Angstrom

A measure of optical wavelength equal to one hundred-millionth of centimetre. This unit of measure is being replaced by nanometres.

Procedure used in T1 transmission facilities in which each of the 24 T1 subchannels devotes 1 bit of every sixth frame to the carrying of supervisory signalling information. Also called 24th channel signalling.

Authentication, Authorization, Accounting

Short for authentication, authorisation and accounting, a system in IP-based networking to control what computer resources users have access to and to keep track of the activity of users over a network.  AAA services often require a server that is dedicated to providing the three services. RADIUS is an example of an AAA service.  (Pronounced "triple a")

ATM Adaptation Layer

The AAL enables engineers to adapt the ATM layer to particular services. It lies between the ATM layer and the higher layers and maps or adapts the functions or services of the higher layers onto a common ATM bearer service.

Automatic Alternative Routing

A system for providing continued telecommunications service in the event that a primary transmission route fails catastrophically.

AppleTalk Address Resolution Protocol

Protocol in the AppleTalk protocol stack that maps a data-link address to a network address.

4-bit telephony signalling coding in which each letter represents 1 of the 4 bits. This is often associated with CAS or robbed-bit signalling on a T1 or E1 telephony trunk.

Advanced Ball Grid Array

Chip package

Asynchronous Balanced Mode

HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to-point communications between two stations, where either station can initiate transmission.

Available Bit Rate

QoS class defined by the ATM Forum for ATM networks. ABR is used for connections that do not require timing relationships between source and destination. ABR provides no guarantees in terms of cell loss or delay, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the status of the network and its capability to successfully deliver data.

Area Border Router

Router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas.

Alternative Billing Services

These are IN services that allow subscribers to charge a call to a number or telephone other than the one they are using-for example, by using a charge card, credit card or personal identification number.

Access Charge

Monies collected by local telephone companies for use of their circuits to originate and terminate long-distance calls. Access charges can be per minute fees levied on long-distance companies; subscriber line charges (SLCs) levied directly on regular local lines; fixed monthly fees for special telephone company circuits such as WAL, DAL, and T-1; or special access surcharges levied on special access circuits.

A collection of thresholds assigned to circuit performance parameters. When used during circuit testing, it automatically reports whether a particular performance parameter has failed.

(1) The method, time, circuit, or facility used to enter the network.
(2) The service provided by local exchange carriers or alternate access providers, that connects an interexchange carrier with its customers. Switched access provides such service over the public switched network; special access provides dedicated access for private line services and sometimes at the closed end of switched services.
(3) To retrieve information from a storage medium. such as videodisc, CD-ROM, computer disc or videotape.

The ability of a communications network to provide bandwidth dynamically so users will receive service regardless of the bandwidth their service request requires.

A digit or digits presented to telecommunications equipment that permits the user to connect to a given service. In private branch exchange (PBX) operation, access code is the digits that are dialled connecting a telephone user to a specific trunk group or to a special service such as paging or dictation. The term is also frequently applied to the "1" dialled in many local telephone company areas for the completion of an interexchange toll call.

List kept by routers to control access to or from the router for a number of services (for example, to prevent packets with a certain IP address from leaving a particular interface on the router).

In local area networks, the technique and/or program code used to arbitrate the use of the communications medium by granting access selectively to individual stations. Examples are carrier sense multiple access/collision detection (CSMA/CD) and Token Passing.

An access device with built-in basic routing protocol support, specifically designed to allow remote LAN access to corporate backbone networks. Not designed to replace backbone routers or to build backbone networks.

The total time required to find, retrieve, and display data after initiation of a retrieval command. Access time is usually measured at its worst, or the longest possible time it takes to get from one section of the medium to another. This is generally a matter of minutes on videotape two or fewer seconds on videodisc or CD, and milliseconds or microseconds on a computer.

Automatic Call Distribution

Large scale telephone switch with software that has a high degree of intelligence geared toward routing calls; allows you to determine how you want calls routed within the support unit and provides management reports

A system in which telephone ringing uses alternating current to operate a ringer and direct current to stop the ringing when the called party answers.

Automatic Call Distribution Systems

Used by telephone companies and private businesses for managing high volumes of incoming calls.

Advanced Communications Function

IBM software products that incorporate IBM's system network architecture (SNA) and administer intercommunications between computers.

Automatic Cash Handling

Mechanized processes for accepting payment from a customer (such as credit card, debit card, wire transfer, etc.).

Acknowledgment Code

A method in which one or more characters are generated at a receiving device to indicate the information has been received correctly.

Allowed Cell Rate

Parameter defined by the ATM Forum for ATM traffic management. ACR varies between the MCR and the PCR, and is dynamically controlled using congestion control mechanisms.

Asynchronous Communications Server

A LAN server that enables a network user to dial out of the network and into the public switched telephone network (PSTN), or to access nailed-up lines for asynchronous communications. An asynchronous communications server is also called a dial-in/dial-out server or a modem server.

Association Control Service Element

OSI convention used to establish, maintain, or terminate a connection between two applications.

Multiported device that amplifies LAN transmission signals.

Administrative Domain

Group of hosts, routers, and networks operated and managed by a single organization.

A technique that allows a modem to continuously analyze and compensate for variations in the quality of a telephone line.

A form of routing in which messages are forwarded through the network along the most cost-effective path available. Messages are automatically rerouted as required by changes in the network topology if, for example, a circuit becomes disabled.

Access Deficit Charge

Advanced Data Communications Control Protocol

ANSI standard bit-oriented data link control protocol.

A set of numbers that uniquely identifies something: a workstation on a LAN, a location in computer memory, or a packet of data travelling through a network.

A 32-bit-long mask used to select an Internet protocol (IP) address for subnet addressing. The mask selects the network portion of the IP address and one or more bits of the local area network (LAN) address.

Facilities interconnection of multiple networks that each have their own address plan.

The process of converting external addresses into standardized network addresses and vice versa.

A client setting that provides independent peer-to-peer connectivity in a wireless LAN. An alternative set-up is where PCs communicate with each other through an Access Point. See AP and Infrastructure Mode.

Add Drop Multiplexer

In OSS, a multiplexer that allows a signal to be added into or dropped out of a SONET span.

Administrative Management Domain

X.400 Message Handling System public carrier. The ADMDs in all countries worldwide together provide the X.400 backbone.

The submarine cable between France and Greece.

Adaptive Differential Pulse Code Modulation

Process by which analogue voice samples are encoded into high-quality digital signals.

Asynchronous Data Switching

A private branch exchange (PBX) system that supports asynchronous data.

Asymmetric Digital Subscriber Line

A digital local loop typically using copper facilities and providing greater bandwidth in one direction than the other. ADSL is expected to provide a voice channel for calls over the public switched network, a bi-directional low-speed data channel, and a unidirectional 1.5 Mbps channel between the central office (CO) and the customer premise.

Automatic Dialling Unit

A device that is programmed with frequently called numbers. The caller presses one to three digits and the pre-programmed number is automatically dialled into the telephone circuit.

The submarine cable between Greece and Crete.

Analogue Front End

American Federation of Information Processing Societies

An organization of computer-related societies. Members include the Association for Computer Machinery, the Institute of Electrical and Electronic Engineers (IEEE) Computer Group, Simulation Councils, Inc., and American Society for Information Science.

Automatic Gain Control

A process that levels out high and low levels of sound to improve the consistency of the recording.

In Network Management Systems (NMS), process that resides in all managed devices and reports the values of specified variables to management stations.

Software that processes queries and returns replies on behalf of an application.

The total bandwidth of channel carrying a multiplexed bit stream.

An independent entity that brings several subscribers together to form a group that can obtain long-distance service at a reduced rate. Subscribers are billed by the original interchange carrier (IXC). The aggregator only provides the initial set-up of the plan, and usually provides no service after that. An aggregator is not a reseller.

Authentication Header. A field that follows the IP header in an IP datagram and provides authentication and integrity checking for the datagram.

Artificial Intelligence

The capacity of a device to perform human intelligence functions, such as reasoning, learning, and self-improvement.

Ascend Inverse Multiplexing Protocol

An in-band protocol used to manage the interconnection of two remotely located inverse multiplexers.

Advanced Intelligent Network

A switched voice and data network consisting of a variety of network elements. It refers to open interfaced, multi-vendor, telecommunications capabilities that let phone companies create and customize their service offerings. Also, often used as shorthand for the next-generation INs.

Asynchronous Input/Output

Automatic Identification of Outward Dialling

A hardware system or private branch exchange (PBX) feature that automatically obtains the identity of a calling station over a separate data link for automatic message accounting.

Alarm Indication Signal

In a T1 transmission, an all-ones signal transmitted in lieu of the normal signal to maintain transmission continuity and to indicate to the receiving terminal that there is a transmission fault that is located either at, or upstream from, the transmitting terminal.

Notification of an event with a defined severity level. SNMP message notifying an operator or administrator of a network problem.

Automatic Line Build Out

A method to ease data service unit (DSU) and channel service unit (CSU) installation by enabling the DSU/CSU to adjust signal output automatically according to line distance.

A set of instructions or mathematical formulas used to solve a given communications problem. In audio, video and data coding, the step-by-step procedure (often including repetition) which provides suitable compression and/or encryption for the specific application. When used for compression, this mathematical process results in a significant reduction in the number of bits required for transmission and may be either lossless or lossy.

A false signal produced by the analogue-to-digital sampling process. Often caused by failure to observe the Nyquist criterion and can create artifacts which are subjectively disturbing. A name that users can use on a bulletin board that is not their own. Also called handle.

A form of image distortion associated with signal sampling. A common form of aliasing is a stair-stepped appearance along diagonal and curved lines.

ATM Layer Multiplexer

The submarine cable that links Algeria, Palma, and Spain.

A form of local access where the provider is not the local exchange carrier (LEC) but is authorized or permitted to provide local access service.

Local exchange carriers that compete directly with the regional Bell operating companies (RBOCs). They are normally found only in the larger metropolitan areas. Examples are Teleport and Metropolitan Fibre Systems.

Amplitude Modulation

The technique of varying the amplitude or wavelength of a carrier wave in direct proportion to the strength of the input signal while maintaining a constant frequency and phase.

Automatic Messaging Accounting

In OSS, the automatic collection, recording, and processing of information relating to calls for billing purposes.

AMA Data Networking System

In OSS, the next generation (formerly Bellcore) system for the collection and transport of AMA data from central office switches to a billing system.

Alternative Mark Inversion

Line-code type used on T1 and E1 circuits. In AMI, zeros are represented by 01 during each bit cell, and ones are represented by 11 or 00 alternately, during each bit cell. AMI requires that the sending devices maintain ones density. Ones density is not maintained independently of the data stream. Sometimes called "Binary Coded Alternate Mark Inversion."

The submarine cable between France and Morocco.

Maximum value of an analogue or a digital waveform.

Advanced Mobile Phone Service

A North American standard for mobile telephones.

A device or method that uses non-discrete variations in frequency, amplitude, location, and so forth to symbolize or carry sounds, signals, mathematical data, or other information. Analogue technology mimics information so that a voice is represented as an electrical signal with frequency and amplitude proportional to the pitch and volume of the voice. Traditional telephone and video are both analogue technologies.

A channel that imposes no specified limits on transmitted data. There are no discrete packages or pulses of information.

A test that checks whether the modem or data terminal equipment (DTE) is causing errors in data transmission. During an analogue loopback, the system sends data between the local modem and the local DTE. Errors in transmission indicate a problem with the modem, DTE, or the interface between them.

Signal transmission over wires or through the air in which information is conveyed through the variation of some combination of signal amplitude, frequency, and phase.

All Number Calling

Telephone calling numbers containing all numerical digits instead of a combination of two letters and five numbers.

Automatic Number Identification

SS7 (signalling system 7) feature in which a series of digits, either analogue or digital, are included in the call, identifying the telephone number of the calling device.

The submarine cable between France and Tunisia.

Allows a user to retrieve documents, files, programs, and other archived data from anywhere on the Internet without having to establish a user ID and password. By using the special user ID of anonymous, the network user will bypass local security checks and will have access to publicly accessible files on the remote system.

American National Standards Institute

ANSI creates standards for networking and communications. It is the U.S. representative to the International Standards Organization (ISO)

The submarine cable between Senegal and Morocco.

In ATM, an address that can be shared by multiple end systems. An anycast address can be used to route a request to a node that provides a particular service.

The submarine cable that links Australia, New Zealand, and Canada.

All Ones Code

A signal stream containing 15,360 or less zeros in one second. When a device loses synchronization, it sends an all ones code to keep the network up. It also sends this code to tell the network there is a transmission problem.

Alternative Operator Services

Business not associated with the telephone company that provides operator services, for example, to private pay phone companies.

Access Point

A hardware device, or software used in conjunction with a computer, that serves as a communications "hub" for wireless clients and provides a connection to a wired LAN. An AP can double the range of wireless clients and provide enhanced security.

Access Provider Architecture

The specifications of a system and the method in which its subcomponents interconnect, interact, and cooperate. Architectures are often described in multiple levels of abstraction from low-level physical to higher-level logical application and end-user views.

Avalanche Photo Diode

Application Programming Interface

A programming interface for accessing and administering ISDN services

Advanced Private Line Termination

An AT&T term referring to a private branch exchange (PBX) user's ability to access all the services of an Enhanced Private Switched Communications Services (EPCS) network.

The submarine cable between Australia and Papua New Guinea.

Asia Pacific Network Information Centre

Non-profit Internet registry organization for the Asia Pacific region. The other Internet registries are currently IANA, RIPE NCC and Inter NIC.

The point in a satellite's orbit that is farthest from the earth.

The submarine cable between Greece and Cyprus.

Advanced Program-to-Program Communications

A set of IBM protocols also known as LU 6.2 and Type 2.1 architectures. It functions within SNA's APPN to support peer to-peer communications between workstations attached to SNA LANs and the applications running on those workstations. It was added to SNA as part of the "new" SNA to support peer to-peer networking, unlike the traditional hierarchical SNA approach in which the mainframe acts as host or master and treats the other computer as a terminal or slave.

Apple Computer's proprietary local area network (LAN) protocol suite for linking Macintoshes and peripheral devices. AppleTalk is a carrier sense multiple access/collision detection (CSMA/CA) network with 115 Kbps data rate and allows connecting up to 32 devices.

A software program running on top of the operating system (Windows, UNIX, Mac) that has been created to perform a specific task for a user. Examples include word processing software like Word/Word Perfect, spreadsheets like Excel or Lotus 123, home finance packages like Quicken, etc.

Advanced Peer-to-Peer Networking

Enhancement to the original IBM SNA architecture. APPN handles session establishment between peer nodes, dynamic transparent route calculation, and traffic prioritization for APPC traffic.

Next generation APPN that reduces the label-swapping routing algorithm with source routing. Also called "high-performance routing"

Automatic Protection Switching

SONET switching mechanism that routes traffic from working lines to protect them in case of a line card failure or fibre cut.

Alternate Route

A secondary communications path to a destination when the primary path is unavailable.

Access Rate

The data rate of the user access channel. The speed of the access channel determines how rapidly (maximum rate) the end user may inject data into the network.

Automatic Ring Down

A private line connecting a station instrument in one location to a station instrument in a distant location with automatic two-way signalling. The automatic two-way signalling used on these circuits causes the station instrument on one end of the circuit to ring when the station instrument on the other end goes off-hook. This circuit is sometimes called a "hot-line" because urgent communications are typically associated with this service. ARD circuits are commonly used in the financial industry. ARD circuits also have one-way signalling, where station A rings station B when station A goes off hook, but station B cannot ring station A.

American Registry for Internet Numbers

Non-profit organization for the purpose of administrating and registering IP numbers to the geographical areas currently managed by Network Solutions (InterNIC). Those areas include, but are not limited to, North America, South America, South Africa, and the Caribbean.

Asynchronous Response Mode

HDLC communication mode involving one primary station and at least one secondary station, where either the primary or one of the secondary stations can initiate transmissions.

Address Resolution Protocol

This portion of the TCP/IP protocol maps an IP address to the physical address (Ethernet address) of the PC that it is on, helping to identify PCs on an Ethernet LAN

Advanced Research Projects Agency

The U.S. Department of Defence agency that supports the ARPAnet resource-sharing computer network.

Advanced Research Projects Agency Network

The Advanced Research Projects Agency Network developed by the eponymous research agency in the 1960s as the first, large scale, packet switched network. It is still I in use today, connecting a large number of universities in the US and Europe, as well as commercial users.

Automatic Repeat Request

Communication technique in which the receiving device detects errors and requests retransmissions.

The submarine cable between France and Greece.

Alarm Relay Unit

Answer Supervision

An electrical signal the local telephone company at the distant end of a long-distance call sends back up the line to indicate positively the call has been answered by the called party. The signal tells billing equipment to start timing the call.

Analogue Signal

A signal, in the form of a continuous varying physical quantity such as voltage, that reflects variations in some quantity, such as loudness in the human voice.

Any Service, Any Credit

ATM Subscriber Access Multiplexer

A telephone central office multiplexer that supports SDL ports over a wide range of network interfaces. An ASAM sends and receives subscriber data (often Internet services) over existing copper telephone lines, concentrating all traffic onto a single high-speed trunk for transport to the Internet or the enterprise intranet. This device is similar to a DSLAM (different manufacturers use different terms for similar devices).

American Standard Code For Information Interchange

ASCII is a character-encoding system for local area networks (LANs). The 128 standard ASCII characters are composed of seven bits, and have the values 0-127. The extended ASCII character set contains another 128 values.

Agent-Set Control Unit

The submarine cable between Indonesia and Singapore.

The submarine cable between The Philippines and Singapore.

ATM Service Interface

Application Specific Integrated Circuit

Automated Security Incident Measurement. Monitoring of network traffic and collection of information on networks by detecting unauthorized network activity.

Auxiliary Signal Network

Application Service Provider

A company providing IT services for users who do not want to run all their own IT activities. ASPs run enterprise software on their own computers; companies access this over a telecommunications network. This field of activity can be referred to as applications hosting.

Access Service Request

A document or data transaction sent to the local exchange carrier (LEC) to order the local access portion of a circuit.

Application Specific Standard Product

Term describing digital signals that are transmitted without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and end of each character.

All Trunks Busy

A single tone interrupted at a 60 or 120 impulses-per-minute (ipm) rate that indicates all lines or trunks in a routing group are busy.

Adaptive Transform Coding

A voice coding technique used between 9.6 kbps and 32 kbps.

Asynchronous Time-Division Multiplexing

Method of ending information that resembles normal TDM, except that time slots are allocated as needed rather than pre-assigned to specific transmitters.

The submarine cable between Portugal and Brazil.

Asynchronous Transfer Mode

A method of communications in which information is transmitted in "cells". Transmission rates from 150 megabits per second to 600 mbps are under consideration.

Point in an ATM network where an ATM connection is initiated or terminated. ATM endpoints include ATM-attached workstations, ATM-attached servers, ATM-to-LAN switches, and ATM routers.

ATM standardization organisation

Service-independent sub-layer of the data link layer in an ATM network. The ATM layer receives the 48-byte payload segments from the AAL and attaches a 5-byte header to each, producing standard 53-byte ATM cells. These cells are passed to the physical layer for transmission across the physical medium.

Asynchronous Transfer Mode Switch

Switch using a transfer mode in which the information is encapsulated into cells. It is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic.

ATM Management

Process that runs on an ATM switch that controls VCI translation and rate enforcement.

ADSL Termination Unit - Remote/Central Office

Alternative Use

The ability to switch communications facilities from one type to another, such as voice to data.

Acceptable Use Policy

Many transit networks have policies that restrict the use to which the network can be put. Enforcement of AUPs varies with the network.

ATM User Service Module

The Australian telecommunications regulatory body.

A specialized form of an Interactive Voice Response system.

A system that permits restart of the switched message flow after a fatal system failure. The recovery process is started by an operator response when the system is reloaded, and works from special records saved in the communications data bank.

Alternate Voice Data

A single transmission facility that can be used for either voice or data.

Audio Video Interleave

A specification that allows for the capture and storage of video and waveform audio in a single data stream. Because of speed and memory limitations, AVI offers only rough animation, not full-motion video.

ATM Voice Multiplexer

Automated Voice Response

A computer assisted answering system which provides pre-recorded or real-time information based on touch tone phone inputs from the customer. Benefits include immediate access into the system (using an account number or password) and 24 hour availability.

Administrative Weight

Value set by the network administrator to indicate the desirability of a network link. One of four link metrics exchanged by PTSPs to determine the available resources of an ATM network.

American Wire Gauge

The US standard for wire size specification.

ATM Wireless Multiplexer

Reunion base station node