connection. Your broadband provider puts a splitter into your telephone wall socket so that you can run both your telephone and your internet connection at the same time.

In contrast with legacy ‘dial-up’ connections, ADSL internet connectivity allows you to access the WWW whilst chatting on the phone simultaneously. Nearly every home in the UK can get an ADSL connection, with a speed up to 8 Mbps. The further you live from the telephone exchange, the slower the connection speed.

AIN – Advanced Intelligent Network

An evolving and service-independent architecture that allows a carrier to quickly and economically create and modify telecommunications services for its customers.

ALI – Automatic Location Identifier

A feature of 999 systems, which provides information to call agents, such as name, phone number and address.


In the SS7 world, an A-Link is a signalling link that connects an STP to an SSP or an SCP. A-Links operate at a transmission speed of 56 Kbps.

ANSI – American National Standards Institute

UA non-governmental organisation that develops and distributes standards for transmission codes, protocols and high-level languages for suggested use in the USA

API – Applications Programming Interface

API is a set of routines, protocols and tools for building software applications. The API specifies how software components should interact. They’re used when programming graphical user interface (GUI) components.

AMA – Automatic Message Accounting

The network functionality that measures, collects, formats and outputs subscriber network usage data, to upstream billing and other operating systems.

Analog Transmission

The traditional telephone technology (for voice transmission) in which sound waves (or other data) are converted into electrical impulses of varying strength or amplitude.

ANI – Automatic Number Identification

Also known as Called ID, ANI is a service provided by local exchange carriers in which the phone number of a caller is sent to the receiving party’s telephone, between the first and second ring.

It’s one of several CLASS services, all of which require SS7 interoffice signalling.

ATM – Asynchronous Transfer Mode

An international standard for high-speed broadband packet-switched networks, operating at broadband digital transmission speeds. The technology is based on fixed-length 53-byte cells.

ATM includes protocols that specify how diverse kinds of traffic are transformed into standardised packets, whose transport can be managed uniformly within the network.

Asynchronous Protocol

A type of transmission in which information is sent at random, at any speed with no routing information.

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