C

C7 (Common Channel Signaling 7)

A signaling protocol specified by the ITU-T and used in high-speed digital networks to provide communication between intelligent network nodes. C7 is the European equivalent of SS7. Also sometimes called CCS7, for Common Channel Signaling System 7.

C (cross) link

A link that interconnects mated STPs.

CA (Certificate Authority)

A trusted third-party organization that issues digital certificates used to create digital signatures and publicprivate key pairs. The CA guarantees that the individual granted the unique certificate is, in fact, who he or she claims to be.

cable modem

A device designed to operate over cable TV networks to provide high-speed access to the Internet.

CableHome

A CableLabs HAN standard. The CableHome 1.1 specification includes gateway security features; standardized prioritized QoS for HANs; support for home servers, teleworkers, and home offices; simple parental control; and LAN management messaging and LAN IP statistics monitoring.

CableLabs

A nonprofit research and development consortium that is dedicated to helping its cable operator members integrate new cable telecommunications technologies into their business objectives. CableLabs has developed industry specifications such as DOCSIS, OpenCable, PacketCable, VOD Metadata, and CableHome.

call processing

A sequence of operations performed by a switching system from the acceptance of an incoming call through the final disposition of the call.

campus network

A network that connects LANs from multiple departments in a single building or campus. Campus networks are LANs; although they may span several miles, they do not include WAN services.

CAP (Carrierless Amplitude Phase Modulation)

A single-carrier modulation scheme used in early deployments of ADSL.

carrier frequency

The frequency of the carrier wave that is modulated to transmit signals.

carrier system

A means of obtaining a number of channels over a single path by modulating each channel on a different carrier frequency and demodulating at the receiving point to restore the signals to their original frequency.

Cat 1 (Category 1) UTP

An EIA/TIA 568 standard for commercial building telecommunications wiring. This old-style UTP telephone cable is unsuitable for data transmission.

Cat 2 (Category 2) UTP

An EIA/TIA 568 standard of cable that can be used for data rates up to 4Mbps.

Cat 3 (Category 3) UTP

An EIA/TIA 568 standard of cable that can be used for data rates up to 10Mbps. This is the minimum cable requirement for 10BASE-T.

Cat 4 (Category 4) UTP

An EIA/TIA 568 standard of cable that can be used as the lowest-grade UTP, acceptable for data rates up to 16Mbps (token ring).

Cat 5 (Category 5) UTP

An EIA/TIA 568 standard of cable that can be used for data rates up to 100Mbps.

Cat 5e (Category 5e) UTP

An EIA/TIA 568 standard of cable that provides performance of up to 125MHz and is frequently used for 1000BASE-T Gigabit Ethernet.

Cat 6 (Category 6) UTP

An EIA/TIA 568 standard of cable that provides performance of up to 400MHz, more than double that of Category 5 and 5e, and is used for 10BASE-T/100BASE-TX and 1000BASE-T (Gigabit Ethernet) connections.

Cat 7 (Category 7) UTP

An emerging category of cable that is expected to operate up to 600MHz and will use STP or ScTP.

CATV (Community Antenna Television)

Signals that can be received at a selected site by sensitive, directional antennas and then transmitted to subscribers via a cable network. Additional channels, not normally available in that area, can also be transmitted. Traditional analog CATV is based on RF transmission, generally using 75-ohm coaxial cable as the transmission medium. CATV offers multiple frequency-divided channels, allowing mixed transmissions to be carried simultaneously.

C-band

A portion of the electromagnetic spectrum, approximately 4GHz to 6GHz, that is used primarily for satellite and microwave transmission.

CBQ (Class-Based Queuing)

A fully open, nonproprietary technology that brings bandwidth-controlled CoS to IP network infrastructures. It allows traffic to be prioritized according to IP application type, IP address, protocol type, and other variables. It allocates unused bandwidth more effectively than other QoS mechanisms do, and it uses priority tables to give critical applications the most immediate access to unused bandwidth.

CBR (Constant Bit Rate)

The highest ATM service class. CBR provides a constant, guaranteed rate to real-time applications such as streaming video, providing continuous bandwidth. It emulates a circuit-switched approach and is associated with minimum latencies and losses.

CCITT (Comité Consultatif International de Téléphonie et de Télégraphie)

An advisory committee to the ITU whose recommendations covering telecommunications have international influence among engineers, manufacturers, and administrators. It is now known as the ITU-T.

CCK (Complementary Code Keying)

A modulation scheme used with 802.11b WLANs. CCK was adopted to replace the Barker Code in wireless digital networks.

CCS (Common-Channel Signaling)

An electronic means of signaling between two switching systems, independent of the voice path. The use of CCS makes possible new customer services, versatile network features, more flexible call routing, and faster connections.

CDDI (Copper-Distributed Data Interface)

A version of FDDI that runs on UTP cable rather than on fiber-optic cable.

CDM (Code Division Multiplexing)

A form of multiplexing that encodes data with a special code associated with each channel and uses the constructive interference properties of the special codes to perform the multiplexing.

CDMA (Code Division Multiple Access)

A digital cellular technology that uses spread spectrum techniques. With CDMA, every channel uses the full available spectrum, and individual conversations are encoded with a pseudorandom digital sequence or frequency-hopping schedule.

CDMA2000

A family of 3G mobile standards that use CDMA to send voice, data, and signaling data between mobile phones and cell sites. CDMA2000 devices include color displays, GPS, digital and video cameras, push-to-talk, support for streaming-type real-time VOD/audio-on-demand services, and voice recognition functions. Also known as IMT-2000 CDMA Multi-Carrier (CDMA-MC).

CDMA450

A TIA/EIA-IS-CDMA2000 (CDMA-MC) system deployed at 450MHz. CDMA450 provides a larger cell size compared to other bands, which translates to fewer cell sites and significantly lower capital and operating expenditures to service vast coverage areas.

cdmaOne

A 2G CDMA technology (IS-95) that offers data rates of 9.6Kbps to 14.4Kbps. cdmaOne describes a complete wireless system based on the TIA/EIA IS-95 CDMA standard and represents the end-to-end wireless system and all the necessary specifications that govern its operation. cdmaOne provides a family of related services, including cellular, PCS, and wireless local loop.

CDPD (Cellular Digital Packet Data)

A North American standard for transferring packet data over cellular phone channels.

CD-ROM (Compact DiscRead Only Memory)

A storage device that is used in computer systems and typically contains multimedia information.

cell

A fixed-length packet.

cell relay

A form of packet transmission used by ATM networks. Cell relay transmits 53 octet fixed-length packets over a packet-switched network. Because the cells are tiny and of fixed length, they can be processed and switched at very high speeds. ATM makes it possible to use a single transmission scheme for voice, data, and video traffic on LANs and WANs.

cellular

A communication service in which voice or data is transmitted by radio frequencies. The service area is divided into cells, each served by a transmitter. The cells are connected to a mobile switching exchange, which is connected to the worldwide telephone network.

CELP (Code-Excited Linear Prediction)

A vector-quantization-based compression scheme for speech. CELP can compress speech down to 4.8Kbps. There is also a low-end variant called LPC.

centrex

A local exchange carrier service in which switching occurs at a local exchange rather than at customer-owned PBXs. The telephone company owns and manages all the communications equipment.

CEPT (Conférence Européenne des Administrations des Postes et des Télecommunications [European Conference of Postal and Telecommunications Administrations])

An organization formed by the European PTTs for the discussion of operational and tariff matters. CEPT-0 (or E-0) is the basic increment, and it operates at 64Kbps. CEPT-1 is a 2.048Mbps 32-channel circuit; CEPT-2 is an 8.488Mbps 128-channel circuit; CEPT-3 is a 34.368Mbps 512-channel circuit; CEPT-4 is a 139.246Mbps 2,048-channel circuit; CEPT-5 is a 565.148Mbps 8,192-channel circuit.

CERN (Conseil Européen pour la Recherche Nucléaire [European Organization for Nuclear Research])

The world's largest particle physics laboratory and the birthplace of the World Wide Web.

channel

A logical conversation path. A channel is the frequency band, time slot, or wavelength (also referred to as lambda) over which a given conversation flows.

channel bank

Equipment typically used in a telephone exchange that performs multiplexing of lower-speed, digital channels into a higher-speed composite channel. The channel bank also detects and transmits signaling information for each channel and transmits framing information so that time slots allocated to each channel can be identified by the receiver.

channel capacity

The maximum data traffic that a channel can handle.

CHAP (Challenge Handshake Authentication Protocol)

A protocol that uses a three-way handshake to periodically verify the identity of the peer throughout the life of the connection. The server sends to the remote workstation a random token that is encrypted with the user's password and sent back to the server. The server performs a lookup to see if it recognizes the password. If the values match, the authentication is acknowledged; if not, the connection is terminated. A different token is provided each time a remote user dials in, which provides additional robustness.

chirped-pulse WDM

A Bell Labs system in which a specialized mode-locked laser rapidly emits very wide pulses of light. Because each part of a fiber interacts differently with varying frequencies of light, the result of chirped-pulse WDM is unequal dispersion. The pulse is stretched out when it enters the fiber, and data can be put on the discrete frequencies that emerge.

CIDR (Classless Interdomain Routing)

An IP addressing scheme that replaces the older system based on Classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses. The CIDR addressing scheme is hierarchical. Large national and regional service providers are allocated large blocks of contiguous Internet addresses, which they then allocate to other smaller ISPs or directly to organizations. Networks can be divided into subnetworks, and networks can be combined into supernetworks, as long as they share a common network prefix.

CIR (Committed Information Rate)

The amount of bandwidth that a user can expect from a Frame Relay carrier on a particular virtual circuit.

circuit

The physical path that runs between two or more points that can be used for two-way communication or to perform another specific function.

circuit grade

The data-carrying capability of a circuit. The grades of circuit are broadband, voice, subvoice, and telegraph.

circuit switching

The temporary direct connection of two or more channels between two or more points in order to provide the user with exclusive use of an open channel with which to exchange information. A discrete circuit path is set up between the incoming and outgoing lines, in contrast to message switching and packet switching, in which no such physical path is established.

cladding

In fiber-optic cable, a low-refractive-index material that surrounds the core and provides optical insulation and protection to the core.

clear-forward/clear-back signal

A signal transmitted from one end of a subscriber line or trunk, in the forward/backward direction, to indicate at the other end that the established connection should be disconnected. Also called a disconnect signal.

CLEC (Competitive Local Exchange Carrier)

A telephone company that competes with an ILEC. CLECs in the United States today focus mainly on delivering dial tone to business customers.

client

A computer that requests network or application services from a server. A client has only one user; a server is shared by many users.

client/server model

The model of interaction in a distributed system in which a program at one site sends a request to a program at another site and awaits a response. The requesting program is called a client; the program satisfying the request is called the server.

CLNP (Connectionless Network Protocol)

The OSI protocol for OSI connectionless network service. CLNP is the OSI equivalent to IP.

clocking

The use of clock pulses to control synchronization of data and control characters.

closed user group

A group of users in a network who are permitted to communicate with each other but not with users outside the group.

cluster

Two or more terminals connected to a single point or node.

cluster controller

A device that handles the remote communications processing for multiple (usually dumb) terminals or workstations.

CMIP (Common Management Information Protocol)

The OSI management information protocol for network management. CMIP is an alternative to SNMP and is not widely implemented.

CMIS (Common Management Information Services)

A service interface created and standardized by the ISO for managing heterogeneous networks.

CMTS (Cable Modem Termination System)

A device on which coax trunks terminate. CMTSs are linked by a common Ethernet hub, which, in turn, feeds into the IP router, which then develops the optimum path to take over an optical backbone onto the ISP.

CO (Central Office)

The physical location where local service providers terminate subscriber lines and locate the switching equipment that interconnects those lines. CO is used as a term in North America; elsewhere in the world, it is also referred to as a local exchange or Class 5 office.

coax (coaxial cable)

A transmission medium that consists of one (sometimes more) central wire conductor, surrounded by a dielectric insulator and encased in either a wire mesh or extruded metal sheathing. There are many varieties of coax, depending on the degree of EMI shielding afforded, voltages, and frequencies accommodated.

code

The conventions that specify how data may be presented in a particular system.

code character

A set of conventional elements established by code to enable the transmission of a written character (letter, figure, punctuation sign, arithmetical sign, and so on) or the control of a particular function (spacing, shift, line-feed, carriage return, phase corrections, and so on).

codec (coder-decoder)

A device used to convert analog signals, such as speech, music, or television, to digital form for transmission over a digital medium and back again to the original analog form. One codec is required at each end of a channel.

coding scheme

A pattern of bits used to represent the characters in a character set, as well as carriage returns and other keyboard functions. Examples of coding schemes are ASCII, EBCDIC, and Unicode.

COFDM (Coded Orthogonal Frequency Division Multiplexing)

A complex technique that combines OFDM with error-correcting codes, adaptive equalization, and reconfigurable modulation to provide many beneficial properties, including resistance to multipath, phase distortion, fading, and burst noise. COFDM is used in Europe and other places where the DAB standard has been adopted for digital radio broadcasting and for terrestrial DTV. It is also used in ADSL transmission.

collision

Overlapping transmissions that interfere with one another. A collision occurs when two or more devices attempt to transmit at or about the same instant.

collision domain

A small cluster in a LAN where collisions occur. Collision domains are used to reduce collisions throughout a network.

command

A signal or group of signals that cause a computer to execute an operation or series of operations.

command-driven

Programs requiring that the task to be performed be described in a special language with strict adherence to syntax.

common-battery signaling

A method by which supervisory and telephone address information is sent to an exchange by depressing and releasing the switch on the cradle of the handset.

common carrier

An organization in the business of providing regulated telephone, telegraph, Telex, and data communications services.

common control

An automatic switching arrangement in which the control equipment necessary for the establishment of connections is shared and is associated with a given call only during the period required to accomplish the control function.

communication adapter

A hardware feature that permits telecommunication lines to be attached to the processor.

communication line

A link (e.g., wire, telephone circuit, microwave, satellite) used to transmit data between computers and/or remote devices.

communications controller

(1) A hardware device for attaching either communication lines, ASCII devices, or a LAN to the processing unit. (2) A dedicated device with special processing capabilities for organizing and checking data and handling information traffic to and from many remote terminals or computers, including functions such as message switching. Also called a communications processor.

communications satellite

A satellite designed to act as a telecommunications radio relay and usually positioned in geosynchronous orbit 23,000 miles (35,800 km) above the equator so that it appears from earth to be stationary.

compander

A compressor at one point in a communications path for reducing the volume range of signals, followed by an expander at another point for restoring the original volume range. A compander is designed to improve the ratio of the signal to the interference entering in the path between the compressor and expander.

compression

The application of any of several techniques to reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.

compressor

An electronic device that compresses the volume range of a signal.

concatenation

(1) The linking of transmission channels (e.g., phone lines, coaxial cable, optical fiber) end to end. (2) The linking of SONET STS-1 frames in order to carry a broadband information stream.

concentrator

A device that connects a number of circuits that are not all used at once to a smaller group of circuits for economical transmission. A telephone concentrator achieves the reduction with a circuit-switching mechanism. In data communications, a multiport repeater or hub brings together the connections from multiple network nodes. Concentrators have moved past their origins as wire concentration centers and often include bridging, routing, and management devices.

conditioning

A procedure for making transmission impairments of a circuit lie within certain specified limits, typically used on telephone lines leased for data transmission to improve the possible transmission speed. Two types are used: C conditioning and D conditioning. Also called line conditioning.

configuration

The devices and programs that make up a system, subsystem, or network. The term configuration may refer to a hardware configuration or a software configuration.

configure

To describe to the system the devices and optional features installed on the system and describe their utilization.

connect time

The amount of time that a circuit, typically in a circuit-switched environment, is in use.

connectionless network

A network that treats each packet or datagram as a separate entity that contains the source and destination address. Connectionless services can drop packets or deliver them out of sequence, based on encountering various network conditions, such as congestion or outages.

connection-oriented network

A network in which the connection setup is performed before information transfer occurs. The path is conceived at the outset, and after the path is determined, all the subsequent information follows the same path to the destination. In a connection-oriented network, there can be some delay up front, while the connection is being set up, but because the path is predetermined, there is no delay at intermediate nodes after the connection is set up.

connectivity

A term used to describe the physical interconnections of multiple devices/ computers/networks employing similar or different technology and/or architecture together to accomplish effective communication between and among connected members involving data exchange and/or resource sharing.

contactless identification

A technology in which a smart card has an antenna embedded inside it, enabling communication with a card reader without physical contact. The chip on the smart card stores data and programs that are protected by advanced security features. Contactless smart cards are passed near an antenna, or reader, to carry out a transaction.

content delivery network

A network with delivery services that are structured specifically for a client and are focused on streaming audio, video, and media, as well as the supporting e-commerce applications.

contention

A method of line control in which the terminals request permission to transmit. If the channel in question is free, transmission proceeds; if it is not free, the terminal has to wait until it becomes free. A computer can build up a queue of contention requests; this queue can be organized in a prearranged sequence or in the sequence in which requests are made.

control character

A character inserted into a data stream for signaling the receiving station to perform a function to identify the structure of the message. Newer protocols use bit-oriented control procedures.

control network

A type of HAN network for home automation and control that is typically a low-speed powerline network. Control networks have relatively low cost and simple implementation, but they are not designed to support real-time, high-bandwidth, or mobility requirements.

control plane

An operational part of a network, including infrastructure and distributed intelligence, that executes various signaling, routing, and other control protocols (e.g., OSPF, RIP, RSVP). The control plane protocols exchange data with their peers and generate control information such as routing tables that is needed to forward data packets. Additional functions include managing user interfaces and monitoring system status and health.

control station

The station in a point-to-point or multipoint network that controls the sending and receiving of data. This station can poll or address tributary stations.

control unit

Circuitry or a device used to coordinate and control the operation of one or more I/O or storage devices and to synchronize the operation of such devices with the operation of the computer system as a whole.

controlled access unit

A managed MAU or a managed multiport siring hub for token-ring networks.

convergence

The trend for multiple network technologies and products to come together to form one network with the advantages of all the technologies and products, reducing costs and simplifying operations, administration, and management. In telecommunications, convergence can refer to network infrastructure convergence, device convergence, and applications convergence.

conversion

The process of changing from one method to another. It may refer to changing processing methods, data, or systems.

COPS (Common Open Policy Service)

An IETF query/response-based client/server protocol for supporting policy control. It addresses how servers and clients on a network exchange policy information, and it transmits information between a policy server and its clients, which are policy-aware devices such as switches.

core

The central part of a network.

CoS (Class of Service)

A categorization of subscribers or traffic according to priority levels. Network resources are allocated based on the CoS.

CPE (Customer Premises Equipment)

Equipment that is located at the customer premises and is owned and managed by the customer.

CR (Cognitive Radio)

A forthcoming device that can seamlessly switch call and transmission modes to whatever makes the most sense, given the location at a given time, whether cellular, Wi-Fi, or VoIP. CR is a smart system in which a radio device and its antenna can adapt their spectrum use in response to their operating environment, including the radio frequency spectrum, user behavior, and network state.

CRC (Cyclic Redundancy Check)

A powerful error-detecting technique. By using a polynomial, a series of two 8-bit block-check characters are generated that represent the entire block of data. The block-check characters are incorporated into the transmission frame and then checked at the receiving end.

CR-LDP (Constraint-Based Routed Label Distribution Protocol)

A protocol in the MPLS architecture that can set up paths to meet traffic-engineering requirements.

crossbar switch

A switch that has a crosspoint for each input/output pair, and only one contact pair needs to be closed to establish an input to output connection.

crosstalk

Interference or an unwanted signal from one transmission circuit detected on another, usually parallel, circuit.

CRTP (Compressed Real-Time Transport Protocol)

RTP compression that affects IP/UDP/RTP headers.

CSD (Circuit-Switched Data)

The original form of data transmission developed for TDMA-based mobile phone systems such as GSM.

CSMA (Carrier Sense Multiple Access)

A LAN access technique in which multiple stations connected to the same channel can sense transmission activity on that channel and defer the initiation of transmission while the channel is active. CSMA is similar to contention access.

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance)

A scheme for controlling network traffic that enables any of multiple nodes to send information over a shared network cable if the cable is free. It avoids collisions by having all nodes signal their intention to transmit before transmitting. If two nodes send intentions to transmit messages at the same time, both nodes wait for random amounts of time before trying again.

CSMA/CD (Carrier Sense Multiple Access/Collision Detection)

A LAN protocol that is a refinement of CSMA in which stations can detect the interference caused by simultaneous transmissions by two or more stations (collisions) and retransmit colliding messages in an orderly manner.

CSU (Channel Service Unit)

A component of CPE used to terminate a digital circuit, such as a leased line or T-1/E-1 facility, at the customer site. A CSU performs certain line-conditioning functions and responds to loopback commands from the local exchange. It also ensures proper 1s density in a transmitted bitstream and performs bipolar violation correction.

CTS (Clear To Send)

A control circuit that indicates to the DTE that data can or cannot be transmitted.

customization

The process of designing or configuring a device, installation, or network to meet the requirements of particular users.

cutover

The physical changing of lines from one system to another, usually at the time of a new system installation.

CVSD (Continuous Variable Slope Delta Modulation)

A speech encoding and digitizing technique that uses 1 bit to describe the change in the slope of the curve between two samples rather than the absolute change between the samples.

CWDM (Coarse Wavelength Division Multiplexing)

A WDM system that was specifically developed for metro area applications. CWDM is based on the same principle as DWDM of accommodating multiple wavelengths on a single fiber, but it uses less expensive lasers, making it cost-effective for metro deployments, cable TV, and enterprise networks. The tradeoff is that greater spacing is required between wavelengths, reducing the total number of wavelengths that can be supported.

CXR (carrier)

A signal of known characteristics (e.g., frequency) that is altered (i.e., modulated) to transmit information.

cycle

One complete repetition of a regularly repeating electronic function. The number of cycles per second, measured in Hertz (Hz), is called the frequency.