C


C/N
Difference in amplitude between the desired radio frequency (RF) carrier and the noise in a portion of the spectrum. See carrier-to-noise.
CA
1. certification authority. Entity that issues digital certificates (especially X.509 certificates) and vouches for the binding between the data items in a certificate.
2. Telecommunications: call appearance.
CA certificate
[Digital] certificate for one CA issued by another CA.
cable
Transmission medium of copper wire or optical fiber wrapped in a protective cover.
cable modem
Modulator-demodulator device that is placed at subscriber locations to convey data communications on a cable television system.
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 router
Modular chassis-based router optimized for data-over-CATV hybrid fiber-coaxial (HFC) applications.
cable television
See CATV.
CAC
connection admission control. Set of actions taken by each ATM switch during connection setup to determine whether a connection's requested QoS will violate the QoS guarantees for established connections. CAC also is used when routing a connection request through an ATM network.
caching
A form of replication in which information learned during a previous transaction is used to process later transactions.
CAF
controllable ATM fabric.
cage
A piece of hardware into which cards are installed.
calculated planning impairment factor
See ICPIF.
California Education and Research Federation Network
See CERFnet.
call
An attempted connection between a remote system and LAC, such as a telephone call through the PSTN. An incoming or outgoing call that is established successfully between a remote system and LAC results in a corresponding L2TP session within a previously established tunnel between the LAC and the LNS.
call admission precedence
An MPLS traffic engineering tunnel with a higher priority will, if necessary, preempt an MPLS traffic engineering tunnel with a lower priority. Tunnels that are harder to route are expected to have a higher priority and to be able to preempt tunnels that are easier to route. The assumption is that a lower-priority tunnel can find another path.
call agent
Intelligent entity in an IP telephony network that handles call control in an MGCP model voice over IP network. Also known as a Media Gateway Controller (MGC).
call detail record
See CDR.
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
The time required to establish a switched call between DTE devices.
caller ID
See CLID.
calling line identification
See CLID.
CAM
content-addressable memory. See associative memory. See also CAM in the "Cisco Systems Terms and Acronyms" section.
Canadian Standards Association
See CSA.
CAP
Competitive Access Provider. An 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.
CAR
1. committed access rate. The CAR and DCAR (distributed CAR) services limit the input or output transmission rate on an interface or subinterface based on a flexible set of criteria.
2. Cisco Access Registrar. Provides RADIUS services to DOCSIS modems for the deployment of high-speed data services in a one-way cable plant requiring telco-return for upstream data.
carrier
An 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 Identification Code
See CIC.
carrier sense multiple access collision detect
See CSI.
carrier-to-noise
See C/N.
CAS
channel associated signaling. The transmission of signaling information within the voice channel. CAS signaling often is referred to as robbed-bit signaling because user bandwidth is being robbed by the network for other purposes.
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.
catenet
A network in which hosts are connected to diverse networks, which themselves are connected with routers. The Internet is a prominent example of a catenet.
CATV
cable television. A communication system where multiple channels of programming material are transmitted to homes using broadband coaxial cable. Formerly called Community Antenna Television.
cause codes
Code that indicates the reason for ISDN call failure or completion.
CBAC
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.
CBC
cipher block chaining. Prevents the problems associated with Electronic Codebook (ECB), where every block of "plain text" maps to exactly one block of "cipher text" by having each encrypted block XORed with the previous block of ciphertext. In this way identical patterns in different messages are encrypted differently, depending upon the difference in the previous data.
CBDS
Connectionless Broadband Data Service. European high-speed, packet-switched, datagram-based WAN networking technology. Similar to SMDS. See also SMDS.
CBR
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.
CBWFQ
class-based weighted fair queueing extends the standard WFQ functionality to provide support for user-defined traffic classes.
CC
1. country code. Part of a numbering plan.
2. VCS-call context.
CCB
call control block.
CCIE
See CCIE in the "Cisco Systems Terms and Acronyms" section.
CCITT
Consultative Committee for International Telegraph and Telephone. International organization responsible for the development of communications standards. Now called the ITU-T. See also ITU-T.
CCN unit
continuous control node unit. Provides communication between the redundant sides of the admin shelf.
CCNA
Cisco Certified Network Associate.
CCO
See CCO in the "Cisco Systems Terms and Acronyms" section.
CCOT
cross office transfer time.
CCR
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.
CCS
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.
CCSRC
See CCSRC in the "Cisco Systems Terms and Acronyms" section.
CCSS7
Common Channel Signaling System 7. Protocol used by the AT&T signaling network. The ICM's NIC receives routing requests from the CCSS7 network and returns a routing label to the CCSS7 network.
CD
Carrier Detect. A signal that indicates whether an interface is active. Also, a signal generated by a modem indicating that a call has been connected.
CDB
call detail block. Consists of several Call Data Elements. The CDB is generated at a Certain Point in Call (PIC). For example, a CDB is generated when the call is answered, released, and so on.
CDDI
Copper Distributed Data Interface. The 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.
CDE
call detail element. A data element that includes a basic information field within a billing record. Examples of a CDE are the calling number, the called number, and so on.
CDF
channel definition format. Technology for "push" applications on the World Wide Web. CDF is an application of XML. See also XML.
CDMA
code division multiple access. A method of dividing a radio spectrum to be shared by multiple users through the assignment of unique codes. CDMA implements spread spectrum transmission.
CDP
See CDP (Cisco Discovery Protocol) in the "Cisco Systems Terms and Acronyms" chapter.
CDPD
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.
CDR
call detail record.
1. A record written to a database for use in postprocessing activities. CDR files consist of several CDBs. These activities include many functions, but primarily are billing and network analysis. Cisco CallManager writes CDR records to the SQL database as calls are made in a manner consistent with the configuration of each individual Cisco CallManager.
2. Used in the original telephony networks, and now extended to mobile wireless network calls, the CDR contains billing information for charging purposes. In a GPRS network, the charging gateway sends the billing information within a CDR to the network service provider for that subscriber.
3. VNS record of voice or data SVCs, which includes calling and called numbers, local and remote node names, data and time stamp, elapsed time, and Call Failure Class fields.
4. Wireless—Used in the original telephony networks and now extended to mobile wireless network calls. The CDR contains billing information for charging purposes. In a GPRS network, the charging gateway sends the billing information within a CDR to the network service provider for that subscriber.
CD-ROM
compact disc read-only memory.
CD-RW
compact disc read/write.
CDV
cell delay variation. A 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.
CDVT
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.
CE router
customer edge router. A router that is part of a customer network and that interfaces to a provider edge (PE) router.
CED
caller-entered digits. Digits entered by a caller on a touch-tone phone in response to prompts. Either a peripheral (ACD, PBX, or VRU) or the carrier network can prompt for CEDs.
CEF
See CEF in the "Cisco Systems Terms and Acronyms" section.
cell
The 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
See CDVT.
cell loss priority
See CLP.
cell loss ratio
See CLR.
cell payload scrambling
A 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.
cell transfer delay
See CTD.
cells per second
Abbreviated cps.
Cellular Digital Packet Data
See CDPD.
cellular radio
Technology that uses radio transmissions to access telephone-company networks. Service is provided in a particular area by a low-power transmitter.
CELP
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.
CEN
European Committee for Standardization. CEN's mission is to promote voluntary technical harmonization in Europe in conjunction with worldwide bodies and its partners in Europe. The organization works in partnership with CENELEC and ETSI (European Telecommunications Standards Institute).
CENELEC
Comite Europeen de Normalisation Electrotechnique. CENELEC is the European Committee for Electrotechnical Standardization. It was set up in 1973 and was officially recognised as the European Standards Organisation in its field by the European Commission in Directive 83/189 EEC. CENELEC works with 40,000 technical experts from 19 EC and EFTA countries to publish standards for the European market.
central office
See CO.
Centrex
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 CC and LEC.
CEP
Certificate Enrollment Protocol. Certificate management protocol jointly developed by Cisco Systems and VeriSign, Inc. CEP is an early implementation of Certificate Request Syntax (CRS), a standard proposed to the Internet Engineering Task Force (IETF). CEP specifies how a device communicates with a CA, including how to retrieve the public key of the CA, how to enroll a device with the CA, and how to retrieve a certificate revocation list (CRL). CEP uses Public Key Cryptography Standard (PKCS) 7 and PKCS 10 as key component technologies. The public key infrastructure working group (PKIX) of the IETF is working to standardize a protocol for these functions, either CRS or an equivalent. When an IETF standard is stable, Cisco will add support for it.
CEPT
Conf�rence Europ�enne des Postes et des T�l�communications. Association of the 26 European PTTs that recommends communication specifications to the ITU-T.
CER
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.
CERFnet
California Education and Research Federation Network. TCP/IP network, based in Southern California, that connects hundreds of higher-education centers inter- nationally 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.
CERN
European Laboratory for Particle Physics. Birthplace of the World Wide Web.
CERT
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. Regional CERTs are, like NICs, springing up in different parts of the world.
certificate
Digital representation of user or device attributes, including a public key, that is signed with an authoritative private key.
CES
circuit emulation service. Enables users to multiplex or to 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.
CET
See CET in the "Cisco Systems Terms and Acronyms" section.
CFRAD
See Cisco FRAD in the "Cisco Systems Terms and Acronyms" section.
CGI
Common Gateway Interface. A 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.
chaining
An SNA concept in which RUs are grouped together for the purpose of error recovery.
Challenge Handshake Authentication Protocol
See CHAP.
channel
1. Communication path wide enough to permit a single RF transmission. 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.
channel definition format.
See CDF.
Channel Interface Processor
See CIP in the "Cisco Systems Terms and Acronyms" section.
channel service unit
See CSU.
channel-attached
Pertaining to the 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.
CHAP
Challenge Handshake Authentication Protocol. Security feature supported on lines using PPP encapsulation that prevents unauthorized access. CHAP does not itself prevent unauthorized access, but merely identifies the remote end. The router or access server then determines whether that user is allowed access. Compare with PAP.
chargen
Character Generation. Via TCP, a service that sends a continual stream of characters until stopped by the client. Via UDP, the server sends a random number of characters each time the client sends a datagram.
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.
Cheapernet
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, EtherChannel, and IEEE 802.3.
checksum
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 is 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.
churn
Many subscriber additions and deletions.
CIA
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.
CIC
Prefix to select different long distance carriers; prefixes to select tielines, trunk groups, and WATS lines; and private number plans, such as seven-digit dialing.
CICNet
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.
CICS
Customer Information Control System. IBM application subsystem allowing transactions entered at remote terminals to be processed concurrently by user applications.
CID
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.
CIDR
classless interdomain routing. Technique supported by BGP4 and based on route aggregation. CIDR allows routers to group routes together to reduce 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 four octets, separated by periods, followed by a forward slash and a two-digit number that represents the subnet mask. See also BGP4.
CIP
See CIP (Channel Interface Processor) in the "Cisco Systems Terms and Acronyms" section.
Cipher
Cryptographic algorithm for encryption and decryption.
ciphertext
Data that has been transformed by encryption so that its semantic information content (that is, its meaning) is no longer intelligible or directly available.
CIR
committed information rate. The 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.
circuit
A communications path between two or more points.
circuit group
A 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
The switching system in which a dedicated physical circuit path must exist between the sender and the 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.
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.
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.
CiscoBus controller
See SP in the "Cisco Systems Terms and Acronyms" section.
CiscoFusion
See CiscoFusion in the "Cisco Systems Terms and Acronyms" section.
Cisco Network Registrar
A software product that provides IP addresses, configuration parameters, and DNS names to DOCSIS cable modems and PCs, based on network and service policies. CNR also provides enhanced TFTP server capabilities, including the generation of DOCSIS cable modem configuration files.
Cisco Optical Network Planner
See Cisco Optical Network Planner 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.
CiscoView
See Cisco-trunk (private line) call in the "Cisco Systems Terms and Acronyms" section.
Cisco Wavelength Router Manager
See Cisco Wavelength Router Manager in the "Cisco Systems Terms and Acronyms" section.
Cisco WRM
See Cisco WRM in the "Cisco Systems Terms and Acronyms" section.
Cisco WW TAC
See Cisco WW TAC in the "Cisco Systems Terms and Acronyms" section.
C-ISUP
See C-ISUP in the "Cisco Systems Terms and Acronyms" section. See also ISUP.
CIX
Commercial Internet Exchange. A connection point between the commercial Internet service providers. Pronounced "kicks." See also FIX and GIX.
CKTINT
Circuit Interworking software. A module in the SS7 application software that translates SS7 signals for the Cisco VCO/4K and host applications. It also performs call processing and circuit maintenance tasks.
Class A station
See DAS.
Class B station
See SAS.
Class of Restrictions
See COR.
class of service
See CoS.
classical IP over ATM
See CIA.
classless interdomain routing
See CIDR.
CLAW
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 the efficiency of channel use and allows the CIP to provide the functionality of a 3172 in TCP/IP environments and to 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
A channel that uses out-of-band signaling (as opposed to in-band signaling), so the channel's entire bit rate is available.
Clear To Send
See CTS.
ClearDDTS
Distributed Defect Tracking System. Development engineers and CSEs use ClearDDTS (Rational) to track bugs for software, hardware, and microcode products. CSEs also use ClearDDTS as a formal way to escalate an issue to developers. Customers use Release Note information derived from the ClearDDTS database to troubleshoot problems or to select a software version for an upgrade.
CLEC
competitive local exchange carrier. A company that builds and operates communication networks in metropolitan areas and provides its customers with an alternative to the local telephone company. See also CAF.
CLEI
Common Language Equipment Identifier. The standard code used by suppliers to identify equipment parts and system configurations. CLEIis a registered trademark of Bellcore (now Telcordia).
CLI
1. command-line interface. An 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. The basic Cisco IOS configuration and management interface.
CLID
calling line ID. Information about the billing telephone number from which a call originated. The CLID value might be the entire phone number, the area code, or the area code plus the local exchange. Also known as Caller ID.
client
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 RFC.
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.
CLNP
Connectionless Network Protocol. The OSI network layer protocol that does not require a circuit to be established before data is transmitted. See also CLNS.
CLNS
Connectionless Network Service. The 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.
cloning
Creating and configuring a virtual access interface by applying a specific virtual template interface. The template is the source of the generic user information and the router-dependent information. The result of cloning is a virtual access interface configured with all the commands in the template.
CLP
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 to free up resources to handle insured traffic.
CLR
cell loss ratio. In ATM, the ratio of discarded cells to cells that are transmitted successfully. CLR can be set as a QoS parameter when a connection is set up.
CLTP
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. It is 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, it's an IBM 3174 or 3274 device.
CM
cable modem. Device used to connect a PC to a local cable TV line and receive data at much higher rates than ordinary telephone modems or ISDN. A cable modem can be added to or integrated with a set-top box, thereby enabling Internet access via a television set. In most cases, cable modems are furnished as part of the cable access service and are not purchased directly and installed by the subscriber.
CMI
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.
CMIP
Common Management Information Protocol. OSI network management protocol created and standardized by ISO for the monitoring and control of heterogeneous networks. See also CMIS.
CMIS
Common Management Information Services. OSI network management service interface created and standardized by ISO for the monitoring and the control of heterogeneous networks. See also CMIP.
CMNS
Connection-Mode Network Service. Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring). See also CONP.
CMNM
See CMNM in the "Cisco Systems Terms and Acronyms" section.
CMS
1. call management system. A reporting package used on ACDs and PBXs made by Lucent.
2. configuration management system. An application that controls and monitors the Sun Netra ft 1800 hardware
CMT
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.
CMTS
A cable modem termination system, such as a router or a bridge, typically located at the cable headend. Any DOCSIS-compliant headend cable router, such as the Cisco uBR7246.
CNS/AD
Cisco Networking Services for Active Directory, which consists of a port of Active Directory to Solaris and HP/UX, and an NT and UNIX client implementation of the LDAP API and GSS-API.
CO
central office.The local telephone company office to which all local loops in a given area connect and in which circuit switching of subscriber lines occurs.
CO FRAD
central office frame relay access device.
coaxial cable
Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. Two types of coaxial cable currently are 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.
codec
coder-decoder. 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.
coder-decoder
See codec.
coding
Electrical techniques used to convey binary signals.
coding violation
See CV.
CO-IPX
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.
collision
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.
COM
common equipment. Items used by more than one channel or equipment function.
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 Language Equipment Identifier
See CLEI.
Common Link Access for Workstations
See CLAW.
Common Management Information Protocol
See CMIP.
Common Management Information Services
See CMIS.
common part convergence sublayer
See CPCS.
Common Programming Interface for Communications
See CPI-C.
common transport semantic
See CTS.
communication
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 a 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.
community
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.
companding
Contraction derived from the opposite processes of compression and expansion. Part of the PCM process whereby analog signal values are rounded logically to discrete scale-step values on a nonlinear scale. The decimal step number then is 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
See CSNP.
composite clock
A bipolar timing signal containing 64 khz bit-clock and 8 khz byte-clock frequencies (also called composite timing).
compound option
A DOCSIS option that is composed of a number of suboptions. For example, options 4 and 24 are compound options.
Compressed Serial Link Internet Protocol
See CSI.
compression
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 CSNET.
concentrator
See hub.
CONF
configuration failure. Resource is OOS because its provisioning information is inconsistent.
Conf�rence Europ�enne des Postes et des T�l�communications
See CEPT.
configuration direct VCC
In ATM, a bi-directional point-to-point VCC set up by an 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 the 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.
congestion
Traffic in excess of network capacity.
congestion avoidance
Mechanism by which an ATM network controls the traffic entering the network to minimize delays. 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.
connection management
See CMT.
connectionless
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
See CBDS.
Connectionless Network Protocol
See CLNP.
Connectionless Network Service
See CLNS.
Connection-Mode Network Service
See CMNS.
connection-oriented
Term used to describe data transfer that requires the establishment of a virtual circuit. See also connectionless and virtual circuit.
Connection-Oriented Network Protocol
See CONP.
CONP
Connection-Oriented Network Protocol. OSI protocol providing connection-oriented operation to upper-layer protocols. See also CMNS.
CONS
connection-oriented network service.
console
DTE through which commands are entered into a host.
constant bit rate
See CBR.
constraint-based routing
Procedures and protocols that determine a route across a backbone take into account resource requirements and resource availability instead of simply using the shortest path.
Consultative Committee for International Telegraph and Telephone
See CCITT.
content-addressable memory
See associative memory.
contention
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 CBAC.
control direct VCC
In ATM, a bidirectional VCC set up by an LEC to an LES. One of three control connections defined by Phase 1 LANE. Compare with configuration direct VCC and control direct VCC.
control distribute VCC
In ATM, a unidirectional VCC set up from an LES to an 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 messages
Signalling messages that provide the control of setup, maintenance, and teardown of L2TP sessions and tunnels.
control point
See CP.
control signal distribution box
See CSD box.
convergence
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.
conversation
In SNA, an LU 6.2 session between two transaction programs.
cookie
A 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
See COSINE.
COOS
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
See CDDI.
COPS
Common Open Policy Service. Quality of service (QoS) policy exchange protocol proposed as an IETF standard for communicating network QoS policy information.
COR
Functionality that provides the capability to deny certain call attempts based on the incoming and outgoing class of restrictions provisioned on the dial peers. This functionality provides flexibility in network design, allows users to block calls (for example, to 900 numbers), and applies different restrictions to call attempts from different originators. COR specifies which incoming dial peer can use which outgoing dial peer to make a call.
CORBA
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 also 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
See CREN.
CoS
class of service. An 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.
COS
Corporation for Open Systems. Organization that promulgates the use of OSI protocols through conformance testing, certification, and related activities.
COSINE
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.
cost
An 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. Routing protocols use cost values 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.
COT
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.
CP
1. control point. In SNA networks, an 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 can communicate with logically adjacent CPs by way of CP-to-CP sessions. See also EN and NN.
2. Telecommunications: control processor.
CPC
calling party category.
CPCS
1. common part convergence sublayer. One of the two sublayers of any AAL. The CPCS is service-independent and is divided further into the CS sublayer and the SAR sublayer. 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.
CPE
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. Can also refer to any telephone equipment residing on the customer site.
CPI-C
common programming interface for communications. Platform-independent API developed by IBM and used to provide portability in APPC applications. See also APPC.
CPNIE
called party number information element.
CPP
See CPP (Combinet Proprietary Protocol) in the "Cisco Systems Terms and Acronyms" section.
cps
cells per second. Unit of measure used for ATM switch volumes.
CQ
custom queuing.
craft interface device
See CID.
crankback
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.
CRC
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.
CREN
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, the students, the faculty, and other affiliates of participating educational and research institutions, via BITNET III. See also BITNET, BITNET III, and CSNET.
CRF
Concentrator Relay Function CRM cell 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.
CRL
certificate revocation list. Data structure that enumerates digital certificates that have been invalidated by their issuer prior to when they were scheduled to expire.
cross talk
Interfering energy transferred from one circuit to another.
CRP
customer routing point. AT&T's terminology for third-party processors that accept routing requests from the CCSS7 network. Within the ICM, the Network Interface Controller (NIC) acts as a CRP.
CRV
call reference value. Number carried in all Q.931 (I.451) messages that provides an identifier for each ISDN call.
cryptographic algorithm
Algorithm that employs the science of cryptography, including encryption algorithms, cryptographic hash algorithms, digital signature algorithms, and key agreement algorithms.
cryptographic key
Usually shortened to just "key." Input parameter that varies the transformation performed by a cryptographic algorithm.
CS
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 are padded, if necessary, so that the length of the resulting PDU is divisible by 48. These PDUs then are passed to the SAR sublayer of the CPCS for further processing. See also AAL, CPCS, SAR, and SSCS.
CSA
Canadian Standards Association. Canadian agency that certifies products that conform to Canadian national safety standards.
CS-ACELP
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.
CSD box
control signal distribution box. Bulkhead splitter box that distributes the clock and control system signals within a system.
CSFS
customer support forwarding service. Facility within the ICM Logger that receives events from all parts of the ICM, filters them, and saves the appropriate messages. The Data Transfer Process (DTP) sends these messages to Cisco Customer Support.
CSI
called subscriber identification. An identifier whose coding format contains the telephone number from a remote fax terminal.
CSLIP
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.
CSM
1. call switching module.
2. See CSM in the "Cisco Systems Terms and Acronyms" section.
CSMA/CD
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. Ethernet and IEEE 802.3 use CSMA/CD access.
CSNET
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.
CSNP
complete sequence number PDU. PDU sent by the designated router in an OSPF network to maintain database synchronization.
CSO
composite second order beat. Peak of the average level of distortion products due to second-order non-linearities in cable system equipment.
CSU
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.
CSV
comma separated values. Commonly used no-frills text file format used for import from and import to spreadsheets and SQL databases.
CTB
composite triple beat. Peak of the average level of distortion components due to third-order non-linearities in cable system equipment.
CTD
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.
CTI
computer telephony integration. The name given to the merger of traditional telecommunications (PBX) equipment with computers and computer applications. The use of caller ID to retrieve customer information automatically from a database is an example of a CTI application.
CTS
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.
CU
coding unit. A type of access device. See also access device.
Customer Information Control System
See CICS.
customer premises equipment
See CPE.
cut-through packet switching
A packet switching approach that streams data through a switch so 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 is determined. Also known as on-the-fly packet switching. Compare with store and forward packet switching.
CWAF
See CWAF in the "Cisco Systems Terms and Acronyms" section.
CV
coding violation. Occurrence of transmission bit error(s) in paths and lines, as detected by examining a redundancy check code embedded within the signal format. CV also refers to the performance parameter, which is the count of transmission error detections at line, path, and section levels.
CxBus
See CxBus (Cisco Extended Bus) in the "Cisco Systems Terms and Acronyms" section.
Cyberspace
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.

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