Section 2 A Terms Flashcards
A&B bit signaling
Procedure used in 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.
AAL
ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers, CS and SAR, AALs differ on the basis of the source-destination timing used, whether they use DBR or VBR, and whether they are used for connection-oriented or connectionless mode data transfer. At present, the four types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5.
AAL1
ATM adaptation layer 1. One of four AALs recommended by the ITU-T. AAL1 is used for connection-oriented, delay-sensitive services requiring constant bit rates, such as uncompressed video and other isochronous traffic.
AAL2
ATM adaptation layer 2. One of four AALs recommended by the ITU-T. AAL2 is used for connection-oriented services that support a variable bit rate, such as some isochronous video and voice traffic.
AAL3/4
ATM adaptation layer 3/4. One of four AALs (merger from two initially distinct adaptation layers) recommended by the ITU-T. AAL 3/4 supports both connectionless and connection oriented links, but is primarily used for the transmission of SMDS packets over ATM networks.
AAL5
ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented, VBR services, and is used predominantly for the transfer of classic IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth over head and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.
AARP
AppleTalk Address Resolution Protocol. Protocol in the AppleTalk protocol stack that maps a data-link address to a network address.
AARP probe packets
Packets transmitted by AARP that determine whether a randomly selected node ID is being used by another node in a nonextended AppleTalk network. If the node ID is not being used, the sending node uses that node ID. If the node ID is being used, the sending node chooses a different ID and sends more AARP probe packets.
ABM
Asynchronous Balanced Mode. An HDLC (and derivative protocol) communication mode supporting peer-oriented, point-to- point communications between two stations, where either station can initiate transmission.
ABR
- 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 delays, providing only best-effort service. Traffic sources adjust their transmission rate in response to information they receive describing the statue of the network and its capability to successfully deliver data. Compare with CBR, UBR, and VBR. 2. 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.
AC
Alternating Current. An electrical power transmission system in which the direction of current flow alternates on a periodic basis.
Accelerator
A hardware addition to an existing computing device that increases the computer’s processing speed and capabilities.
Access
Referring to the ability of a computing device to use data or resources beyond its native capabilities.
Access List
List kept by routers to control access to or from the router for a number of services. For example, the list can prevent packets with a certain IP address from leaving a particular interface on the router.
Access Method
The type of Media Access Control method that a node uses to gain control of a network.
Accounting
One of five categories of network management defined by ISO for
Management
management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage. See also configuration management, fault management, performance management, and security management.
Accuracy
Referring to how closely a test instrument’s measurements compare to a standard value, usually expressed as a percentage of the value measured.
ACF
Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing.
ACF/NCP
Advanced Communications Function/Network Control Program. The primary SNA NCP. ACF/NCP resides in the communications controller and interfaces with the SNA access method in the host processor to control network communications.
Acknowledgment
Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) has occurred. Sometimes abbreviated ACK.
ACR
Allows 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.
ACSE
Association control service element. An OSI convention used to establish, maintain or terminate a connection between two applications.
Active Hub
Multiported device that amplifies LAN transmission signals.
Active Monitor
Device responsible for managing a Token Ring. A network node is selected to be the active monitor if it has the highest MAC address on the ring. The active monitor is responsible for management tasks such as ensuring that tokens are not lost or that frames do not circulate indefinitely.
Adapter
Hardware that allows a computing device physical access to a network.
Adaptive Routing
See dynamic routing.
ADCCP
Advanced Data Communications Control Protocol.
Address
A numerical designation that uniquely refers to a specific communication entity.
Addressed Call
Mode that permits control signals and commands to Mode
Addressed Call Mode
Mode that permits control signals and commands to
ACM to establish and terminate calls in V.25bis.
Address Mapping
Technique that allows different protocols to interoperate by translating addresses from one format to another. For example, when routing IP over X.25, the IP addresses must be mapped to the X.25 addresses so that the IP packets can be transmitted by the X.25 network. See also address resolution.
Address Mask
Bit combination used to describe which portion of anaddress refers to the network or subnet and which partrefers to the host. Sometimes referred to simply as mask.also subnet mask.
Address Resolution
When two addressing systems refer to the same entity, the process of translating or expressing the address of an entity on one system to the equivalent address of the same entity in the second system. For instance, translating an IP address to its given DNS name.
Address Space
The range of possible unique addresses allowed by an addressing scheme.
Adjacency
Relationship formed between selected neighboring routers and end nodes for the propose of exchanging routing information. Adjacency is based upon the use of a common media segment.
Adjacent Nodes
- In SNA, nodes that are connected to a given node with no intervening nodes. 2. In DECnet and OSI, nodes that share a common network segment (in Ethernet, FDDI, or Token Ring networks).
Administrative Distance
A rate of the trustworthiness of a routing information source. The higher the value, the lower the trustworthiness rating.
ADPCM
Adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals.
ADSU
ATM DSU. Terminal adapter used to access an ATM network via an HSSI-compatible device. See also DSU.
Advertising
Router process in which routing or service updates are sent at specified intervals so that other routers on the network can maintain lists of usable routes.
AEP
AppleTalk Echo Protocol. Used to test connectivity between two AppleTalk nodes. One node sends a packet to another node and receives a duplicate, or echo, of that packet.
AFP
AppleTalk Filing Protocol. The Apple proprietary specification for a network file system.
Agent
- An active process in a computer that is responsible for a certain type of activity when demanded by an outside entity. 2. In SNMP, the active process in a computing device that is responsible for determining the parameters defined in the MIB (Management Information Base) and reporting them on demand to a Console.
AIS
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.
AIX
IBM’s implementation of Unix.
Alarm
Message notifying an operator or administrator of a network problem. See also event and trap.
A-law
The ITU-T companding standard used in the conversion between analog and digital signals in PCM systems. A-law is used primarily in European telephone networks and is similar to the North American mu-law standard. See also companding and mu-law.
Algorithm
A set of rules and decision structures for actions in a specifically defined set of circumstances.
Alias
A file whose sole purpose is to represent another file.
Alignment Error
In IEEE 802.3 networks, an error that occurs when the total number of bits of a received frame is not divisible by eight. Alignment errors are usually caused by frame damage due to collisions.
All-rings/routes Explorer Packet
packet that traverses an entire SRB network, following all possible paths to a specific destination. Sometimes called all-rings explorer packet, See also explorer packet, local explorer packet, and spanning explorer packet.
ALOE
Archaic. AppleTalk Low Overhead Encapsulation. A vendor-developed alternative to AURP, ALOE provides a mechanism to tunnel AppleTalk protocols inside IP packets, typically in WAN links.
Alphanumeric
Referring to a group of printable characters that includes the letters of the alphabet in both upper and lower case, the numerals plus a limited group of additional symbols and punctuation marks.
AM
Amplitude Modulation. Modulation technique whereby information is conveyed through the amplitude of the carrier signal. Compare with FM and PAM. See also modulation.
Ambient
Referring to a set of conditions that exist independently of the system of interest.
AMI
Alternate 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 device maintain ones density. Ones density is not maintained independent of the data stream. Sometimes called binary coded alternate mark inversion. See also ones density.
Amp
Ampere. A standard unit of measurement for electrical current flow.
Amplitude
In the terminology of wave motion, the height of the wave. Amplitude is usually measured from a reference point of 0. In electrical waves, amplitude is typically expressed in volts.
Analog
Referring to a system or component that uses a system of measurement, response or storage in which values are expressed a s a magnitude using a continuous scale of measurement.
Analog Transmission
Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency, and phase.
Anomaly
An unusual instance or circumstance.
ANSI
American National Standards Institute. The principle group in the US. for defining standards.
AOCE
Apple Open Collaboration Environment. A system of higher- level protocols used for the transmission of data and authentication between applications.
APaRT
Automated packet recognition/translation. Technology that allows a server to be attached to CDDI or FDDI without requiring the reconfiguration of applications or network protocols. APaRT recognizes specific data link layer encapsulation packet types and, when these packet types are transferred from one medium to another, translates them into the native format of the destination device.
API
Application Programming Interface. A set of tools and procedures provided by the programmer of an application so that other programmers can control, exchange data with, or extend the functionality of an application.
Apollo Domain
Proprietary network protocol suite developed by Apollo Computer for communication on proprietary Apollo networks.
APPC
Advanced Program-to-Program Communication. IBM SNA system software that allows high-speed communication between programs on different computers in a distributed computing environment. APPC establishes and tears down connections between communicating programs, and consists of two interfaces, a programming interface and a data-exchange interface. The former replies to requests from programs requiring communication; the latter establishes sessions between programs. APPC runs on LU 6.2 devices. See also LU 6.2.
AppleEvent
Apple’s primary mechanism for interprocess communication.
AppleScript
A programming language that can call tasks within Macintosh applications.
AppleShare
An application published by Apple that allows a Macintosh to be a file server using the AFP protocol.
AppleTalk
- Apple’s proprietary network architecture. 2. The protocols, applications, networks and services included in Apple’s network architecture.
Application
An independently executable set of algorithms and data structures that perform a specific set of functions.
Application Layer
Layer 7 of the OSI reference model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and agreement on procedures for error recovery and control of data integrity. Corresponds roughly with the transaction services layer in the SNA model. See also data link layer, network layer, physical layer, presentation layer, session layer, and transport layer.
APPN
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. Compare with APPN+. See also APPC.
APPN+
Next-generation APPN that replaces the label-swapping routing algorithm with source routing. Also called high-performance routing. See also APPN.
ARA
AppleTalk Remote Access. Protocol that provides Macintosh users direct access to information and resources at a remote AppleTalk site.
Architecture
The sum total of all of the specifications, protocols and implementations that define a particular networking system.
Archive
A storage of infrequently-used or historical data.
ARCnet
Attached Resource Computer Network. A 2.5-Mbps token-bus LAN developed in the late 1970s and early 1980s by Datapoint Corporation.
Area
Logical set of network segments (either CLNS-, DECnet-, OSPF-based) and their attached devices. Areas are usually connected to other areas via routers, making up a single autonomous system. See also autonomous system.
ARM
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. See also primary station and secondary station.
ARP
Address Resolution Protocol. The protocol for mapping IP addresses to physical addresses such as Ethernet or Token Ring.
ARPA
Advanced Research Projects Agency, Research and development organization that is part of DoD. ARPA is responsible for numerous technological advances in communications and networking. ARPA evolved in DARPA, and then back into ARPA again (in 1994). See also DARPA.
ARPANET
Advanced Research Projects Agency Network. Landmark packet-switching network established in 1969. ARPANET was developed in the 1970s by BBN and funded by ARPA (and later DARPA). It eventually evolved into the Internet. The term ARPANET was officially retired in 1990.
ARQ
Automatic repeat request. Communication technique in which the receiving device detects errors and requests retransmission.
ASBR
Autonomous system boundary router. ABR located between an OSPF autonomous system and a non-OSPF network. ASBRs run both OSPF and another routing protocol, such as RIP, ASBRs must reside on a nonstub OSPF area.
ASCII
Referring to a standard 7-bit character system that includes the alphanumeric characters and printer control codes.
ASDSP
AppleTalk Secure Data Stream Protocol. An encrypted version of ADSP used by AOCE.
ASIC
Application-Specific Integrated Circuit. A custom chip for a specific application.
ASLM
Apple Shared Library Manager.
ASN.1
Abstract Syntax Notation One. In SNMP, the language used to describe data managed by the MIB.
Associative Memory
Memory that is accessed based on its contents, not on its memory address. Sometimes called content addressable memory (CAM).
AST
Automatic spanning tree. Function that supports the automatic resolution of spanning trees in SRB networks, providing a single path for spanning explorer frames to traverse from a given node in the network to another. AST is based on the IEEE 802.1 standard.
ASTA
Advanced Software Technology and Algorithms. Component of the HPCC program intended to develop software and algorithms for implementation on high-performance computer and communications systems. See also HPCC.
Asymmetry
In networking, a system in which the relationship between two entities is inherently unequal, with each entity restricted to a set of operations and prerogatives defined by its role in the relationship.
Asynchronous
A system of communication in which each discreet delivery of information establishes its own timing impulse rather than having to conform to the timing impulse of previous deliveries.
Asynchronous
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. Compare with Isochronous transmission, plesiochronous transmission, and synchronous transmission.
AT commands Transmission
A set of commands that control a modem or alter its characteristics.
ATDM
Asynchronous time-division multiplexing. Method of sending information that resembles normal TDM, except that time slots are allocated as needed rather than preassigned to specific transmitters. Compare with FDM, Statistical multiplexing, and TDM.
ATM
Asynchronous Transfer Mode. A broadband transmission system using 53-octet packets over a cell-switched network at speeds up to 2.2 GBPS.
ATP
AppleTalk Transaction Protocol. Transport-level protocol that allows reliable request-response exchanges between two socket clients.
Attenuation
A loss in the amplitude or strength of a signal due to an interaction with the signal’s media. Generally expressed in decibels.
Attribute
Configuration data that defines the characteristics of database objects such as the chassis, cards, ports, or virtual circuits of a particular device. Attributes might be preset or user-configurable. On a LightStream 2020 ATM switch, attributes are set using the configuration program or CLI commands.
AUI
Attachment unit interface. IEEE 802.3 interface between an MAU and a NIC (network interface card). Also called transceiver cable.
AURP
AppleTalk Update-Based Routing Protocol. Apple’s WAN protocol.
AURP Tunnel
Connection created in an AURP WAN that functions as a single, virtual data link between AppleTalk internetworks physically separated by a foreign network (a TCP/IP network, for example).
Authority Zone
Associated with DNS, an authority zone is a section of the domain-name tree for which one name server is the authority.
Automatic Call Reconnect
Feature permitting automatic call rerouting away from a failedtrunk line.
Autonomous Confederation
Group of autonomous systems that rely on their own networkreachability and routing information more than they rely on that received from other autonomous systems or confederations.
Autonomous System
Collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16-bit number by the IANA. Sometimes abbreviated AS.
Autoreconfiguration
Process performed by nodes within the failure domain of a Token Ring network. Nodes automatically perform diagnostics in an attempt to reconfigure the network around the failed areas.
Average Rate
The average rate, in kilobits per second (kbps), at which a given virtual circuit will transmit.
