Table of Contents




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.

cable television



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.

California Education and Research Federation Network

See CERFnet.

Call Detail Record

See CDR in the "Cisco Systems Terms and Acronyms" section.

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. See also bandwidth reservation.

call reference value

See CRV.

call setup time

Time required to establish a switched call between DTE devices.


content-addressable memory. See associative memory. See also CAM in the "Cisco Systems Terms and Acronyms" section.

Canadian Standards Association

See CSA.


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. See also BOC and IOC.


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

Carrier Detect

See CD.

carrier sense multiple access collision detect

See CSI.


channel associated signaling.

Category 1 cabling

One of five 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. Compare with Category 2 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 2 cabling

One of five 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. Compare with Category 1 cabling, Category 3 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 3 cabling

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 3 cabling is used in 10BaseT networks and can transmit data at speeds up to 10 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 4 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 4 cabling

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 4 cabling is used in Token Ring networks and can transmit data at speeds up to 16 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 5 cabling. See also EIA/TIA-586 and UTP.

Category 5 cabling

One of five grades of UTP cabling described in the EIA/TIA-586 standard. Category 5 cabling can transmit data at speeds up to 100 Mbps. Compare with Category 1 cabling, Category 2 cabling, Category 3 cabling, and Category 4 cabling. See also EIA/TIA-586 and UTP.


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. See also 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. See 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. See also SS7.


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. See XML.


See CDP (Cisco Discovery Protocol) in the "Cisco Systems Terms and Acronyms" section.


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.


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. See also CBR and VBR.


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. See also CBR and PCR.


See CEF in the in the "Cisco Systems Terms and Acronyms" section.


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. See also cell relay.

cell delay variation

See CDV.

cell delay variation tolerance


cell loss priority

See CLP.

cell loss ratio

See CLR.

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. See also cell.

cells per second

Abbreviated cps.

cell transfer delay

See CTD.

Cellular Digital Packet Data


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.

central office

See CO.


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. See also CO and LEC.


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.


See Cisco FRAD in the "Cisco Systems Terms and Acronyms" section.


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.

Challenge Handshake Authentication Protocol



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.

channel definition format.

See CDF.

Channel Interface Processor

See CIP in the "Cisco Systems Terms and Acronyms" section.

channel service unit

See CSU.

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.


Industry term used to refer to the IEEE 802.3 10Base2 standard or the cable specified in that standard. Compare with Thinnet. See also 10Base2, Ethernet, and IEEE 802.3.


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. See also LGN, peer group, and 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. See also NSFNET.


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. See also BGP4.


See CIP (Channel Interface Processor) in the "Cisco Systems Terms and Acronyms" section.


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. See also Bc.


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.


See C-ISUP in the "Cisco Systems Terms and Acronyms" section. See also ISUP.

ciscoBus controller

See SP in the "Cisco Systems Terms and Acronyms" section.

Cisco Discovery Protocol

See CDP in the "Cisco Systems Terms and Acronyms" section.

Cisco FRAD

See Cisco FRAD in the "Cisco Systems Terms and Acronyms" section.

Cisco Frame Relay access device

See Cisco FRAD in the "Cisco Systems Terms and Acronyms" section.


See CiscoFusion in the "Cisco Systems Terms and Acronyms" section.

Cisco Internetwork Operating System software

See Cisco IOS in the "Cisco Systems Terms and Acronyms" section.

Cisco IOS

See Cisco IOS in the "Cisco Systems Terms and Acronyms" section.

Cisco Link Services

See CLS in the "Cisco Systems Terms and Acronyms" section.

Cisco Link Services Interface

See CLSI in the "Cisco Systems Terms and Acronyms" section.

Cisco-trunk (private line) call

See Cisco-trunk (private line) call in the "Cisco Systems Terms and Acronyms" section.


See Cisco-trunk (private line) call in the "Cisco Systems Terms and Acronyms" section.


Commercial Internet Exchange. A connection point between the commercial Internet service providers. Pronounced "kicks." See FIX and GIX.

Class A station

See DAS.

Class B station

See SAS.

classical IP over ATM

See CIA.

classless interdomain routing


class of service

See CoS.


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 To Send

See CTS.

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. See CAP.


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. See also back end, FRF.11, and 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. See also RPC.

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. See also CLNS.


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. See also CLNP.


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. See also DS-1 and STS-3c.

2. control mode idle?


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


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


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


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.

coded mark inversion

See CMI.




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. See also collision domain.

collision detection

See CSI.

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. See also collision.

command line interface

See CLI.

Committed Burst

See Bc.

committed information rate

See CIR.

common carrier

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

common channel signaling

See CCS.

Common Gateway Interface

See CGI.

Common Link Access for Workstations


Common Management Information Protocol


Common Management Information Services


common part convergence sublayer


Common Programming Interface for Communications

See CPI-C.

common transport semantic

See CTS.


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 Antenna Television

Now known as CATV. See CATV.

community name

See community string.

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. See also a-law and mu-law.

complete sequence number PDU


Compressed Serial Link Internet Protocol

See CSI.


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.

Computer Science Network



See hub.


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

Conférence Européenne des Postes et des Télécommunications


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. See also accounting management, fault management, performance management, and security management.

configuration register

See configuration register in the "Cisco Systems Terms and Acronyms" section.

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.

connection admission control

See CAC.


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

Connectionless Broadband Data Service


Connectionless Network Protocol


Connectionless Network Service


connection management

See CMT.

Connection-Mode Network Service



Term used to describe data transfer that requires the establishment of a virtual circuit. See also connectionless and virtual circuit.

Connection-Oriented Network Protocol



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


connection-oriented network service.


DTE through which commands are entered into a host.

constant bit rate

See CBR.

Consultative Committee for International Telegraph and Telephone


content-addressable memory

See associative memory.


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

Context-based Access Control

See CCB.

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.

control point

See CP.


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.

convergence sublayer

See CS.


In SNA, an LU 6.2 session between two transaction programs.


Piece of information sent by a Web server to a Web browser that the browser is expected to save and send back to the Web server whenever the browser makes additional requests of the Web server.

Cooperation for Open Systems Interconnection Networking in Europe



Commanded OOS. A resource is OOS because it was entered as a command. See also OOS in the "Cisco Systems Terms and Acronyms" section.

Copper Distributed Data Interface



Common Open Policy Service. Quality-of-service (QoS) policy exchange protocol proposed as an IETF standard for communicating network QoS policy information.


Common Object Request Broker Architecture. OMG's answer to the need for interoperability among the rapidly proliferating number of hardware and software products available today. Simply stated, CORBA allows applications to communicate with one another no matter where they are located or who has designed them. See IIOP.

core gateway

Primary routers in the Internet.

core router

In a packet-switched star topology, a router that is part of the backbone and that serves as the single pipe through which all traffic from peripheral networks must pass on its way to other peripheral networks.

Corporation for Open Systems

See COS.

Corporation for Research and Educational Networking



class of service. Indication of how an upper-layer protocol requires a lower-layer protocol to treat its messages. In SNA subarea routing, COS definitions are used by subarea nodes to determine the optimal route to establish a given session. A COS definition comprises a virtual route number and a transmission priority field. Also called ToS.


Corporation for Open Systems. Organization that promulgates the use of OSI protocols through conformance testing, certification, and related activities.


Cooperation for Open Systems Interconnection Networking in Europe. European project financed by the EC to build a communication network between scientific and industrial entities in Europe. The project ended in 1994.


Arbitrary value, typically based on hop count, media bandwidth, or other measures, that is assigned by a network administrator and used to compare various paths through an internetwork environment. Cost values are used by routing protocols to determine the most favorable path to a particular destination: the lower the cost, the better the path. Sometimes called path cost. See also routing metric.


Continuity Test. Requirement of the SS7 protocol specifications. It tests the bearer channels' status using either loopback or tone detection and generation. Used to test individual DS0 channels via either loopback or tone detection and generation.

count to infinity

Problem that can occur in routing algorithms that are slow to converge, in which routers continuously increment the hop count to particular networks. Typically, some arbitrary hop-count limit is imposed to prevent this problem.


1. control point. In SNA networks, element that identifies the APPN networking components of a PU 2.1 node, manages device resources, and provides services to other devices. In APPN, CPs are able to communicate with logically adjacent CPs by way of CP-to-CP sessions. See also EN and NN.

2. Telecommunications: control processor.


calling party category.


1. common part convergence sublayer. One of the two sublayers of any AAL. The CPCS is service-independent and is further divided into the CS and the SAR sublayers. The CPCS is responsible for preparing data for transport across the ATM network, including the creation of the 48-byte payload cells that are passed to the ATM layer. See also AAL, ATM layer, CS, SAR, and SSCS.

2. Telecommunications: call processing control system.


customer premises equipment. Terminating equipment, such as terminals, telephones, and modems, supplied by the telephone company, installed at customer sites, and connected to the telephone company network.


common programming interface for communications. Platform-independent API developed by IBM and used to provide portability in APPC applications. See also APPC.


called party number information element.


See CPP (Combinet Proprietary Protocol) in the "Cisco Systems Terms and Acronyms" section.


cells per second.


custom queuing.

craft interface device

See CID.


A mechanism used by ATM networks when a connection setup request is blocked because a node along a selected path cannot accept the request. In this case, the path is rolled back to an intermediate node, which attempts to discover another path to the final destination using GCAC. See also GCAC.


cyclic redundancy check. Error-checking technique in which the frame recipient calculates a remainder by dividing frame contents by a prime binary divisor and compares the calculated remainder to a value stored in the frame by the sending node.


Corporation for Research and Educational Networking. The result of a merger of BITNET and CSNET. CREN is devoted to providing Internet connectivity to its members, which include the alumni, students, faculty, and other affiliates of participating educational and research institutions, via BITNET III. See also BITNET, BITNET III, and CSNET.


Concentrator Relay Function CRMcell rate margin. One of three link attributes exchanged using PTSPs to determine the available resources of an ATM network. CRM is a measure of the difference between the effective bandwidth allocation per traffic class as the allocation for sustainable cell rate.


certificate revocation list.

cross talk

Interfering energy transferred from one circuit to another.


call reference value. Number carried in all Q.931 (I.451) messages that provides an identifier for each ISDN call.


convergence sublayer. One of the two sublayers of the AAL CPCS, which is responsible for padding and error checking. PDUs passed from the SSCS are appended with an 8-byte trailer (for error checking and other control information) and padded, if necessary, so that the length of the resulting PDU is divisible by 48. These PDUs are then passed to the SAR sublayer of the CPCS for further processing. See also AAL, CPCS, SAR, and SSCS.


Canadian Standards Association. Canadian agency that certifies products that conform to Canadian national safety standards.


Conjugate Structure Algebraic Code Excited Linear Prediction. CELP voice compression algorithm providing 8 Kbps, or 8:1 compression, standardized in ITU-T Recommendation G.729.


called subscriber identification. An identifier whose coding format contains the telephone number from a remote fax terminal.


Compressed Serial Link Internet Protocol. Extension of SLIP that, when appropriate, allows just header information to be sent across a SLIP connection, reducing overhead and increasing packet throughput on SLIP lines. See also SLIP.


call switching module.


carrier sense multiple access collision detect. Media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.


Computer Science Network. Large internetwork consisting primarily of universities, research institutions, and commercial concerns. CSNET merged with BITNET to form CREN. See also BITNET and CREN.


complete sequence number PDU. PDU sent by the designated router in an OSPF network to maintain database synchronization.


channel service unit. Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to together with DSU, as CSU/DSU. See also DSU.


cell transfer delay. In ATM, the elapsed time between a cell exit event at the source UNI and the corresponding cell entry event at the destination UNI for a particular connection. The CTD between the two points is the sum of the total inter-ATM node transmission delay and the total ATM node processing delay.


computer telephony integration. Name given to the merger of traditional telecommunications (PBX) equipment with computers and computer applications. The use of Caller ID to automatically retrieve customer information from a database is an example of a CTI application.


1. Clear To Send. Circuit in the EIA/TIA-232 specification that is activated when DCE is ready to accept data from a DTE.

2. common transport semantic. Cornerstone of the IBM strategy to reduce the number of protocols on networks. CTS provides a single API for developers of network software and enables applications to run over APPN, OSI, and TCP/IP.


coding unit. Type of access device. (See access device.)

Customer Information Control System


customer premises equipment

See CPE.

cut-through packet switching

Packet switching approach that streams data through a switch so that the leading edge of a packet exits the switch at the output port before the packet finishes entering the input port. A device using cut-through packet switching reads, processes, and forwards packets as soon as the destination address is looked up and the outgoing port determined. Also known as on-the-fly packet switching. Compare with store and forward packet switching.


See CxBus (Cisco Extended Bus) in the "Cisco Systems Terms and Acronyms" section.


Term coined by William Gibson in his fantasy novel Neuromancer to describe the "world" of computers and the society that gathers around them. Often used to refer to the Internet, the World Wide Web, or some combination thereof.

cycles per second

See hertz.

cyclic redundancy check

See CRC.

Posted: Tue Sep 21 15:32:12 PDT 1999
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