The 4 GHz to 6 GHz portion of the electromagnetic spectrum used for satellite transmission.

A type of line conditioning that controls attenuation, distortion, and delay distortion so they lie within specific limits.

Client/Server

A distributed computing model in which clients request data and processing from servers. Servers usually have higher capacity than clients. C/S exploits less expensive hardware than host-based computing. But, C/S application design and resource management must be more sophisticated.

Certification Authority

Call Appearance

The point where a marine cable connects to terrestrial facilities.

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.

Carrier Access Code

The sequence an end user dials to obtain access to the switched services of a carrier.

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

Computer-Aided Design/Computer-Aided Manufacture

A computer and its related software and terminals used to design and manufacture things. CAD terminals are often run over LANs and/or WANs.

Controllable ATM Fabric

Common Air Interface

The CT2 international mobile communications standard which allows any compliant equipment to be used on any network of the same type. CAI compliant telepoint handsets from different vendors may therefore be used on a telepoint network. Vendors with CAI compliant systems include Northern Telecom and GPT.

A feature that enables calls to be transferred to a busy extension; the call can be connected to the extension when it is free.

Calls directed to one station can be picked up by another station line within a preset pickup group by dialling a special code.

Time required to establish a switched call between DTE devices.

The user's extension rings when a non-busy trunk is available if outgoing calls cannot be completed due to busy trunk groups, signalling that the call can now be placed.

Caller Identification

Phone company feature which identifies the customer on the line as the call is received.

Content Addressable Memory

A memory device that stores and retrieves data based on a key value, as opposed to an address or name.

The submarine cable between Portugal and Madeira

Customised Applications for Mobile Networks Enhanced Logic

CAMEL is a GSM feature name for including IN (Intelligent Network) functions into a GSM system. CAMEL is used when roaming between networks, allowing the home network to monitor and control calls made by its subscribers. The feature allows numbers dialled to be modified during call set-up, and monitoring of call answer and cleardown. Possible applications include pre-paid roaming services, fraud control, special numbers (e.g. 123 for voicemail works everywhere) and closed user groups (office extension numbers work everywhere). CAMEL has been standardised in three phases, the first of which is starting to be deployed now.

The submarine cable between Canada and Bermuda

The submarine cable between Canada and the U.K.

CAMEL Application Part

Carrierless Amplitude Modulation/Phase Modulation

A line coding protocol

Competitive Access Provider

A company that provides network links between the customer and the interexchange carrier or even directly to the Internet service provider. CAPs operate private networks independent of local exchange carriers.

The highest possible reliable transmission speed that can be carried on a channel, circuit, or piece of equipment. Capacity may be expressed as raw speed or as net throughput.

Process focused on market-based capacity planning and deployment of software-configurable network components.

(1) The act of removing a token from the ring for the purpose of frame transmission.
(2) To 'catch' text that is being sent to your computer from a BBS and put it in a buffer or a file.

(1) Electromagnetic wave or alternating current of a single frequency, suitable for modulation by another, data-bearing signal.
(2)A long-distance company that uses primarily its own transmission facilities, as opposed to resellers that lease or buy most or all transmission facilities from carriers.

A single-channel broadband.

Carrier Access Tariff

The CAT -- which all interexchange carriers, including telephone companies must pay for access to the utility (local) network -- consists of one or more network access components (charges for switching and aggregation, recovery of start-up costs, etc.) and a contribution component to subsidize the rates for basic local telephone service.

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.

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.

Computerized Branch Exchange

Call Control Block

Clear Channel Capability

The bandwidth of a data transmission path available to the end users after control and signalling bits are accounted for. For example, in a 64Kbps channel, all 64Kbps is available for data transmission.

Consultative Committee on International Radio

An international committee that defined the 625-line television system used in Western Europe. The US system uses 525 lines, while ISDN (integrated services digital network) TV uses 1,125 lines.

A digital technology used by AT&T to enhance their Integrated Services Digital Network (ISDN). CCIS uses a separate data line to route interoffice signals to provide faster call set-up and efficient use of trunks.

Consultative Committee on International Telegraphy and Telephony

International organization responsible for the development of communications standards. Now called the ITU-T.

Used to negotiate compression methods over PPP links.

Common Control Redundancy

A feature that allows configuration of a redundant common control unit; in the event of the main control failure, the redundant unit automatically switches on.

Common Channel Signalling

Signalling system used in telephone networks that separates signalling information from user data. A specified channel is exclusively designated to carry signalling information for all other channels in the system.  (See also CAS)

Common Control Switching Arrangement

The use of carrier switches under a carrier's control as part of a customer's private network. The carrier's software controls the customer's calls over private lines rented by the customer. Switch control and switching functions is performed in common for all users.

A private branch exchange (PBX) feature that allows a user to gain entry to a common control switching arrangement (CCSA).

Central Computer & Telecommunications Agency

The Government centre for information systems.

Carrier Detect

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

Call Directing Code

A character string used to address a terminal for automatic routing of messages in teletype systems.

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.

Channel Definition Format

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

Code Division Multiple Access

A digital cellular phone service that offers up to 20 times more call-handling capacity than conventional cellular systems by assigning a special electronic code to each signal, allowing more calls to occupy the same space and be spread over an entire frequency band. Developed by Qualcomm Inc., which promotes CDMA as an alternative to Time Division Multiple Access technology (TDMA).

A radio transmission technology and backbone technology for the evolution of cdmaOne/IS-95 to 3G.

Cellular Digital Packet Data

A system that transmits packets of data over cellular networks without interfering with voice transmission.

Call Data Record

Information sent from a circuit switch to track the time and duration of a call or the amount of packets or data; event record which may include transaction ID, type of transaction, destination/origination, start time, duration or end time (packets or seconds).

Consumer DSL

Trademarked version of DSL, slower than ADSL (1 Mbps downstream, probably less upstream) but has the advantage that a "splitter" does not need to be installed at the user's end.

Cell Delay Variation

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

Cell Delay Variation Tolerance

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

Conditioning Equipment

Equipment that provides modifications or adjustments necessary to match transmission levels and impedances. CE also equalizes transmission and delay to bring circuit losses, levels, and distortion within established standards.

A fixed-length transmission unit which forms the basis of ATM. Each cell is 53 bytes in length, divided into a 48-byte payload and a 5-byte header.

A packet transmission system that uses fixed-length cells which can be processed and switched at very high speeds, making it possible to use a single transmission scheme for voice, data, and video traffic on local- and wide-area networks.

A feature that enables a caller to move from one location to another without losing the connection. The cellular system is designed to switch calls to a new call without a noticeable drop in the connection. While not noticeable in voice communications, the 300 milliseconds required for cell switching can cause problems in data transmission. Cell switching is sometimes referred to as handing off.

A networking technology which breaks up geographical areas into clusters of small honeycomb-shaped cells. The network consists of one low-powered output cell site per cell, cellular handsets, and the MSC, which all exchange information to connect cellular subscribers.

Code Excited Linear Prediction Compression

Compression algorithm used in low bit-rate voice encoding.

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.

European Laboratory for Particle Physics

Birthplace of the World Wide Web.

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.

Carrier Facility Assignment

An identifier for the circuit assignments a local exchange carrier (LEC) uses at the point where it interconnects with other facilities. (2) An identifier for the telephone company network point where an interexchange carrier (IEC) connects.

Cisco Frame Relay Access Device

Common Gateway Interface

Programs use the CGI specifications to communicate with Web servers and produce interactive, 'intelligent' Web pages, Such programs are often referred to as CGIs, or CGI scripts.

A portion of a line's bandwidth. A line contains a fixed number of channels. Each line can contain switched channels only, nailed-up channels only, or a combination of switched and nailed-up channels.

Channel aggregators, also known as inverse multiplexers, are devices that allow very large amounts of data to be sent down the narrow band channels of ISDN. The aggregator effectively pulls together ISDN channels at one end to form a higher bandwidth and then re-synchronizes the information at the other end. Re-synchronization is necessary because during transmission the ISDN channels may send the information along different routes, meaning it arrives at its destination at fractionally different times.

A measure of the maximum amount of data that a channel can manage.

A device that increases the distance a mainframe can communicate with other mainframes and input/output devices, such as remote terminals, tape drives, and high-speed printers at local channel speeds over T1/T3 lines.

The relative bandwidth of a channel: narrowband, voice grade, or wideband.

The equipment such as multiplexers and channelizers, required to provide a connection point for one channel. A recurring charge rate element is levied on each channel termination for dedicated circuits.

To subdivide or break out a broadband transmission system into multiple communications channels.

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.

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.

The isolation and testing of a particular data path out of many such paths included in a conglomerate data signal.

Challenge Handshake Authentication Protocol

A security protocol allows access between data communications systems prior to and during data transmission. CHAP uses challenges to verify that a user has access to a system.

A form of TDM used for asynchronous protocols. This can be used either with extra channels, or by carrying RS232-C control signals.

The process of adding a redundant overhead bit to a character to provide error detection capability.

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.

Thin wire Ethernet.

China' s public data network.

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

Customer Information Control System

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

Craft Interface Device

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

Channel ID

Designates the Frame Relay sub-channel ID for Voice over Frame Relay.

Classless Inter-Domain Routing

An address aggregation process that simplifies routing.

Committed Information Rate

The minimum bandwidth guaranteed to be available if required on a virtual circuit. This value is also known as guaranteed bandwidth.

(1) A path for the transmission of electromagnetic signals to include all conditioning and signalling equipment.
(2) A switched or dedicated communications path with a specified transmission speed or bandwidth capacity.

The data-carrying ability of a circuit measured in speed or type of signal, such as broadband, voice grade, sub-voice, and telegraph.

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."

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.

Computer Integrated Telephony

The linking of telephone and IT systems to provide a seamless service to customers, whatever their means of contact.

Commercial Internet Exchange

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

Custom Local Area Signalling Services

A set of intelligent services for residential and small-business subscribers, including call forwarding, call waiting and three-party conferencing, provided by Bell companies and increasingly in other countries outside the USA.

A rank assigned to a switching office, according to its functions, relationships to other switching offices, and transmission requirements, in the telephone network.

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.

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

Competitive Local Exchange Carrier

A company that provides local dial-tone services as well as long-distance, data, and Internet services, usually to businesses.

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.

Command Language Interpreter

Basic Cisco IOS configuration and management interface.

Calling Line Identification

A service available on digital phone networks that tells the person being called which number is calling them. The central office equipment identifies the phone number of the caller, enabling information about the caller to be sent along with the call itself.

Called Line Identification

A facility provided by a switched network in which the network confirms for the calling terminal, the telephone number of the line to which the call has been connected.

Any computer connected to a network that requests services (files, print capability) from another member of the network.

The division of an application into two parts, with one part running on a server and the other running on a PC or workstation. It can be described as an architecture for LAN application programs. The rationale behind client/server computing is to exploit the local, desk top processing power leaving the server to govern the centrally held information. This should not be confused with PCs holding their own files on a LAN, as here the client or PC is carrying out its own application tasks. Nevertheless, such systems are helping the market move in the direction of true client/server computing, the advantages of which include less network traffic and more flexibility.

This occurs when the first words during a telephone conversation are broken off or "clipped," because the line is being shared by many conversations. This usually occurs on overseas channels.

Connectionless Network Protocol

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

Connectionless Network Service

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

The end of a line, such as a wide area telecommunications service (WATS) 800 or a foreign exchange line, from which all calls are directed to or from a single point. Private lines normally have two closed ends.

Cell Loss Priority

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.

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.

Configuration Management

In fibre-distributed data interface (FDDI), that portion of connection management that provides for the configuration of physical layer protocol (PHY) and media access control (MAC) entities within a node.

Construction and Maintenance Agreement

An agreement for the ownership, construction and maintenance of expensive facilities, such as transoceanic cables and related equipment. CMAs are usually between multiple carriers, but may be between a carrier and a government.

Noise level measured on a channel in the absence of signal (voiceband).

Common Management Information Protocol

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

Common Management Information Services

Network management protocol.

Connection-Mode Network Service

Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring).

Complementary Metal Oxide Semiconductor

Chips made with this low-power semiconductor technology are commonly used in personal computers to hold basic start-up information--such as the time and date--for use by the system's BIOS.

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.

Carrier Non-Compatible Applications

Applications which rely on metallic facilities (i.e., copper) with direct current continuity to provide service. Certain older applications, such as some provided by alarm companies, energy monitoring companies and other users of telemetry, could not generally be multiplexed, carried over digital facilities (i.e., fibre optics) or transported over radio facilities.

Customer Network Management System

A network management system to provide customers with network monitoring and service request capabilities. This system is located at the customer's facility.

Noise level measured with a 1004-Hz signal present, but removed at the measurement end (voiceband).

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.

Central Office Frame Relay Access Device

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 signalling, and 75-ohm cable, which is used for analogue signalling and high-speed digital signalling.

Common Business-Oriented Language

A high-level programming language adopted in 1960 for use on minicomputers and mainframes in business environments.

Coder-Decoder

Integrated circuit device that typically uses pulse code modulation to transform analogue signals into a digital bit stream and digital signals back into analogue signals. (2) In Voice over IP, Voice over Frame Relay, and Voice over ATM, a DSP software algorithm used to compress/decompress speech or audio signals.

Electrical techniques used to convey binary signals.

Central Office-based Local Area Network

A collection of computers on one or several business premises interconnected through public telephone lines and acting as a single, physically-connected network.

A process that enables a group of distant participants to jointly view, discuss, and edit documents while using communications and computing resources. This can be considered an extension of conventional audio/video conferencing which employs media communications and information access. Collaborative working represents a case of complex and dynamic communication that encompasses a number of participants, connections, information types, systems, and functions.

Non-distributed 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.

A collection point for data from a number of end offices. Data is combined into a single bit stream for transmission back to the hub office. A collection hub does not have test capability, MJUs, or analogue extension equipment.

The placement of in-service, customer telecommunications equipment at a carrier's central office (CO), point of presence (POP), or other network location.

A submarine cable between Spain and Venezuela.

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

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.

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."

The submarine cable that links Canada, Fiji, New Zealand and Australia.

Contraction derived from the opposite processes of compression and expansion. Part of the PCM process whereby analogue 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.

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.

The connection of transmission channels in a chain.

A technique used to get the most out of a composite multiplexer link. Usually a statistical multiplexer, or concentrator, is used to focus channel inputs on to the composite ink by removing the portions of the transmission carrying no data.

A network device used in fibre-distributed data interface (FDDI) and token ring networks to provide connections between multiple stations, allowing them to communicate with other stations on the network. It provides a logical star topology while stations are physically connected as a ring. The concentrator is the centre of the star topology and can actively bypass a port connected to it. A fibre-distributed data interface (FDDI) concentrator has at least two physical layer entities and may or may not have one or more media access control (MAC) entities. In Ethernet networks, a similar function is performed by a repeater.

Element management service tool with a GUI.

Traffic in excess of network capacity.

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.

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-Oriented Network Protocol

OSI protocol providing connection-oriented operation to upper-layer protocols.

Connection-Oriented Network Service

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.

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

A set of specifications for management object modelling and for interactions between objects.

Primary routers in the Internet.

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

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

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."

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.

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.

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.

Calling Party Category

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.

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

Characters Per Second

The number of bytes or characters sent over the phone lines in 1 second.

Control Packet Switching System

A signalling protocol that supports exchange of information on private-line services and virtual circuits, operating in time division multiplexing, X.25, X.75, frame relay and ATM systems.

Central Processing Unit

Custom Queuing

Card Query Language

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.

Cycle 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.

Conduit, Raceway, Equipment Ducts, and FACilitieS.

The infrastructure used in cabling.

Customer Relationship Management

The use of software systems to target and serve customers by using data intelligently. Products can be tailored to individual needs.

Customer Reservation System

Cathode Ray Tube

The coding of communications to ensure privacy.

Convergence Sublayer

Part of AAL

Capability Set 1

A set of service-independent building blocks for the creation of IN services developed by the European Telecommunications Standards Institute and the CCITT.

Call State Control Function

Circuit Switched Digital Network

Called Subscriber Identification

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

Customer Service Manage

Also known as Customer Account / Operations Manager, employee responsible for developing customer care standards, plans, and processes, then managing the customer care department and CAS employees.

Carrier Sense Multiple Access/Collision Avoidance

Is the principle medium access method employed by IEEE 802.11 WLANs. It is a "listen before talk": method of minimizing (but not eliminating) collisions caused by simultaneous transmission by multiple radios. IEEE 802.11 states collision avoidance method rather than collision detection must be used, because the standard employs half duplex radios—radios capable of transmission or reception—but not both simultaneously. Unlike conventional wired Ethernet nodes, a WLAN station cannot detect a collision while transmitting. If a collision occurs, the transmitting station will not receive an ACKnowledge packet from the intended receive station. For this reason, ACK packets have a higher priority than all other network traffic. After completion of a data transmission, the receive station will begin transmission of the ACK packet before any other node can begin transmitting a new data packet. All other stations must wait a longer pseudo randomized period of time before transmitting. If an ACK packet is not received, the transmitting station will wait for a subsequent opportunity to retry transmission.

Carrier Sense Multiple Access/Collision Detection

The LAN access method used in Ethernet. When a device wants to gain access to the network, it checks to see if the network is free. If it is not, it waits a random amount of time before retrying. If the network is free and two devices access the line at exactly the same time, their signals collide. When the collision is detected, they both back off and each wait a random amount of time before retrying.

Circuit Switched Public Data Network

Channel Service Unit

A device used to connect a digital phone line coming in from the phone company to network access equipment located on the customer premises. A CSU may also be built into the network interface of the network access equipment.

Channel Service Unit / Data Service Unit

Manages digital transmission, monitors signals for problems, responds to Central Office commands. It performs many of the functions that modems do, but it does not have to convert digital signals to/from analogue, since the end device and the underlying transmission facility are both digital.

Capability Set 2

A specification for the digital second generation of cordless telephones (a British digital cordless communications system).

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.

Cellular Telecommunications Industry Association

An organization that promotes cellular technology, addresses common cellular concerns, provides a forum for exchange of information, as well as a lobbying voice in the legislature.

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.

Customer Premise Transceiver

Reunion CPE radio and antenna

Clear-to-Send

The signal transmitted to a sending modem to start the data transmission process.

Control Unit

A device that concentrates data from several terminals onto a single communications line.

Control Unit

The central processor of a telephone switching device.

Closed User Group

A subgroup of network users that is treated as an entity. Member can communicate only with other members of that subgroup.

Continuously Variable Slope Delta Modulation

A type of delta modulation in which the step size of an approximated signal are progressively increased or decreased as required to make the approximated signal closely match the input analogue wave.

Continuous Wave