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Advanced Communications
Function/Network Control Program
See ACF/NCP.
Advanced Data Communications
Control Protocol
See ADCCP.
Advanced Peer-to-Peer Networking See APPN.
Advanced Program-to-Program
Communication
See APPC.
Advanced Research Projects Agency See ARPA.
Advanced Research Projects Agency
Network
See ARPANET.
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
A
ppleTalk 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.
agent
1) Generally, software that processes queries and returns
replies on behalf of an application.
2) In NMSs, process that resides in all managed devices and
reports the values of specified variables to management
stations.
3) In Cisco hardware architecture, an individual processor card
that provides one or more media interfaces.
AGS+
Multiprotocol, high-end Cisco router optimized for large
corporate internetworks. The AGS+ runs the Cisco IOS
software and features a modular approach that provides for
easy and efficient scalability.
AIP
ATM Interface Processor. ATM network interface for Cisco
7000 series routers designed to minimize performance
bottlenecks at the UNI. The AIP supports AAL3/4 and AAL5.
See also AAL3/4, AAL5, and Cisco 7000.
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. See also T1.
alarm
Message notifying an operator or administrator of a network
problem. See also event and trap.
alarm indication signal See AIS.
A - 6 CCNA 1-4 v 3.0 – Glossary Copyright 2003, Cisco Systems, Inc.
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
Well-defined rule or process for arriving at a solution to a
problem. In networking, algorithms are commonly used to
determine the best route for traffic from a particular source to a
particular destination.
alias See entity.
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.
allowed cell rate See ACR.
all-rings explorer packet See all-routes explorer packet.
all-routes explorer packet
Explorer 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.
alternate mark inversion See AMI.
AM
amplitude modulation. Modulation technique whereby
information is conveyed through the amplitude of the carrier
signal. Compare with FM and PAM. See also modulation.
American National Standards Institute See ANSI.
American Standard Code for
Information Interchange
See ASCII.
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. Compare with B8ZS. See also ones density.
amplitude
Maximum value of an analog or a digital waveform.
amplitude modulation See AM.
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.
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ANSI
American National Standards Institute. Voluntary organization
comprised of corporate, government, and other members that
coordinates standards-related activities, approves U.S. national
standards, and develops positions for the United States in
international standards organizations. ANSI helps develop
international and U.S. standards relating to, among other
things, communications and networking. ANSI is a member of
the IEC and the ISO. See also IEC and ISO.
ANSI X3T9.5 See X3T9.5.
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. Specification of function-call
conventions that defines an interface to a service.
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.
AppleTalk
Series of communications protocols designed by Apple
Computer. Two phases currently exist. Phase 1, the earlier
version, supports a single physical network that can have only
one network number and be in one zone. Phase 2, the more
recent version, supports multiple logical networks on a single
physical network and allows networks to be in more than one
zone. See also zone.
AppleTalk Address Resolution
Protocol
See AARP.
AppleTalk Echo Protocol See AEP.
AppleTalk Remote Access See ARA.
AppleTalk Transaction Protocol See ATP.
AppleTalk Update-Based Routing
Protocol
See AURP.
AppleTalk zone See zone.
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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 establishes 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.
application programming interface See API.
applique
Mounting plate, used primarily in the Cisco AGS+, MGS, and
CGS chassis, containing connector hardware allowing
attachment to the network. Appliques translate communication
signals from a network interface into the signals expected by
the communication standard being used (such as EIA/TIA-232
or V.35). See also fantail.
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.
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-, or
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.
area border router See ABR.
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. Internet protocol used to map an
IP address to a MAC address. Defined in RFC 826. Compare
with RARP. See also proxy ARP.
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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 into 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. See also ARPA, BBN,
DARPA, and Internet.
ARQ
automatic repeat request. Communication technique in which
the receiving device detects errors and requests
retransmissions.
AS See autonomous system.
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 in a nonstub OSPF area. See also ABR,
non-stub area, and OSPF.
ASCII
American Standard Code for Information Interchange. 8-bit
code for character representation (7 bits plus parity).
ASM-CS
Cisco multiprotocol communication server designed to connect
asynchronous devices to any LAN or WAN using TCP/IP, LAT,
or SLIP. It can be configured to interface with Ethernet or Token
Ring LANs or synchronous serial networks.
ASN.1
Abstract Syntax Notation One. OSI language for describing
data types independent of particular computer structures and
representation techniques. Described by ISO International
Standard 8824. See also BER (basic encoding rules).
association control service element See ACSE.
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. See IEEE 802.1 and SRB.
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.
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Asynchronous Balanced Mode See ABM.
asynchronous response mode See ARM.
asynchronous time-division
multiplexing
See ATDM.
Asynchronous Transfer Mode See ATM.
asynchronous transmission
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.
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.
ATG
address translation gateway. Cisco DECnet routing software
function that allows a router to route multiple, independent
DECnet networks and to establish a user-specified address
translation for selected nodes between networks.
ATM
Asynchronous Transfer Mode. International standard for cell
relay in which multiple service types (such as voice, video, or
data) are conveyed in fixed-length (53-byte) cells. Fixed-length
cells allow cell processing to occur in hardware, thereby
reducing transit delays. ATM is designed to take advantage of
high-speed transmission media such as E3, SONET, and T3.
ATM adaptation layer See AAL.
ATM adaptation Layer 1 See AAL1.
ATM adaptation Layer 2 See AAL2.
ATM adaptation Layer 3/4 See AAL3/4.
ATM adaptation Layer 5 See AAL5.
ATM data service unit See ADSU.
ATM Forum
International organization jointly founded in 1991 by Cisco
Systems, NET/ADAPTIVE, Northern Telecom, and Sprint that
develops and promotes standards-based implementation
agreements for ATM technology. The ATM Forum expands on
official standards developed by ANSI and ITU-T, and develops
implementation agreements in advance of official standards.
ATM interface processor See AIP.
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ATM layer
Service-independent sublayer 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. See also AAL.
ATMM
ATM management. Process that runs on an ATM switch that
controls VCI translation and rate enforcement. See also ATM
and VCI.
ATM management See ATMM.
ATM UNI See UNI.
ATM user-user connection
Connection created by the ATM layer to provide communication
between two or more ATM service users, such as ATMM
processes. Such communication can be unidirectional, using
one VCC, or bidirectional, using two VCCs. See also ATM
layer, ATMM, and VCC.
ATP
AppleTalk Transaction Protocol. Transport-level protocol that
allows reliable request-response exchanges between two
socket clients.
Attached Resource Computer Network See ARCnet.
attachment unit interface See AUI.
attenuation
Loss of communication signal energy.
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). The term AUI can
also refer to the rear panel port to which an AUI cable might
attach, such as those found on a Cisco LightStream Ethernet
access card. Also called transceiver cable. See also IEEE
802.3, MAU, and NIC (network interface card).
AURP
AppleTalk Update-Based Routing Protocol. Method of
encapsulating AppleTalk traffic in the header of a foreign
protocol, allowing the connection of two or more discontiguous
AppleTalk internetworks through a foreign network (such as
TCP/IP) to form an AppleTalk WAN. This connection is called
an AURP tunnel. In addition to its encapsulation function,
A
URP maintains routing tables for the entire AppleTalk WAN by
exchanging routing information between exterior routers. See
also AURP tunnel and exterior router.
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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). See also AURP.
authority zone
Associated with DNS, an authority zone is a section of the
domain-name tree for which one name server is the authority.
See also DNS.
Automated Packet
Recognition/Translation
See APaRT.
automatic call reconnect
Feature permitting automatic call rerouting away from a failed
trunk line.
automatic repeat request See ARQ.
automatic spanning tree See AST.
autonomous confederation
Group of autonomous systems that rely on their own network
reachability and routing information more than they rely on that
received from other autonomous systems or confederations.
autonomous switching
Feature on Cisco routers that provides faster packet processing
by allowing the ciscoBus to switch packets independently
without interrupting the system processor.
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. See also area and IANA.
autonomous system boundary router See ASBR.
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. See also failure domain.
available bit rate See ABR.
average rate
The average rate, in kilobits per second (kbps), at which a
given virtual circuit will transmit.
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B
Term Definition
B8ZS
binary 8-zero substitution. Line-code type, used on T1 and E1
circuits, in which a special code is substituted whenever 8
consecutive zeros are sent through the link. This code is then
interpreted at the remote end of the connection. This technique
guarantees ones density independent of the data stream.
Sometimes called bipolar 8-zero substitution. Compare with
AMI. See also ones density.
backbone
The part of a network that acts as the primary path for traffic
that is most often sourced from, and destined for, other
networks.
backbone cabling
Cabling that provides interconnections between wiring closets,
wiring closets and the POP, and between buildings that are
part of the same LAN. See vertical cabling.
back end
Node or software program that provides services to a front
end. See also client, front end, and server.
backoff
The retransmission delay enforced when a collision occurs.
backplane
Physical connection between an interface processor or card
and the data buses and power distribution buses inside a
Cisco chassis.
back pressure
Propagation of network congestion information upstream
through an internetwork.
backward explicit congestion
notification
See BECN.
backward learning
Algorithmic process used for routing traffic that surmises
information by assuming symmetrical network conditions. For
example, if node A receives a packet from node B through
intermediate node C, the backward-learning routing algorithm
will assume that A can optimally reach B through C.
balanced configuration
In HDLC, a point-to-point network configuration with two
combined stations.
balanced, unbalanced See balun.
balun
balanced, unbalanced. Device used for matching impedance
between a balanced and an unbalanced line, usually twisted-
pair and coaxial cable.
bandwidth
The difference between the highest and lowest frequencies
available for network signals. The term is also used to describe
the rated throughput capacity of a given network medium or
protocol.
B - 14 CCNA 1-4 v 3.0 – Glossary Copyright 2003, Cisco Systems, Inc.
bandwidth allocation See bandwidth reservation.
bandwidth reservation
Process of assigning bandwidth to users and applications
served by a network. Involves ssigning priority to different flows
of traffic based on how critical and delay-sensitive they are.
This makes the best use of available bandwidth, and if the
network becomes congested, lower-priority traffic can be
dropped. Sometimes called bandwidth allocation. See also call
priority.
banner motd
Command used to configure a message of the day which is
displayed at login and is useful for conveying messages that
affect all network users, such as impending system shutdowns.
Banyan VINES See VINES.
BARRNet
Bay Area Regional Research Network. Regional network
serving the San Francisco Bay Area. The BARRNet backbone
is composed of four University of California campuses
(Berkeley, Davis, Santa Cruz, and San Francisco), Stanford
University, Lawrence Livermore National Laboratory, and
NASA Ames Research Center. BARRNET is now part of BBN
Planet. See also BBN Planet.
baseband
Characteristic of a network technology where only one carrier
frequency is used. Ethernet is an example of a baseband
network. Also called narrowband. Contrast with broadband.
bash
Bourne-again shell. Interactive UNIX shell based on the
traditional Bourne shell, but with increased functionality. The
LynxOS bash shell is presented when you log in to a
LightStream 2020 ATM switch as root (bash#) or fldsup
(bash$). See also fldsup account and root account.
basic configuration
The minimal configuration information entered when a new
router, switch, or other configurable network device is installed
on a network. The basic configuration for a LightStream 2020
ATM switch, for example, includes IP addresses, the date, and
parameters for at least one trunk line. The basic configuration
enables the device to receive a full configuration from the
NMS.
basic encoding rules See BER.
Basic Rate Interface See BRI.
Basic Research and Human Resources See BRHR.
baud
Unit of signaling speed equal to the number of discrete signal
elements transmitted per second. Baud is synonymous with
bits per second (bps), if each signal element represents exactly
1 bit.
Bay Area Regional Research Network See BARRNet.
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