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429 Cards in this Set

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10-Mbps baseband Ethernet specification using 50-ohm thin coaxial cable. 10Base2, which is part of the IEEE 802.3 specification, has a distance limit of 606.8 feet (185 meters) per segment. Also called Thinnet or Cheapernet


10-Mbps baseband Ethernet specification using standard (thick) 50-ohm baseband coaxial cable. 10Base5, which is part of the IEEE 802.3 baseband physical layer specification, has a distance limit of 1640 feet (500 meters) per segment.


10-Mbps baseband Ethernet specification that refers to the 10BaseFB, 10BaseFL, and 10BaseFP standards for Ethernet over fiber-optic cabling.


10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BaseFB is part of the IEEE 10BaseF specification. It is not used to connect user stations, but instead provides a synchronous signaling backbone that allows additional segments and repeaters to be connected to the network.


10-Mbps baseband Ethernet specification using fiber-optic cabling. 10BaseFL is part of the IEEE 10BaseF specification and, while able to interoperate with FOIRL, is designed to replace the FOIRL specification. 10BaseFL segments can be up to 3280 feet (1000 meters) long if used with FOIRL, and up to 1.24 miles (2000 meters) if 10BaseFL is used exclusively.


10-Mbps fiber-passive baseband Ethernet specification using fiber-optic cabling. 10BaseFP is part of the IEEE 10BaseF specification. It organizes a number of computers into a star topology without the use of repeaters. 10BaseFP segments can be up to 1640 feet (500 meters) long.


10-Mbps baseband Ethernet specification using two pairs of twisted-pair cabling (Category 3, 4, or 5): one pair for transmitting data and the other for receiving data. 10BaseT, which is part of the IEEE 802.3 specification, has a distance limit of approximately 328 feet (100 meters) per segment.


10-Mbps broadband Ethernet specification using broadband coaxial cable. 10Broad36, which is part of the IEEE 802.3 specification, has a distance limit of 2.24 miles (3600 meters) per segment.


100-Mbps baseband Fast Ethernet specification using two strands of multimode fiber-optic cable per link. To guarantee proper signal timing, a 100BaseFX link cannot exceed 1312 feet (400 meters) in length.


100-Mbps baseband Fast Ethernet specification using UTP wiring. Like the 10BaseT technology on which it is based, 100BaseT sends link pulses over the network segment when no traffic is present. However, these link pulses contain more information than those used in 10BaseT. Based on the IEEE 802.3 standard.


100-Mbps baseband Fast Ethernet specification using four pairs of Category 3, 4, or 5 UTP wiring. To guarantee proper signal timing, a 100BaseT4 segment cannot exceed 328 feet (100 meters) in length. Based on the IEEE 802.3 standard.


100-Mbps baseband Fast Ethernet specification using two pairs of either UTP or STP wiring. The first pair of wires is used to receive data; the second is used to transmit. To guarantee proper signal timing, a 100BaseTX segment cannot exceed 328 feet (100 meters) in length. Based on the IEEE 802.3 standard.


100-Mbps baseband Fast Ethernet specification that refers to the 100BaseFX and 100BaseTX standards for Fast Ethernet over fiber-optic cabling. Based on the IEEE 802.3 standard.


100-Mbps Fast Ethernet and Token Ring media technology using four pairs of Category 3, 4, or 5 UTP cabling. This high-speed transport technology, developed by Hewlett-Packard, can operate on existing 10BaseT Ethernet networks. Based on the IEEE 802.12 standard.


Historic term that refers to the original ARPANET host-to-IMP interface. The specifications are in BBN report 1822.


2 binary 1 quaternary. Encoding scheme that provides a 2 bits per baud, 80-kbaud per second, 160-kbps transfer rate. The most common signaling method on ISDN U interfaces. This protocol is defined in detail in 1988 ANSI spec T1.601.

block multiplexer channel

IBM-style channel that implements the FIPS-60 channel, a U.S. channel standard. This channel is also referred to as OEMI channel and 370 block mux channel.

4B/5B Local Fiber

4-byte/5-byte local fiber. Fiber channel physical media used for FDDI and ATM. Supports speeds of up to 100 Mbps over multimode fiber.


The internet's experimental IPv6 network.


Set of IEEE standards for the definition of LAN protocols.


Short form of RFC 822. Refers to the format of Internet style e-mail as defined in RFC 822.

8B/10B Local fiber

8-byte/10-byte local fiber. Fiber channel physical media that supports speeds up to 149.76 Mbps over multimode fiber.

A&B bit signaling

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 signaling information. Also called 24th channel signaling


authentication, authorization, and accounting.


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 CBR 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.


ATM adaptation layer. 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.


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.


ATM adaptation layer 3/4. One of four AALs (merged from two initially distinct adaptation layers) recommended by the ITU-T. AAL3/4 supports both connectionless and connection-oriented links, but is primarily used for the transmission of SMDS packets over ATM networks.


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 classical IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.


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

ABC signaling

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

AARP probe packets

Packets transmitted by AARP that determine if 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.


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.


1. 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. 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.

Abstract Syntax Notation One

Also know as ASN.1. OSI language for describing data types independent of particular computer structures and representation techniques. Described by ISO International Standard 8824.

Access device

Hardware component used in your signaling controller system: access server or mux.

Access method

1. Generally, the way in which network devices access the network medium.

2. Software within an SNA processor that controls the flow of information through a network.

Access list

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).

Access server

Communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. Performs both synchronous and asynchronous routing of supported protocols. Sometimes called a network access server.


Also known as an access unit. Device that provides ISDN access to PSNs.

Accounting management

One of five categories of network management defined by ISO for management of OSI networks. Accounting management subsystems are responsible for collecting network data relating to resource usage.


automatic call distribution. Device or service that automatically reroutes calls to customers in geographically distributed locations served by the same CO.


algebraic code excited linear prediction.


Advanced Communications Function. A group of SNA products that provides distributed processing and resource sharing.


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.


Acknowledgement. Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) occurred. Sometimes abbreviated ACK.


Term used in G.165, "General Characteristics of International Telephone Connections and International Telephone Circuits: Echo Cancellers." ACOM is the combined loss achieved by the echo canceller, which is the sum of the echo return loss, echo return loss enhancement, and nonlinear processing loss for the call.


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.


association control service element. 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 such management tasks as ensuring that tokens are not lost, or that frames do not circulate indefinitely.


ActiveX is a software framework created by Microsoft that adapts its earlier Component Object Model (COM) and Object Linking and Embedding (OLE) technologies for content downloaded from a network, particularly in the context of the World Wide Web.


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


1. network interface card. Board that provides network communication capabilities to and from a computer system. Also called an adapter.

2. Network Information Center. Organization whose functions have been assumed by the InterNIC.


adaptive differential pulse code modulation. Process by which analog voice samples are encoded into high-quality digital signals.

Dynamic adaptive routing

Also called adaptive routing or dynamic routing. Automatic rerouting of traffic based on a sensing and analysis of current actual network conditions, not including cases of routing decisions taken on predefined information.


Advanced Data Communications Control Protocol. ANSI standard bit-oriented data link control protocol.


Data structure or logical convention used to identify a unique entity, such as a particular process or network device.

Addressed call mode

Mode that permits control signals and commands 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.

Address mask

Bit combination used to describe which portion of an address refers to the network or subnet and which part refers to the host. Sometimes referred to simply as mask.

Address resolution

Generally, a method for resolving differences between computer addressing schemes. Address resolution usually specifies a method for mapping network layer (Layer 3) addresses to data link layer (Layer 2) addresses.


Address Resolution Protocol. Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.


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.


Relationship formed between selected neighboring routers and end nodes for the purpose of exchanging routing information. Adjacency is based upon the use of a common media segment.

Adjacent nodes

1. 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).


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


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

Administrative distance

Rating of the trustworthiness of a routing information source. Administrative distance is often expressed as a numerical value between 0 and 255. The higher the value, the lower the trustworthiness rating.


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.


asymmetric digital subscriber line. One of four DSL technologies. ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream. Downstream rates range from 1.5 to 9 Mbps, while upstream bandwidth ranges from 16 to 640 kbps. ADSL transmissions work at distances up to 18,000 feet (5,488 meters) over a single copper twisted pair.


ATM DSU. Terminal adapter used to access an ATM network via an HSSI-compatible device.

Advanced CoS management

advanced class-of-service management. Essential for delivering the required QoS to all applications. Cisco switches contain per-VC queuing, per-VC rate scheduling, multiple CoS queuing, and egress queuing. This enables network managers to refine connections to meet specific application needs. Formerly called FairShare and OptiClass.


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.


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.


authority and format identifier. Portion of an NSAP-format ATM address that identifies the type and format of the IDI portion of an ATM address.


AppleTalk Filing Protocol. Presentation-layer protocol that allows users to share data files and application programs that reside on a file server. AFP supports AppleShare and Mac OS File Sharing.


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.


Advanced Intelligent Network. In SS7, an expanded set of network services made available to the user, and under user control, that requires improvement in network switch architecture, signaling capabilities, and peripherals.


Asynchronous input/output.


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.


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.


SNMP message notifying an operator or administrator of a network problem.


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.


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.


Generally, an individual, manageable network device. Sometimes called an alias.

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.


SS7 access link. Dedicated SS7 signaling link not physically associated with any particular link carrying traffic.

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.

ALO transaction

ATP transaction in which the request is repeated until a response is received by the requester or until a maximum retry count is reached. This recovery mechanism ensures that the transaction request is executed at least once.


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 independently of the data stream. Sometimes called binary coded alternate mark inversion. Compare with B8ZS.


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.


AMA Teleprocessing System. In OSS, the Bellcore legacy system for collecting and transporting AMA data from central office switches to a billing system. The AMATPS consists of an AMA transmitter and a collector.


Automatic numbering plan


American National Standards Institute. Voluntary organization composed 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.


American Standard Code for Information Interchange. 8-bit code for character representation (7 bits plus parity).


Maximum value of an analog or a digital waveform.


amplitude modulation. Modulation technique whereby information is conveyed through the amplitude of the carrier signal. Compare with FM and PAM.

Analog transmission

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.


automatic number identification. SS7 (signaling system 7) feature in which a series of digits, either analog or digital, are included in the call, identifying the telephone number of the calling device. In other words, ANI identifies the number of the calling party.

anonymous FTP

Allows a user to retrieve documents, files, programs, and other archived data from anywhere on 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.


Number assigned to the ANSI Task Group of Accredited Standards Committee for their internal, working document describing FDDI.


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.


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


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.


adjacent point code. The point code of the next hop in the system for the bearer channels; usually it is the STP (signal transfer point).


Application Programming Interface. Specification of function-call conventions that defines an interface to a service.


Asia Pacific Network Information Center. Nonprofit Internet registry organization for the Asia Pacific region. The other Internet registries are currently IANA, RIPE NCC and InterNIC.

Apollo Domain

Proprietary network protocol suite developed by Apollo Computer for communication on proprietary Apollo networks.


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. It consists of two interfaces: programming and data-exchange. The programming interface replies to requests from programs requiring communication; the data-exchange interface establishes sessions between programs. APPC runs on LU 6.2 devices.


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


Series of communications protocols designed by Apple Computer consisting of two phases. Phase 1, the earlier version, supports a single physical network that can have only one network number and be in one zone. Phase 2, supports multiple logical networks on a single physical network and allows networks to be in more than one zone.


Program that performs a function directly for a user. FTP and Telnet clients are examples of network applications.

Application layer

Layer 7 of the OSI reference model. This layer provides services to application processes (such as e-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.


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+.


Next-generation APPN that replaces 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 fiber cut.


AppleTalk Remote Access. Protocol that provides Macintosh users direct access to information and resources at a remote AppleTalk site.


American Registry for Internet Numbers. Nonprofit organization established for the purpose of administrating and registrating 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. Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.


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).


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.


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


Alarm relay unit


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).


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.


Agent-set control unit


ATM service interface


Auxiliary signal network


Abstract Syntax Notation One. OSI language for describing data types independent of particular computer structures and representation techniques. Described by ISO International Standard 8824.


1. AppleTalk Session Protocol. Protocol that uses ATP to provide session establishment, maintenance, and teardown, as well as request sequencing. See also ATP.

2. Telecommunications: Auxiliary signal path. Link between TransPaths that allows them to exchange signaling information that is incompatible with the PSTN backbone network; used to provide feature transparency.

Assigned numbers

RFC [STD2] documents the currently assigned values from several series of numbers used in network protocol implementations. This RFC is updated periodically, and current information can be obtained from the IANA. If you are developing a protocol or application that will require the use of a link, socket, port, protocol, and so forth, contact the IANA to receive a number assignment.

Associative memory

Memory that is accessed based on its contents, not on its memory address. Sometimes called content addressable memory (CAM).


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.


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.


A subset of tty

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.


AppleTalk Control Protocol. Protocol that establishes and configures AppleTalk over PPP, as defined in RFC 1378.


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.


Attention hangup


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 ARP Server

Device that provides address-resolution services to LISs when running classical IP over ATM.

ATM endpoint

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 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 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.


1. of or requiring a form of computer control timing protocol in which a specific operation begins upon receipt of an indication (signal) that the preceding operation has been completed.

2.not going at the same rate and exactly together with something else, in particular.


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

ATM network

Traditional Cisco ATM network built around BPX switches.

ATM network interface card

Also known as ATM NIC. ESP card that is used as the OC-3 interface to the BPX's BXM.


ATM UNI. User-Network Interface. ATM Forum specification that defines an interoperability standard for the interface between ATM-based products (a router or an ATM switch) located in a private network and the ATM switches located within the public carrier networks. Also used to describe similar connections in Frame Relay networks.

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.


AppleTalk Transaction Protocol. Transport-level protocol that provides a loss-free transaction service between sockets. The service allows exchanges between two socket clients in which one client requests the other to perform a particular task and to report the results. ATP binds the request and response together to ensure the reliable exchange of request-response pairs.


System that provides lists of anonymous FTP archives.


Attached Resource Computer Network. 2.5-Mbps token-bus LAN developed in the late 1970s and early 1980s by Datapoint Corporation.


Logical set of network segments (CLNS-, DECnet-, or OSPF-based) and their attached devices. Areas are usually connected to other areas via routers, making up a single autonomous system.


attachment unit interface. IEEE 802.3 interface between an MAU and a NIC. The term AUI can also refer to the rear panel port to which an AUI cable might attach. Also called transceiver cable.


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.


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, AURP maintains routing tables for the entire AppleTalk WAN by exchanging routing information between exterior routers.

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).


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

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 failed trunk line.

Automatic Routing Management

Formerly AutoRoute. Connection-oriented mechanism used in Cisco WAN switches to provide connectivity across the network. Switches perform a connection admission control (CAC) function on all types of connections in the network. Distributed network intelligence enables the CAC function to automatically route and reroute connections over optimal paths, while guaranteeing the required QoS.

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 AS.


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

Average rate, in kilobits per second (kbps), at which a given virtual circuit will transmit


ATM voice multiplexer.


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 over 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.


Part of a network that acts as the primary path for traffic that is most often sourced from, and destined for, other networks.

back end

Node or software program that provides services to a front end.


The (usually random) retransmission delay enforced by contentious MAC protocols after a network node with data to transmit determines that the physical medium is already in use.


Physical connection between an interface processor or card and the data buses and the power distribution buses inside a chassis.

Back pressure

Propagation of network congestion information upstream through an internetwork.

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.

Back pressure

Propagation of network congestion information upstream through an internetwork.

Balanced configuration

In HDLC, a point-to-point network configuration with two combined stations.


balanced, unbalanced. Device used for matching impedance between a balanced and an unbalanced line, usually twisted-pair and coaxial cable.


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.

Bandwidth reservation

Process of assigning bandwidth to users and applications served by a network. Involves assigning 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.

Bandwidth reservation

Process of assigning bandwidth to users and applications served by a network. Involves assigning 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.


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.


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.


Bourne-again shell. Interactive UNIX shell based on the traditional Bourne shell, but with increased functionality.


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.


Bolt, Beranek, and Newman, Inc. High-technology company located in Massachusetts that developed and maintained the ARPANET (and later, the Internet) core gateway system.

BBN Planet

Subsidiary company of BBN that operates a nationwide Internet access network composed in part by the former regional networks BARRNet, NEARNET, and SURAnet.


Committed Burst. Negotiated tariff metric in Frame Relay internetworks. The maximum amount of data (in bits) that a Frame Relay internetwork is committed to accept and transmit at the CIR.

B channel

bearer channel. In ISDN, a full-duplex, 64-kbps channel used to send user data. Compare to D channel, E channel, and H channel.


Best Current Practices. The newest subseries of RFCs that are written to describe BCPs in the Internet. Rather than specifying a protocol, these documents specify the best ways to use the protocols and the best ways to configure options to ensure interoperability between various vendors' products.


Broadband Digital Cross-Connect System. SONET DCS capable of cross-connecting DS-3, STS-1 and STS-3c signals.


excess burst. Negotiated tariff metric in Frame Relay internetworks. The number of bits that a Frame Relay internetwork will attempt to transmit after Bc is accommodated. Be data is, in general, delivered with a lower probability than Bc data because Be data can be marked as DE by the network.


Frame from a Token Ring or FDDI device indicating a serious problem with the ring, such as a broken cable. A beacon frame contains the address of the station assumed to be down.


backward explicit congestion notification. Bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow control action as appropriate. Compare with FE.


Bell Communications Research. Organization that performs research and development on behalf of the RBOCs.


1. bit error rate. Ratio of received bits that contain errors.

2. basic encoding rules. Rules for encoding data units described in the ISO ASN.1 standard.


bit error rate tester. Device that determines the BER on a given communications channel.

Best-effort delivery

Describes a network system that does not use a sophisticated acknowledgment system to guarantee reliable delivery of information.


Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP exchanges reachability information with other BGP systems. It is defined by RFC 1163.


BGP Version 4. Version 4 of the predominant interdomain routing protocol used on the Internet. BGP4 supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables.


burned-in MAC address.


Broadband Inter-Carrier Interface. ITU-T standard that defines the protocols and procedures needed for establishing, maintaining, and terminating broadband switched virtual connections between public networks.


Bus Interface Gate Array. Technology that allows the Catalyst 5000 to receive and transmit frames from its packet-switching memory to its MAC local buffer memory without the intervention of the host processor.


Method of storing or transmitting data in which the most significant bit or byte is presented first. Compare with little-endian.


Numbering system characterized by ones and zeros (1 = on, 0 = off).


Berkeley Internet Name Domain. Implementation of DNS developed and distributed by the University of California at Berkeley (United States). Many Internet hosts run BIND, which is the ancestor of many commercial BIND implementations.


Binary Hexadecimal. Method for converting binary files into ASCII for transmission by applications, such as e-mail, that can only handle ASCII.


bit interleaved parity. In ATM, a method used to monitor errors on a link. A check bit or word is sent in the link overhead for the previous block or frame. Bit errors in the payload can then be detected and reported as maintenance information.

Biphase coding

Bipolar coding scheme originally developed for use in Ethernet. Clocking information is embedded into and recovered from the synchronous data stream without the need for separate clocking leads. The biphase signal contains no direct current energy.


Electrical characteristic denoting a circuit with both negative and positive polarity. Contrast with unipolar.


Broadband ISDN. ITU-T communication standards designed to handle high-bandwidth applications such as video. BISDN currently uses ATM technology over SONET-based transmission circuits to provide data rates from 155 to 622 Mbps and beyond. Contrast with N-ISDN.


Binary Synchronous Communication Protocol. Character-oriented data-link protocol for applications. Contrast with Synchronous Data Link Control (SDLC).


Binary digit used in the binary numbering system. Can be 0 or 1.


"Because It's Time" Networking Services. Low-cost, low-speed academic network consisting primarily of IBM mainframes and 9600-bps leased lines. BITNET is now part of CREN.


Dial-up service providing connectivity for members of CREN.

Bit-oriented protocol

Class of data link layer communication protocols that can transmit frames regardless of frame content. Unlike byte-oriented protocols, bit-oriented protocols provide full-duplex operation and are more efficient and reliable. Compare with byte-oriented protocol.

Bit rate

Speed at which bits are transmitted, usually expressed in bits per second.

Black hole

Routing term for an area of the internetwork where packets enter, but do not emerge, due to adverse conditions or poor system configuration within a portion of the network.


In a switching system, a condition in which no paths are available to complete a circuit. The term is also used to describe a situation in which one activity cannot begin until another is completed.


Internal cooling fan used in larger router and switch chassis.


Bidirectional Line Switch Ring. SONET ring architecture that provides working and protection fibers between nodes. If the working fiber between nodes is cut, traffic is automatically routed onto the protection fiber.

BBC connector

Standard connector used to connect IEEE 802.3 10Base2 coaxial cable to an MAU.

Broadband network interface



Broadband Network Module.


boundary network node. In SNA terminology, a subarea node that provides boundary function support for adjacent peripheral nodes. This support includes sequencing, pacing, and address translation. Also called boundary node.


boundary network node. In SNA terminology, a subarea node that provides boundary function support for adjacent peripheral nodes. This support includes sequencing, pacing, and address translation. Also called boundary node.


Bell operating company. Twenty-two local phone companies formed by the breakup of AT&T. See RBOC.


Bootstrap Protocol. Protocol used by a network node to determine the IP address of its Ethernet interfaces, in order to affect network booting.

boot PROM

boot programmable read-only memory. Chip mounted on a printed circuit board used to provide executable boot instructions to a computer device.

Border Gateway

Router that communicates with routers in other autonomous systems.

Boundary function

Capability of SNA subarea nodes to provide protocol support for attached peripheral nodes. Typically found in IBM 3745 devices.


Bridge Protocol Data Unit. Spanning-Tree Protocol hello packet that is sent out at configurable intervals to exchange information among bridges in the network.


baseline privacy interface.


Bits per second


bipolar violation.

BPI service node

Closely integrated BPX switch, AXIS interface shelf, and extended services processor designed to support ATM and Frame Relay switched virtual circuits, as well as traditional PVCs.


break-out/break-in. VNS feature that allows interworking between Euro-ISDN (ETSI) and other VNS-supported signaling variants, such as DPNSS and QSIG.


Basic Research and Human Resources. Component of the HPCC program designed to support research, training, and education in computer science, computer engineering, and computational science.


bridge relay function.


Basic Rate Interface. ISDN interface composed of two B channels and one D channel for circuit-switched communication of voice, video, and data. Compare with PRI.


Device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (Layer 2) of the OSI reference model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame.

Bridge forwarding

Process that uses entries in a filtering database to determine whether frames with a given MAC destination address can be forwarded to a given port or ports. Described in the IEEE 802.1 standard.

Bridge group

Bridging feature that assigns network interfaces to a particular spanning-tree group. Bridge groups can be compatible with the IEEE 802.1 or the DEC specification.

Bridge numbers

Number that identifies each bridge in an SRB LAN. Parallel bridges must have different bridge numbers.

bridge static filtering

Process in which a bridge maintains a filtering database consisting of static entries. Each static entry equates a MAC destination address with a port that can receive frames with this MAC destination address and a set of ports on which the frames can be transmitted. Defined in the IEEE 802.1 standard.


1. Transmission system that multiplexes multiple independent signals onto one cable.

2. Telecommunications terminology: Any channel having a bandwidth greater than a voice-grade channel (4 kHz).

3. LAN terminology: A coaxial cable on which analog signaling is used. Also called wideband. Contrast with baseband.


Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast address. Compare with multicast and unicast.

Broadcast address

Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones. Compare with multicast address and unicast address.

Broadcast address

Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones. Compare with multicast address and unicast address.

Broadcast domain

Set of all devices that will receive broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers because routers do not forward broadcast frames.

Broadcast search

Propagation of a search request to all network nodes if the location of a resource is unknown to the requester.

Broadcast storm

Undesirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and, typically, causes network time-outs.


Concatenation of "bridge" and "router." Used to refer to devices which perform both bridging and routing functions.


GUI-based hypertext client application, such as Internet Explorer, Mozilla, and Chome use to access hypertext documents and other services located on innumerable remote servers throughout the WWW and Internet.


binary synchronous communication. Character-oriented data link layer protocol for half-duplex applications. A form of telecommunication line control that uses a standard set of transmission control characters and control character sequences, for binary synchronous transmission of binary-coded data between stations. Often referred to simply as .


Berkeley Standard Distribution. Term used to describe any of a variety of UNIX-type operating systems based on the UC Berkeley BSD operating system.


Block Serial Tunneling.


burst tolerance. Parameter defined by the ATM Forum for ATM traffic management. For VBR connections, BT determines the size of the maximum burst of contiguous cells that can be transmitted.


British thermal units


Storage area used for handling data in transit. Buffers are used in internetworking to compensate for differences in processing speed between network devices. Bursts of data can be stored in buffers until they can be handled by slower processing devices. Sometimes referred to as a packet buffer.


Create flat files that are ready for use by the signaling controller database.


broadcast and unknown server. Multicast server used in ELANs that is used to flood traffic addressed to an unknown destination and to forward multicast and broadcast traffic to the appropriate clients.


Common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another. Sometimes called highway.

Bus topology

Linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations. Compare with ring topology, star topology, and tree topology.


Bridge Group Virtual Interface.


Broadband Switch Module.

Bypass mode

Operating mode on FDDI and Token Ring networks in which an interface has been removed from the ring.

Bypass relay

Allows a particular Token Ring interface to be shut down and thus effectively removed from the ring.

Bypass relay

Allows a particular Token Ring interface to be shut down and thus effectively removed from the ring.


Term used to refer to a series of consecutive binary digits that are operated upon as a unit (for example, an 8-bit byte).

byte-oriented protocol

Class of data-link communications protocols that use a specific character from the user character set to delimit frames. These protocols have largely been replaced by bit-oriented protocols. Compare with bit-oriented protocol.

Byte reversal

Process of storing numeric data with the least-significant byte first. Used for integers and addresses on devices with Intel microprocessors.


1. certification authority.

2. Telecommunications: call appearance.


Transmission medium of copper wire or optical fiber wrapped in a protective cover.

Cable range

Range of network numbers that is valid for use by nodes on an extended AppleTalk network. The cable range value can be a single network number or a contiguous sequence of several network numbers. Node addresses are assigned based on the cable range values.


connection admission control. Set of actions taken by each ATM switch during connection setup in order to determine whether a connection's requested QoS will violate the QoS guarantees for established connections. CAC is also used when routing a connection request through an ATM network.


Form of replication in which information learned during a previous transaction is used to process later transactions.


controllable ATM fabric.


Piece of hardware into which cards are installed.


Call Detail Record. VNS record of voice or data SVCs, which includes calling and called numbers, local and remote node names, data and timestamp, elapsed time, and Call Failure Class fields.

Call leg

Discrete segment of a call connection. A call leg is a logical connection between the router and either a telephony endpoint over a bearer channel, or another endpoint using a session protocol.

Call priority

Priority assigned to each origination port in circuit-switched systems. This priority defines the order in which calls are reconnected. Call priority also defines which calls can or cannot be placed during a bandwidth reservation.

Call setup time

Time required to establish a switched call between DTE devices.


1. Cisco access manager

2. content-addressable memory.


Competitive Access Provider. Independent company providing local telecommunications services mainly to business customers in competition with an area's BOC or IOC. Teleport and MFS are the two major CAPs operating in major metropolitan areas in the United States.


Electromagnetic wave or alternating current of a single frequency, suitable for modulation by another, data-bearing signal.


channel associated signaling.

Category 1 cabling

One of twelve grades of UTP cabling described in the EIA/TIA-586 standard. Category 1 cabling is used for telephone communications and is not suitable for transmitting data. Unsuitable for modern systems

Category 2 cabling

One of twelve grades of UTP cabling described in the EIA/TIA-586 standard. Category 2 cabling is capable of transmitting data at speeds up to 4 Mbps.Unsuitable for modern systems

Category 3 Cabling

UTP (unshielded twisted pair). Bandwidth of 16 MHz. Applications are10BASE-T and 100BASE-T4 Ethernet.Described in EIA/TIA-568. Unsuitable for speeds above 16 Mbit/s. Now mainly for telephone cables

Category 4 Cabling

UTP (unshielded twisted pair). Badwidth Rating of20 MHz. Applications: speeds up to 16 Mbit/s and Token Ring.Not commonly used.

Category 5 Cabling

Unshielded twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. The cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet). Superseded by Cat5e, but most Cat5 cable meets Cat5e standards

Category 5e Cabling

Category 5e specification improves upon the category 5 specification by tightening some crosstalk specifications and introducing new crosstalk specifications that were not present in the original category 5 specification.[13] The bandwidth of category 5 and 5e is the same (100 MHz) and the physical cable construction is the same, most Cat5 cable meets Cat5e specifications, though it is not tested or certified as such.

Category 6 Cabling

Standardized cable for Gigabit Ethernet and other network physical layers. Backward compatible with the Category 5/5e and Category 3 cable standards. Cat 6 features more stringent specifications for crosstalk and system noise.Performance of up to 250 MHz Suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), 1000BASE-T/1000BASE-TX (Gigabit Ethernet), and 10GBASE-T (10-Gigabit Ethernet)

Category 6a Cabling

Can be a shielded twisted pair (U/FTP) or screened twisted pair (F/UTP). Improves bandwidth capabilities to 500 MHz and adds cable shielding to further reduce alien crosstalk.

Category 7 Cabling

F/FTP, S/FTP (Screened shielded twisted pair)Bandwidth of 600 MHz. Applications include:Telephone, CCTV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet.Category 7 cables are fully shielded cables.

Category 7a Cabling

F/FTP, S/FTP (Screened shielded twisted pair) fully shielded. Bandwidth of1000 MHz.Applications include: Telephone, CATV, 1000BASE-TX in the same cable. 10GBASE-T Ethernet. This cable uses all four pairs. ISO/IEC 11801 2nd Ed. Am. 2.

Category 8.1 Cabling

U/FTP (foil shielding around the pairs), F/UTP (foil shielding around the cable). Bandwidthof 1600-2000 MHz. Applications include:Telephone, CATV, 1000BASE-TX in the same cable. 40GBASE-T Ethernet.This cable is still in development.

Category 8.2 Cabling

F/FTP (foil shielding on both pair and cable), S/FTP (shielding on the cable in braided, shielding for individual pairs is foil) Bandwidth of1600-2000 MHz.Applications include: Telephone, CATV, 1000BASE-TX in the same cable. 40GBASE-T Ethernet. This cable is still in development.


Category 5, four pair UTP wiring up to 100m long with speeds up to 1 Gbps


Copper twisted pair called twinax (a balanced coaxial pair) that can run only up to 25 m and uses a special 9-pin connector known as the High Speed Serial Data Connector (HSSDC).


The implementation of 1 Gigabit Ethernet running over multimode fiber-optic cable (instead of copper twisted-pair cable) and using short wavelength laser. Multimode fiber (MMF) using 62.5- and 50- micron core: uses and 850 nanometer (nm) laser and can go up to 220m with 62.5- micron or 550m with 50- micron.


Single-mode fiber that uses a 9-micron core and 1300nm laser and can go from 3 km up to 10 km.


Standard proposed by the IEEE 802.3as committee to provide 10Gbps connections over conventional UTP cables (categories 5e, 6, or 7). 10GBaseT allows the conventional RJ-45 used for Ethernet LANs. It can support signal transmission at the full 100m distance specified for LAN wiring.

10GBase-Short Range (SR)

An implementation of 10 Gigabit Ethernet that uses short-wavelength lasers at 850nm over multimode fiber. It has a maximum transmission distance of between 2-300m, depending on the size and quality of the fiber.

10GBase-Long Range (LR)

An implementation of 10 Gigabit Ethernet that uses long-wavelength lasers at 1,310nm over single-mode fiber. It also has a maximum transmission distance between 2m and 10km, depending on the size and quality of the fiber.

10GBase-Extended Range (ER)

An implementation of 10 Gigabit Ethernet running over single-mode fiber. It uses extra-long-wavelength lasers at 1,550 nm. It has the longest transmission distance of the 10Gb technologies: anywhere from 2m to 40km, depending on the size and quality of the fiber.

10GBase-Short Wavelength (SW)

A mode of 10Base-S for MMF with a 850nm laser transceiver with a bandwidth of 10Gbps. I can support up to 300m of cable length. This media type is designed to connect to SONET equipment.

10GBase-Long Wavelength (LW)

Mode of 10GBase-L supporting a link length of 10km on a standard single-mode fiber (SMF)(G.652). This media type is designed to connect to SONET equipment.

10GBase-Extra Long Wavelength (EW)

Mode of 10GBaseE supporting a link length of up to 40km on SMF (single-mode fiber) based on G.652 using optical-wavelength 1,550nm. This media type is designed to connect to SONET equipment.


Network in which hosts are connected to diverse networks, which themselves are connected with routers. The Internet is a prominent example of a catenet.


cable television. Communication system where multiple channels of programming material are transmitted to homes using broadband coaxial cable. Formerly called Community Antenna Television.


Context-based Access Control. Protocol that provides internal users with secure access control for each application and for all traffic across network perimeters. CBAC enhances security by scrutinizing both source and destination addresses and by tracking each application's connection status.


Connectionless Broadband Data Service. European high-speed, packet-switched, datagram-based WAN networking technology. Similar to SMDS.


constant bit rate. QoS class defined by the ATM Forum for ATM networks. CBR is used for connections that depend on precise clocking to ensure undistorted delivery. Compare with ABR, UBR, and VBR.


call control block.


Consultative Committee for International Telegraph and Telephone. International organization responsible for the development of communications standards. Now called the ITU-T.


cross office transfer time.


commitment, concurrency, and recovery. OSI application service element used to create atomic operations across distributed systems. Used primarily to implement two-phase commit for transactions and nonstop operations.


common channel signaling. Signaling system used in telephone networks that separates signaling information from user data. A specified channel is exclusively designated to carry signaling information for all other channels in the system.


Carrier Detect. Signal that indicates whether an interface is active. Also, a signal generated by a modem indicating that a call has been connected.


Copper Distributed Data Interface. Implementation of FDDI protocols over STP and UTP cabling. CDDI transmits over relatively short distances (about 90 yards [100 meters]), providing data rates of 100 Mbps using a dual-ring architecture to provide redundancy. Based on the ANSI TPPMD standard. Compare with FDDI.


channel definition format. Technology for "push" applications on the World Wide Web. CDF is an application of XML.


Cisco Discovery Protocol. Media- and protocol-independent device-discovery protocol that runs on all Cisco-manufactured equipment including routers, access servers, bridges, and switches. Using CDP, a device can advertise its existence to other devices and receive information about other devices on the same LAN or on the remote side of a WAN. Runs on all media that support SNAP, including LANs, Frame Relay, and ATM media.


Cellular Digital Packet Data. Open standard for two-way wireless data communication over high-frequency cellular telephone channels. Allows data transmissions between a remote cellular link and a NAP. Operates at 19.2 Kbps.


call detail record. VNS record of voice or data SVCs, which includes calling and called numbers, local and remote node names, data and timestamp, elapsed time, and Call Failure Class fields.


cell delay variation. Component of cell transfer delay, which is induced by buffering and cell scheduling. CDV is a QoS delay parameter associated with CBR and VBR service.


cell delay variation tolerance. In ATM, a QoS parameter for managing traffic that is specified when a connection is set up. In CBR transmissions, CDVT determines the level of jitter that is tolerable for the data samples taken by the PCR.


Cisco express forwarding.


Basic data unit for ATM switching and multiplexing. Cells contain identifiers that specify the data stream to which they belong. Each cell consists of a 5-byte header and 48 bytes of payload.

Cell payload scrambling

Technique using an ATM switch to maintain framing on some medium-speed edge and trunk interfaces.

Cell relay

Network technology based on the use of small, fixed-size packets, or cells. Because cells are fixed-length, they can be processed and switched in hardware at high speeds. Cell relay is the basis for many high-speed network protocols including ATM, IEEE 802.6, and SMDS.

cells per second

Abbreviated cps.

Cellular radio

Technology that uses radio transmissions to access telephone-company networks. Service is provided in a particular area by a low-power transmitter.


code excited linear prediction compression. Compression algorithm used in low bit-rate voice encoding. Used in ITU-T Recommendations G.728, G.729, G.723.1.


LEC service that provides local switching applications similar to those provided by an onsite PBX. With Centrex, there is no onsite switching; all customer connections go back to the CO.


Conférence Européenne des Postes et des Télécommunications. Association of the 26 European PTTs that recommends communication specifications to the ITU-T.


cell error ratio. In ATM, the ratio of transmitted cells that have errors to the total cells sent in a transmission for a specific period of time.


California Education and Research Federation Network. TCP/IP network, based in Southern California, that connects hundreds of higher-education centers internationally while also providing Internet access to subscribers. CERFnet was founded in 1988 by the San Diego Supercomputer Center and General Atomics, and is funded by the NSF.


European Laboratory for Particle Physics. Birthplace of the World Wide Web.


Computer Emergency Response Team. Chartered to work with the Internet community to facilitate its response to computer security events involving Internet hosts, to take proactive steps to raise the community's awareness of computer security issues, and to conduct research targeted at improving the security of existing systems. The U.S. CERT is based at Carnegie Mellon University in Pittsburgh (United States), Regional CERTs are, like NICs, springing up in different parts of the world.


circuit emulation service. Enables users to multiplex or concentrate multiple circuit emulation streams for voice and video with packet data on a single high-speed ATM link without a separate ATM access multiplexer.


Also called Cisco FRAD. Cisco Frame Relay access device. Cisco product that supports Cisco IOS Frame Relay SNA services and can be upgraded to be a full-function multiprotocol router. The Cisco FRAD connects SDLC devices to Frame Relay without requiring an existing LAN. However, the Cisco FRAD does support attached LANs and can perform conversion from SDLC to Ethernet and Token Ring. See also FRAD.


Common Gateway Interface. Set of rules that describe how a Web server communicates with another application running on the same computer and how the application (called a CGI program) communicates with the Web server. Any application can be a CGI program if it handles input and output according to the CGI standard.


SNA concept in which RUs are grouped together for the purpose of error recovery.


1. Communication path. Multiple channels can be multiplexed over a single cable in certain environments.

2. In IBM, the specific path between large computers (such as mainframes) and attached peripheral devices.

3. Specific frequency allocation and bandwidth. Downstream channels are used for television in the United States are 6 MHz wide.


Pertaining to attachment of devices directly by data channels (input/output channels) to a computer.

Channelized E1

Access link operating at 2.048 Mbps that is subdivided into 30 B-channels and 1 D-channel. Supports DDR, Frame Relay, and X.25. Compare with channelized T1.

Channelized T1

Access link operating at 1.544 Mbps that is subdivided into 24 channels (23 B-channels and 1 D-channel) of 64 Kbps each. The individual channels or groups of channels connect to different destinations. Supports DDR, Frame Relay, and X.25. Also called fractional T1. Compare with channelized E1.


Challenge Handshake Authentication Protocol. Security feature supported on lines using PPP encapsulation that prevents unauthorized access. CHAP does not itself prevent unauthorized access, it merely identifies the remote end. The router or access server then determines whether that user is allowed access. Compare to PAP.

chat script

String of text that defines the login "conversation" that occurs between two systems. Consists of expect-send pairs that define the string that the local system expects to receive from the remote system and what the local system should send as a reply.


Method for checking the integrity of transmitted data. A checksum is an integer value computed from a sequence of octets taken through a series of arithmetic operations. The value is recomputed at the receiving end and compared for verification.

Child peer group

Peer group for which another peer group is the parent peer group.

choke packet

Packet sent to a transmitter to tell it that congestion exists and that it should reduce its sending rate.


classical IP over ATM. Specification for running IP over ATM in a manner that takes full advantage of the features of ATM. Defined in RFC 1577.


Regional network that connects academic, research, nonprofit, and commercial organizations in the Midwestern United States. Founded in 1988, CICNet was a part of the NSFNET and was funded by the NSF until the NSFNET dissolved in 1995.


Customer Information Control System. IBM application subsystem allowing transactions entered at remote terminals to be processed concurrently by user applications.


1. craft interface device. Terminal or PC-based interface that enables the performance of local maintenance operations.

2. channel ID. Designates the Frame Relay subchannel ID for Voice over Frame Relay.


classless interdomain routing. Technique supported by BGP4 and based on route aggregation. CIDR allows routers to group routes together in order to cut down on the quantity of routing information carried by the core routers. With CIDR, several IP networks appear to networks outside the group as a single, larger entity. With CIDR, IP addresses and their subnet masks are written as 4 octets, separated by periods, followed by a forward slash and a 2-digit number that represents the subnet mask.


committed information rate. Rate at which a Frame Relay network agrees to transfer information under normal conditions, averaged over a minimum increment of time. CIR, measured in bits per second, is one of the key negotiated tariff metrics.


Communications path between two or more points.

Circuit group

Grouping of associated serial lines that link two bridges. If one of the serial links in a circuit group is in the spanning tree for a network, any of the serial links in the circuit group can be used for load balancing. This load-balancing strategy avoids data ordering problems by assigning each destination address to a particular serial link.

circuit steering

Mechanism used by some ATM switches to eavesdrop on a virtual connection and copy its cells to another port where an ATM analyzer is attached. Also known as port snooping.

Circuit switching

Switching system in which a dedicated physical circuit path must exist between sender and receiver for the duration of the "call." Used heavily in the telephone company network. Circuit switching can be contrasted with contention and token passing as a channel-access method, and with message switching and packet switching as a switching technique.


Proprietary Cisco protocol based on ISUP.


Cisco internetworking architecture that "fuses" together the scalability, stability, and security advantages of the latest routing technologies with the performance benefits of ATM and LAN switching, and the management benefits of VLANs.

Cisco IOS

Cisco system software that provides common functionality, scalability, and security for all products under the CiscoFusion architecture. Cisco IOS allows centralized, integrated, and automated installation and management of internetworks, while ensuring support for a wide variety of protocols, media, services, and platforms.


Cisco link services. A front-end for a variety of data-link control services.


Cisco Link Services Interface. Messages that are exchanged between CLS and data-link users such as APPN, SNA service point, and DLSw+.

Cisco-trunk (private line) call

A Cisco-trunk (private line) call is established by the forced connection of a dynamic switched call. A Cisco-trunk call is established during configuration of the trunk and stays up for the duration of the configuration. It optionally provides a pass-through connection path to pass signaling information between the two telephony interfaces at either end of the connection.


GUI-based device-management software application that provides dynamic status, statistics, and comprehensive configuration information for Cisco internetworking devices. In addition to displaying a physical view of Cisco device chassis, CiscoView also provides device monitoring functions and basic troubleshooting capabilities, and can be integrated with several leading SNMP-based network management platforms.


Commercial Internet Exchange. A connection point between the commercial Internet service providers. Pronounced "kicks."


Common Link Access for Workstations. Data link layer protocol used by channel-attached RISC System/6000 series systems and by IBM 3172 devices running TCP/IP off-load. CLAW improves efficiency of channel use and allows the CIP to provide the functionality of a 3172 in TCP/IP environments and support direct channel attachment. The output from TCP/IP mainframe processing is a series of IP datagrams that the router can switch without modifications.

Clear channel

Channel that uses out-of-band signaling (as opposed to in-band signaling), so the channel's entire bit rate is available.


competitive local exchange carrier. Company that builds and operates communication networks in metropolitan areas and provides its customers with an alternative to the local telephone company.


1. command line interface. Interface that allows the user to interact with the operating system by entering commands and optional arguments. The UNIX operating system and DOS provide CLIs. Compare with GUI.

2. Command Language Interpreter. Basic Cisco IOS configuration and management interface.


Node or software program (front-end device) that requests services from a server.

client/server computing

Term used to describe distributed computing (processing) network systems in which transaction responsibilities are divided into two parts: client (front end) and server (back end). Both terms (client and server) can be applied to software programs or actual computing devices. Also called distributed computing (processing). Compare with peer-to-peer computing.

Client-Server model

Common way to describe network services and the model user processes (programs) of those services. Examples include the nameserver/nameresolver paradigm of the DNS and fileserver/file-client relationships such as NFS and diskless hosts.


Connectionless Network Protocol. OSI network layer protocol that does not require a circuit to be established before data is transmitted.


Connectionless Network Service. OSI network layer service that does not require a circuit to be established before data is transmitted. CLNS routes messages to their destinations independently of any other messages.


cell loss priority. Field in the ATM cell header that determines the probability of a cell being dropped if the network becomes congested. Cells with CLP = 0 are insured traffic, which is unlikely to be dropped. Cells with CLP = 1 are best-effort traffic, which might be dropped in congested conditions in order to free up resources to handle insured traffic.


cell loss ratio. In ATM, the ratio of discarded cells to cells that are successfully transmitted. CLR can be set as a QoS parameter when a connection is set up.


Connectionless Transport Protocol. Provides for end-to-end Transport data addressing (via Transport selector) and error control (via checksum), but cannot guarantee delivery or provide flow control. The OSI equivalent of UDP.

cluster controller

1. Generally, an intelligent device that provides the connections for a cluster of terminals to a data link.

2. In SNA, a programmable device that controls the input/output operations of attached devices. Typically, an IBM 3174 or 3274 device.


1. coded mark inversion. ITU-T line coding technique specified for STS-3c transmissions. Also used in DS-1 systems.


Common Management Information Protocol. OSI network management protocol created and standardized by ISO for the monitoring and control of heterogeneous networks.


Common Management Information Services. OSI network management service interface created and standardized by ISO for the monitoring and control of heterogeneous networks.


Connection-Mode Network Service. Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring).


connection management. FDDI process that handles the transition of the ring through its various states (off, active, connect, and so on), as defined by the ANSI X3T9.5 specification.


cable modem termination system. Any DOCSIS-compliant headend cable router, such as the Cisco uBR7246.


central office. Local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs.

coaxial cable

Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. Two types of coaxial cable are currently used in LANs: 50-ohm cable, which is used for digital signaling, and 75-ohm cable, which is used for analog signaling and high-speed digital signaling.



1. Integrated circuit device that typically uses pulse code modulation to transform analog signals into a digital bit stream and digital signals back into analog signals.

2. In Voice over IP, Voice over Frame Relay, and Voice over ATM, a DSP software algorithm used to compress/decompress speech or audio signals.


Electrical techniques used to convey binary signals.


central office frame relay access device.


Connection Oriented IPX. Native ATM protocol based on IPX under development by Novell.

collapsed backbone

Nondistributed backbone in which all network segments are interconnected by way of an internetworking device. A collapsed backbone might be a virtual network segment existing in a device such as a hub, a router, or a switch.


In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and are damaged when they meet on the physical media.

collision domain

In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges and routers do not.

common carier

Licensed, private utility company that supplies communication services to the public at regulated prices.


Transmission of information.

communication controller

In SNA, a subarea node (such as an IBM 3745 device) that contains an NCP.

communication server

Communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. Performs only asynchronous routing of IP and IPX. Compare with access server.

communications line

Physical link (such as wire or a telephone circuit) that connects one or more devices to one or more other devices.


In SNMP, a logical group of managed devices and NMSs in the same administrative domain.

community string

Text string that acts as a password and is used to authenticate messages sent between a management station and a router containing an SNMP agent. The community string is sent in every packet between the manager and the agent. Also called a community name.


Contraction derived from the opposite processes of compression and expansion. Part of the PCM process whereby analog signal values are logically rounded to discrete scale-step values on a nonlinear scale. The decimal step number is then coded in its binary equivalent prior to transmission. The process is reversed at the receiving terminal using the same nonlinear scale. Compare with compression and expansion.


The running of a data set through an algorithm that reduces the space required to store or the bandwidth required to transmit the data set. Compare with companding and expansion.


configuration failure. Resource is OOS because its provisioning information is inconsistent.

Configuration direct VCC

In ATM, a bi-directional point-to-point VCC set up by a LEC to an LES. One of three control connections defined by Phase 1 LANE. Compare with control distribute VCC and control direct VCC.

Configuration management

One of five categories of network management defined by ISO for management of OSI networks. Configuration management subsystems are responsible for detecting and determining the state of a network.

configureation register

In Cisco routers, a 16-bit, user-configurable value that determines how the router functions during initialization. The configuration register can be stored in hardware or software. In hardware, the bit position is set using a jumper. In software, the bit position is set by specifying a hexadecimal value using configuration commands.

configuration tool

1. Service management tool with a GUI.

2. Element management service tool with a GUI.


Traffic in excess of network capacity.

congestion avoidance

Mechanism by which an ATM network controls traffic entering the network to minimize delays. In order to use resources most efficiently, lower-priority traffic is discarded at the edge of the network if conditions indicate that it cannot be delivered.

congestion collapse

Condition in which the retransmission of frames in an ATM network results in little or no traffic successfully arriving at the destination. Congestion collapse frequently occurs in ATM networks composed of switches that do not have adequate and effective buffering mechanisms complimented by intelligent packet discard or ABR congestion feedback mechanisms.


Term used to describe data transfer without the existence of a virtual circuit. Compare with connection-oriented.


Term used to describe data transfer that requires the establishment of a virtual circuit.


Connection-Oriented Network Protocol. OSI protocol providing connection-oriented operation to upper-layer protocols.


connection-oriented network service.


DTE through which commands are entered into a host.


Access method in which network devices compete for permission to access the physical medium. Compare with circuit switching and token passing.

control direct VCC

In ATM, a bidirectional VCC set up by a LEC to a LES. One of three control connections defined by Phase 1 LANE. Compare with configuration direct VCC and control distribute VCC.

control distribute VCC

In ATM, a unidirectional VCC set up from a LES to a LEC. One of three control connections defined by Phase 1 LANE. Typically, the VCC is a point-to-multipoint connection. Compare with configuration direct VCC and control direct VCC.


Speed and ability of a group of internetworking devices running a specific routing protocol to agree on the topology of an internetwork after a change in that topology.