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Glossary Section "A" ( Definitions )

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0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

abstract syntax A description of a data structure that is (Adaptation Layer). Protocol used on top of ATM to support higher layer service requirements. For data communications services, the AAL defines a segmentation reassembly protocol for mapping large data packets into the 48 octet information field of the ATM cell.

AAR Automatic Alternate Routing; failure recovery

AB signaling A technique for carrying telephony signaling information across T1 spans. In A & B signaling, the least significant bit from each channel in the 6th and 12 frames is robbed to pass signaling information. Bits from the 6th frame are the A bits, while the B bits are in the 12th frame.

ABR Available Bit Rate. An ATM service type in which the ATM network makes a "best effort" to meet the transmitter’s bandwidth requirements. ABR differs from other "best effort" service types by employing a congestion feedback mechanism that the ATM network uses to notify the transmitters that they should reduce their rate of data transmission until the congestion situation ceases. Thus, ABR does offer qualitative guarantee that the transmitter’s data should get to the intended receivers without experiencing unwanted cell loss.

A-bis GSM term for an interface linking between the BTS (base transceiver station) and the BSC (bas stattion controller).

ABCD signaling A logical expansion of AB signaling. ABCD signaling is used in ESF framing. Bits are robbed from frames 6,12,18 and 24.

AC Alternating Current

ACAMI Alternat Channel Alternate Mark Inversion. A method of enable Clear Channel capability while running Fractional T1 in areas where B8ZS is not available. ACAMI does this by filling even numbered time slots with a special fill pattern that contains seven ones. Customer data is transmitted in the odd numbered slots. therefore, the average Ones Density is sufficient to ensure that the T1 line staYs in sync.

ACARS Aircraft Communications and Reporting System, VHF network to extend ADNS.

ACCTS Aviation Coordinating Committee for Telecommunications Services, part of ARINC.

ACF Access Control Field, first byte in ATM header, similar to SAP.

ACF Access Coordination Function; tariffed service where AT&T obtains local loops between customer premises and AT&T serving office.

ACF Advanced Cummunications Function, SNA software.

ACK (Acknowledgment) A type of message sent to indicate that a block of data arrived at its destination without error. A negative acknowledgment is called a "NAK."

ACL Access Control List; 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 Association for Computer Machinery

ActiveX Microsoft’s Windows-specific non-Java technique for writing applets. ActiveX applets take considerably longer to download than the equivalent Java applets, however, they more fully exploit the features of Windows 95. ActiveX is sometimes said to be a "superset of Java."

A/D Analog to Digital, usually a conversion of voice to digital format.

AD Administrative Domain: A group of hosts, routers, and networks operated and managed by a single organization. This Internet concept is defined in RFC 1136.

address A coded representation of the origin or destination of data.

address resolution A means for mapping Network Layer addresses onto media-specific addresses.

address mask A bit mask used to select bits from an Internet address for subnet addressing. The mask is 32 bits long and selects the network portion of the Internet address and one or more bits of the local portion. Sometimes called sub-net mask.

ADMD Administration Management Domain. An X.400 Message Handling System public carrier. Examples: MCImail and ATTmail in the U.S., British Telecom's Gold400mail in the U.K. The AIMDs in all countries worldwide together provide the X.400 backbone. See PRMD.

ADNS ARINC Data Network Service, a packet network.

ADPCM Adaptive Differential Pulse Code Modulation, a form of voice compression that typically uses 32 kbit/s for digitizing a voice or analog signal.

ADSL Asymmetrical Digital Subscriber Line

AEP AppleTalk Echo Protocol. Allows a node on an AppleTalk network to send a packet to another node and in return, receive an echoed copy of the packet.

AFI Authority and Format Identifier, part of network level address header (MAP).

AFP AppleTalk filing Protocol. Protocol that allows distributed file sharing across an AppleTalk network.

agent In the client-server model, the part of the system that performs information preparation and exchange on behalf of a client or server application. In SNMP, the word agent refers to the managed system.

AIS Alarm Indicating signal. another name for a Blue Alarm.

ALG Application Layer Gateway

Alpha Alpha testing is the first step in testing new software or hardware.

AMI Alternate Mark Inversion A bipolar coding which uses successive ones (marks) must alternate in polarity.

Analog A continuous wave or signal (such as a human voice)

Analog Loopback A testing technique that isolates faults in transmission equipment by performing a loopback on the data at the analog (line) side of the modem.

Analog Transmission The transmission of a continuous variable signal

Anonymous FTP Allows a user to retrieve documents, files, programs, and other archived data from anywhere in 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. See FTP.

Answer Supervision A signaling on telephone lines generally used for the billing purposes. Basically, a signal is sent back to the originating central office (CO) that tells that office that the call has been answered.

ANSI American National Standards Institute

ASN.l Abstract Syntax Notation One. The OSI language for describing abstract syntax. Often called "Asenine One" by Internet cynics. 

AO/DI Always On / Dynamic ISDN

AOW Asia and Oceania Workshop. One of the three regional OSI Implementors Workshops.

AP Access Point. A device which allows for a wireless  to a network.

APC Angled Polished Connector

APL Analog Private Line. A line leased from a carrier, APL is the type of line on which you would operate a leased line modem.

APNIC Asia Pacific Network Information Center. A Non-profit Internet Registry Organization for The Asia Pacific Region. The other Internet Registries are currently LANA, RIPE NCC and InterNIC.

APPC Advanced Program-to-Program Communications. Part of IBM's Systems Network Architecture (SNA).

applet A small program, often used in the context of a Java-based program, that is compiled and embedded in an HTML page.

AppleTalk A networking protocol developed by Apple Computer for communication between Apple Computer products and other computers. This protocol is independent of what network it is layered on. Current implementations exist for LocalTalk (235Kbps) and EtherTalk (10Mbps).

application A program that performs a function directly for a user. FTP, mail and Telnet clients are examples of network applications.

Application Layer The top layer of the network protocol stack. 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.

APS Automatic Protection Switching

Archie A system which provides lists of anonymous FTP archives. See Gopher, Prospero, WAIS, World-Wide Web.

ARCNET Attached Resource Computer Network was one of the earliest Local Area Networks. It uses a Toke Passing scheme at 2.5 Mbps in both star and bus topologies.

ARD Automatic Ring Down: lifting your phone rings the far end without dialing.

ARIN American Registry for Internet Numbers. A non-profit organization established for the purpose of administration and registration of Internet Protocol (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.

ARP Address Resolution Protocol. The Internet protocol used to dynamically map Internet addresses to physical (hardware) addresses on local area networks. Limited to networks that support hardware broadcast.

ARPA Advanced Research Projects Agency. Now called DARPA (Defense Advanced Research Projects Agency), the U.S. government agency that funded the ARPANET.

ARPANET A packet switched network developed in the early 1970s. The "grandfather" of today's Internet. ARPANET was decommissioned in June 1990.

ARQ Automatic Request for Retransmission

ASCII American Standard Code for Information Interchange. As a 7-level code it can generate 128 different characters. An eighth bit can be used for parity.

ASDS Accunet Spectrum of Digital Services.

Assigned Numbers The RFC ISTD2] 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 (LANA). If you are developing a protocol or application that will require the use of a link, socket, port, protocol, etc., please contact the LANA to receive a number assignment.

Asynchronous A mode where characters travel individually down the line as they are keyed.

Asynchronous Transmission A transmission method that sends units of data on character at a time. Characters are proceeded by start bits and followed by stop bits,  which provide synchronization at the receiving device

ATC Adaptive Transform Coding. A method used to encode voice transmissions using only 16 kbps.

ATM Asynchronous Transfer Mode. The SONET standard for a packet switching technique which uses packets (cells) of a fixed length. Also referred to as BISDN and Cell Relay.

Attenuation Signal power loss through equipment, lines or other devices.

attribute The form of information items provided by the X.500 Directory Service. The directory information base consists of entries, each containing one or more attributes. Each attribute consists of a type identifier together with one or more values.

AUI  stands for Attachment Unit Interface. It is a connector that typically attaches Ethernet equipment such as a workstation or fan-out box to a transceiver.

AUP Acceptable Use Policy. Many transit networks have policies which restrict the use to which the network may be put. A well known example is NSFNET's AUP which did not allow for commercial use. Enforcement of AUPs varies with the network.

authentication In security, the verification of the identity of a person or process.

Autonomous System (AS) Internet (TCP/IP) terminology for a collection of gateways (routers) that fall under one administrative entity and cooperate using a common Interior Gateway Protocol (IGP). See subnetwork.

AWG The American Wire Gauge System, which specifies wire width.

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