Glossary - A

A&B

A&B bit signaling (network)
Procedure used in most T1 transmission facilities in which each of the 24 T1 subchannels devotes one bit of every sixth frame to the carrying of supervisory signaling information. Also called 24th channel signaling.
The control bit for the first six frames is the A-bit, and the control bit in the second six frames is the B-bit.

AAL

ATM Adaptation Layer (ATM)
Layer 3 of the ATM architecture. In order for ATM to support many kinds of services with different traffic characteristics and system requirements, adapts user traffic (caracterized by different classes of applications) into/from ATM 48-byte payloads. The AAL is divided into the Convergence Sublayer (CS) and the Segmentation and Reassembly (SAR) sublayer. Four types of AAL were originally recommended by CCITT. Two of these have now been merged into one. Also, within the past year a fifth type of AAL has been proposed. Each is geared to a particular class of traffic, with specific characteristics concerning delay and cell loss. All AAL functions occur at the ATM end-station rather than at the switch.

AAL1 (ATM)
Addresses CBR (constant bit rate )traffic such as digital voice and video and is used for applications that are sensitive to both cell loss and delay and to emulate TDM-based circuits (i.e. DS1, E1, conventional leased lines). It requires an additional byte of header information for sequence numbering, leaving 47 bytes for payload.

AAL2 (ATM)
First version:
Supports connection-oriented services that do not require constant bit rates. Protocol standard for supporting time-dependent Variable Bit Rate (VBR-RT) of connection-oriented traffic (i.e. packetized video and audio). This first version is now obsolete.
Second version:
Low rate services with a time constraint. It is used for voice transformations with rate compression.

AAL3/4 (ATM)
Intended for both connection-oriented and connectionless variable bit rate (VBR) services. It handles bursty connection-oriented traffic, like error messages, or variable-rate connectionless traffic, like LAN file transfers. It is intended for traffic that can tolerate delay but not cell loss; to ensure that the latter is kept to a minimum, AAL3/4 performs error detection on each cell and uses a sophisticated error-checking mechanism that consumes 4 bytes of each 48-byte payload. AAL3/4 allows ATM cells to be multiplexed. Used also to support SMDS.

AAL5 (ATM)
Trafic type used to carry bursty LAN data traffic with less overhead than AAL3/4. Also known as the Simple and Efficient Adaptation Layer (SEAL), AAL5 uses a conventional 5-byte header. Supports the transport of Lightweight Variable Bit Rate (VBR) traffic and signaling messages. Also used to support Frame Relay services. It does not support multiplexing.

ABIT

Always Be In Touch (hardware, communications)
Phone or device which permits to his user to receive electronic message no matter where he is.

ABM

Asynchronous Balanced Mode (network)
A communication mode used in HDLC and derivative protocols that allows either of two workstations in a peer-oriented point-to-point configuration to initiate a data transfer.

ABR

Available Bit Rate (ATM)
One of the two best effort service types (the other one is UBR) defined by the ATM Forum, where the network makes no absolute guarantee of cell delivery however it guarantees a minimum bit rate for user transmission. An effort is also made to keep cell loss as low as possible. ABR supports variable bit rate data traffic with flow control. ABR is one of the five ATM Forum-defined service types.

Abstract Syntax

A description of a data structure that is independent of machine- oriented structures and encodings. Source: RFC1208.

ABT

ATM Block Transfert (ATM)
Acronym used by ITU-T I.371 "ATM Transfert Capability".

Access Method (network)

Generally, the method by which networked stations determine when they can transmit data on a shared transmission medium. Also, the software within an SNA processor that controls the flow of information through a network.

Access Rate (network)

The transmission speed, in bits per second, of the physical access circuit between the end user and the network. See also bit rate.

ACD

Automatic Call Distribution/Distributor (network, phone)
A specialized phone system to distribute high volume of calls evenly or according to priority to minimize waiting time, or to route calls to appropriate parties.
An ACD might direct calls to agents whose lines are not busy. Alternatively, an ACD might direct calls based on what a caller selects by pressing the telephone keypad (the caller, for example, might respond to recorded system prompts to enter an account number or choose a service option).

ACK

Acknowledgement (network)
Portion of any communications protocol responsible for acknowledging the receipt of a transmission. ACKs can be separate packets or piggy backed on reverse traffic packets. An ACK is sent to indicate that a block of data arrived at its destination without error.

ACL

Access Control List (network)
Most network security systems operate by allowing selective use of services. An Access Control List is the usual means by which access to, and denial of, services is controlled. It is simply a list of the services available, each with a list of the hosts permitted to use the service.

ACM

Address Control Message (ATM)

Address Complete Message (ATM)
Address Complete Message, signaling packet equivalent to ring-back tone or answer.

ACP

AIMUX Control Protocol (ATM)

ACR

Allowed (or Available) Cell Rate (ATM)
The available bandwidth, in cells per second, for a given QoS class, which is dynamically controlled by the network.

Attenuation to Crosstalk loss Ratio (physical layer)

ACS

Access Control System (network)

ATM Circuit Steering (ATM)
A method of routing ATM traffic to built-in test facilities in ATM equipment for monitoring and analysis.

ACTS

Advanced Communications Technologies and Services (network)
The ACTS Programme was established under the Fourth Framework Programme of European activities in the field of research and technological development and demonstration (1994-1998). The Programme supports research and development in advanced communications in order to facilitate economic development and social cohesion in Europe. Under the Programme, individual companies, public sector organisations, research institutes, schools and universities agree to work together as individual project consortia, pooling their knowledge and resources in pursuit of specific research objectives covered by the ACTS workplan. All ACTS research is conducted in the context of usage trials to ensure relevance of the results and to encourage a broadening of awareness of the benefits that advanced communications may bring. Twenty two National Host organisations support project experiments and act as a window to the many trials which are already being conducted within the countries concerned, and also internationally.

The Programme has a budget of 671 million ECU, which is about 5% of the total budget available for European research under the Fourth Framework Programme. Given the global nature of the communications business, ACTS encourages participation from non-EU countries. Indeed organisations from anywhere in the world can participate in the Programme on a project-by-project basis without Community funding once their participation is shown to be of mutual benefit to the parties involved. Special funding arrangements presently apply to organisations from Central and Eastern Europe and from the countries of the former Soviet Union. The involvement of small and medium sized enterprises (SMEs) in the Programme is also actively encouraged. URL: http://www.cordis.lu/acts/home.html.

Active Hub (network)

A multiport device that amplifies LAN transmission signals.

AD

Administrative Domain (network)
A collection of hosts and routers, and the interconnecting network(s), managed by a single administrative authority.

Adapter (hardware)

A board installed in a computer system, usually a PC, to provide network communication capabilities to and from that computer system. Also called a network interface card (NIC).

Adapter Card (hardware)

Circuit board or other hardware card in DTE that provides the physical interface between the computer (DTE) and the physical network circuit (see also NIC), usually applied to an add-in card in a PC, workstation, router, or similar equipment.

Address (network)

Digital information that uniquely identifies networks, stations, and devices so that each can send and receive messages.

Internet Address (network, Internet)
There are four types of addresses in common use within the Internet:

• email address: name@mail_server.domain
• IP adress or Internet address: a.b.c.d or device_name.sub-domain.domain
• hardware or MAC address
• Uniform Resource Locator (URL): method://server_adress[port]/document_path

Address Mask - Subnet Mask (network, Internet)

A bit mask used to identify which bits in an IP address correspond to the network and subnet portions of the address.
This mask is often referred to as the subnet mask because the network portion of the address (i.e., the network mask) can be determined by the encoding inherent in an IP address.

Address Resolution (network, Internet)

Conversion of a network-layer address (e.g. IP address) into the corresponding physical address (e.g., MAC address).

ADM

Add-Drop Multiplexing/Multiplexer (network, ATM)
US term for a drop-and-insert multiplexing. Terminology for the removal (drop) or insertion (add) of traffic at some intermediate point on an end-to-end transmission path.

Adaptive Differential/Delta Modulation (network)
An example of waveform coding voice compression algorithm.

ADPCM

Adaptative Differential Pulse Code Modulation
A ITU-TS standard technique for voice encoding and compression. It allows an analog to be carried within a 32Kbit/s digital channel.

ADSL

Asymmetric Digital Subscriber Line (communications, protocol, network)
Copper pair technology, a variation of Digital Subscriber LineDigital Subscriber Line designed for an upstream data flow (client-to-server) which is a fraction of the downstream data flow (server-to-client). Typically the upstream data flow is measured in kilobits per second while the downstream data flow is measured in megabits per second (e.g. 6 megabits per second over standard phone lines).
ADSL is appropriate for applications such as Video on Demand or World-Wide Web where a request from the user is far less data than the response.
Like ISDN, ADSL uses standard phone lines to deliver high-speed data communications. But while ISDN's transmission speed is limited to 64 kbps, ADSL technology can deliver upstream (from the user) speeds of 640 kbps and downstream (to the user) speeds of more than 6 mbps. Even better, ADSL uses the portion of a phone line's bandwidth not utilized by voice, allowing for simultaneous voice and data transmission. However, as of late 1996, ADSL was still in development and not widely available.
The ECSA/ANSI subworking group T1E1.4 is recommending Discrete Multi-Tone (DMT) modulation as the standard over QAM or CAP modulations. See also ISDN, ADSL Forum home page, ADSL Forum tutorial.

AFA

Association des Fournisseurs d'Accès (Internet, France)
French ISP lobby.

AFCEE

Association Française pour le Commerce et les Echanges Electroniques (lobby)
French organisation on "Electronic Interchanges and trade".
site: http://www.afcee.asso.fr/.

AFI

Authority and Format Identifier (ATM)
First byte of the ATM address that determines the address type. AFI 39 is DCC, 47 is ICD, and 45 indicates an E.164 format.

AFNOR

Association Française de Normalisation (standard)
A French technology standards organization. French member of the ISO organisation.

AFPI (network, Internet)

French organization of Internet Service providers.

AFUTT

Association Française des Utilisateurs du Téléphone et des Télécommunications (telecommunication, France)
French organization of french telecomunications consumers.

Agent

In a client-server model, the agent performs information preparation and exchange on behalf of a client or server application.

AHFG

ATM-Attached Host Fonctional Group (ATM)
The group of functions performed by a station that supports the ATM Forum's Multiprotocol Over ATM (MPOA) spec.

AIFF

Apple Audio Interchange File Format
Audio format used in the Macintosh and Unix (especially SGI) worlds.

AIM

ATM Inverse Multiplexer(ATM)
A term discontinued because of conflict with an established product. Refer to AIMUX.

AIMUX

ATM Inverse Multiplexing (network, ATM)
A device that allows multiple T1 or E1 communications facilities to be combined into a single broadband facility for the transmission of ATM cells.

Algorithm (programming)

A process or detailed sequence of actions necessary for a computer or intelligent device to perform a task, such as voice compression. Named after an Iranian mathematician, Al-Khawarizmi.

Alias

A name, usually short and easy to remember, that is translated into another name, usually long and difficult to remember.
Name for shortcuts in the Macintosh world.

AIR

Additive Cell Rate (ATM)
The cell rate a source can transmit after increasing its rate by the RIF.

AIS

Alarm Indication Signal (ATM, UNI Fault Management)
One of the OAM function types used for fault management (see also CC , RDI). all 1's, also called Blue Alarm. Used as a keep alive signal.

AIW

APPNImplementors Workshop (standard, body)
Vendor consortium standard Organisation on networking standards.
Focus: APPN and SNA. Membership: March 1997 : 45 vendors and consultants.

<B>AL

Access Link (network)

ALign (ATM)
8-bit field of the CPCS trailer of the AAL3/4 cell. It is used to complete the trailer to 32 bits.

Alternate Buffer (network)

A section of memory reserved for receipt of data after the primary buffer is full.

AMI

Alternate Mark Inversion (network)
The signal used on T1 lines that transmits consecutive one-bits by inverting the polarity of each bit. Zeros are represented by time, not voltage.

ATM Management Interface (ATM)

AMRF

See FDMA.

AMRT

See TDMA.

A/N

French equivalent of A/D (Analog/Digital)

Analog Signal (physical layer)

An electronic signal that varies in a continuous wave-like pattern that is "analogous" to human speech.

Anneau à jeton (réseau)

See Token Ring.

Anonymous FTP (network, Internet)

Anonymous FTP allows a user to retrieve documents, files, programs, and other archived data from anywhere in the Internet without having to establish a userid and password. By using the special userid of "anonymous" the network user will bypass local security checks and will have access to publicly accessible files on the remote system.
See also archive site, File Transfer Protocol, World Wide Web.

ANSI

American National Standards Institute (standard)
This organization is responsible for approving U.S. standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards (e.g., ANSI C is the version of the C language approved by ANSI). ANSI is a member of ISO. Membership (March 1997): 1,400 companies, organizations, government agencies and institutions.
A list of ANSI standards.
ANSI site: http://www.ansi.org/.

AOST

Association des Opérateurs de Services de Télécommunications (telecommunication, France)
French organization of french telcos.

APCM

Adaptative Pulse Code Modulation (physical layer, network)

API

Application Programming Interface
A set of functions used by an application program as a means for providing access to a system's (i.e.operating, communications) capabilities.

APP

APplication Program

APPC

Advanced Program to Program Communication (network)
In the IBM's SNA environment, communication method used to make applications communicate together without any hierarchy notion.

Applet (JAVA, web) (Internet)

A mini Java program that can be embedded in an HTML page.
Applets offer robustness and security functions. Applets (compared to Java applications) are not allowed to access certain resources on the local computer, such as files and serial devices (modems, printers, etc.), and are prohibited from communicating with most other computers across a network. The current rule is that an applet can only make an Internet connection to the computer from which the applet was sent(often called applet server). An applet gives to an html page dynamic functions.

AppleTalk (network)

A networking protocol developed by Apple Computer for communication between Apple Computer products and other computers. This protocol is independent of the network layer on which it is run. Current implementations exist for Localtalk, a 235Kb/s local area network; and Ethertalk, a 10Mb/s local area network.

Application Layer (network, OSI)

The top layer of the OSI Reference Model; implemented by various network applications, including e-mail, file transfer and terminal emulation. The application layer is concerned with the semantics of work (e.g. formatting electronic mail messages). How to represent that data and how to reach the foreign node are issues for lower layers of the network.

APPN

Advanced Peer-to-Peer Networking (network)
IBM network architecture for building dynamic routing across arbitrary network topologies. Intended as an eventual replacement for SNA, IBM's static routed, hierarchical network architecture.

APS

Automatic Protoection Switching (switch, network)

Archie (tool, networking, Internet)

A system to automatically gather, index and serve information on the Internet. The initial implementation of archie by McGill University School of Computer Science provided an indexed directory of filenames from all anonymous FTP archives on the Internet. Later versions provide other collections of information. See also archive site, Gopher, Prospero, Wide Area Information Servers.

Archive Site (Or "FTP site", "FTP archive") (networking)

An Internet host where program source, documents, e-mail or news messages are stored for public access via anonymous FTP, Gopher, World-Wide Web or other document distribution system. There may be several archive sites for e.g. a Usenet newsgroup though one may be recognised as the main one.
Some well-known archive sites include Imperial College, UK, UUNET, USA.
See also archie, GNU archive site, mirror.

Area - zone (ATM)

Part of a standard ATM Address that identifies a unique area within a Routing Domain.

ARP

Address Resolution Protocol (network, Internet)
The procedures and messages in any communications protocol which resolve local addresses to those of the network. In TCP/IP, the protocols for translating between IP addresses and physical addresses.

ARPA (network, Internet)

Advanced Research Projects Agency
An agency of the U.S. Department of Defense responsible for the development of new technology for use by the military. ARPA (formerly known as DARPA, nee ARPA) was responsible for funding much of the development of the Internet we know today, including the Berkeley version of Unix and TCP/IP.

ARPANET (network, Internet)

Advanced Research Projects Agency Network
A pioneering longhaul network funded by ARPA. Now retired, it served as the basis for early networking research as well as a central backbone during the development of the Internet.The ARPANET consisted of individual packet switching computers interconnected by leased lines. See also: Advanced Research Project Agency.

Arpenteur

French synonym of browser.

ART

Autorité de Régulation des Télécommunications (telecommunication, France)
French regulation organization on telecommunications.

AS

Autonomous Systems (network)
Part of the internet layer that routers use to relate to network connectivity and packet addressing; the router checks the network address and only routes on the host address if the source and destination are on the same network.

ASCII

American Standard Code for Information Interchange
a 7-bit binary code for use by PCs and some mainframes to represent alphanumeric and graphical characters. One bit is added to create an 8-bit character byte.

ASIC

Application-Specific Integrated Circuit (hardware)

ASN1

Abstract Syntax Notation 1 (standard, ISO)
The language used by the OSI protocols for describing abstract syntax.
This language is also used to encode SNMP packets. See also: Basic Encoding Rules.

Assigned Numbers (network, Internet)

The RFC [STD2] which documents the currently assigned values from several series of numbers used in network protocol implementations. This RFC is updated periodically and, in any case, current information can be obtained from the Internet Assigned Numbers Authority (IANA).
If you are developing a protocol or application that will require the use of a link, socket, port, protocol, etc., please contact the IANA to receive a number assignment.

Asynchronous (physical layer, network)

Signals that are sourced from independent clocks. These signals generally have no relation to each other and so have different frequencies and phase relationships.

ATC

ATM Transfert Capability (ATM)

ATDM (network)

Asynchronous Time-Division Multiplexing
An asynchronous and intelligent TDM where time slots are allocated to the users on demand (dynamically).

ATM

Asynchronous Transfert Mode (ATM)
A high-speed, connection-oriented switching and multiplexing technology that uses 53-byte cells (5-byte header, 48-byte payload)to transmit different types of traffic simultaneously, including voice, video, and data. It is asynchronous in that information streams can be sent independently without a common clock.

ATM can be described logically in three planes: The userplane coordinates the interface between user protocols, such as IP or SMDS (Switched Multimegabit Data Service) and ATM; themanagement plane coordinates the layers of the ATM stack; thecontrol plane coordinates signaling and setting up and tearing down virtual circuits.

ATM Address (ATM)

A 21-byte address that uniquely identifies an ATM endpoint. Three formats are specified in UNI 3.0: DCC, ICD, and E.164.

ATM API

ATM Application Program Interface (ATM)
Although several vendors have written proprietary code, no standard ATM API yet exists. The ATM forum is working on an API that will let application developers take advantage of ATM's quality of serviceand traffic management features; some forum members are pushing for a single API that supports other network interfaces when ATM is not available.

ATM CSU - ATM DSU

ATM channel/data service unit (ATM)
A device that converts information bits (i.e. transmitted over the telephony network) or frame-based information into (or from) a stream of ATM cells (seeCSU, DSU. Segments ATM-compatible information, such as DXI (data exchange interface) frames generated by a router, into ATM cells and then reassembles them at their destination.

ATM Forum (ATM, standard)

The primary organization developing and defining ATM standards. Principal members participate in committees and vote on specifications; auditing members cannot participate in committees but receive technical and marketing documentation; user members participate only in end-user roundtables.
Formed in 1991 by Adaptive Corp. (Redwood City, Calif.),Cisco Systems Inc. (San Jose, Calif.), Northern Telecom Ltd. (Mississauga, Ontario),and Sprint Corp. (Kansas City, Mo.),the ATM forum currently consists of 880 members (March 1997), 280 primary and 600 auditing, including manufacturers, carriers, end-users,and other interested parties. The user input is the End-User Network Rountable (ENR) with 155 user companies. URL: http://www.atmforum.com/.

ATM Layer (ATM)

The second layer of the ATM protocol stack that handles most of the processing and routing activities. These include building the ATM header, cell multiplexing/demultiplexing,cell reception and header validation, cell routing using VPIs/VCIs, payload-type identification, quality of service specification, Usage Parameter Control ( UPC) and flow control and prioritization.

ATM MIB(ATM)

IETF-defined Management Information Base (MIB) for managing VP/VC links and ATM PVC-supported services and interfaces.

ATM Pilot (ATM)

European experiment on ATM network.

ATM-SAP

ATM-Service Access Point (ATM)
The physical interface at the boundary between the AAL and the ATM layer. See also SAP, PHY-SAP.

Audiotex (communications, telephone)

A term used to identify an emerging industry that enables telephone end users to receive a variety of telephone-based information and entertainment services.
Access of voice based data across the telephone network. Refers to systems that play back information to callers. Information can be pre-recorded or it can be looked up in a database. Systems may be passive (person can not control the information played back) or interactive (see IVR). A database-access system in which users employ touch-tone telephones to access electronically stored and delivered libraries of short audio messages. Commonly referred to as Audiotext; a basic term for interactive voice response (IVR) services. A way to describe "Push 1 for tech support and 2 for sales."

AUI

Attachment Unit Interface Cable (network, Ethernet)
An IEEE 802.3 cable connecting the MAU (Media Access Unit) to a networked device; AUI also may refer to the host backpanel connector to which an AUI cable attaches.

AUP

Acceptable Use Policy (network)
Many transit networks have policies which restrict the use to which the network may be put.
For example, some networks may only be used for non-commercial purposes. Some AUPs limit the type of material which can be made available to the public (e.g., pornographic material). Enforcement of AUPs varies with the network. See also netiquette.

Authentication (general, security)

A security verification of the identity of a person or process.

Autoswitch (network)

See switch, PBX.

AS

Autonomous System (network)
A collection of routers under a single administrative authority using a common Interior Gateway Protocol for routing packets.

AUU

ATM User to User indication (ATM)
Less significant bit of the PTI field. Bit used in a particular way by the AAL5 layer to indicate the last cell of a message.

AVI (file format)

File format for animations.

Average Cell Rate (ATM)

The mean number of cells that the source can inject into a network over a given virtual connection (VC).

Average Cell Transfer Delay

The arithmetic average of a number of cell transfer delays (CTD). See also mean cell transfer delay.

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