CA (Conditonal Access). A satellite system that enables control over access to digital TV services, using encryption. It also offers security in purchase transactions.

CAT (Conditional Access Table) . A DVB/MPEG-2 PSI table that contains information which references an encrypted Conditional Access program.

C band. The bandwidth between 4 GHz and 6 GHz on the electromagnetic spectrum used for satellite transmissions.

C-Message noise. The noise level which can be detected on a channel in the absence of a signal.

C/N (Carrier to Noise Ratio). The ratio in dBs of the carrier signal level to the noise level.

CAI Common Air Interface. The CT2 mobile communication standard (equivalent to GSM) that allows any mobile terminal equipment to be used.

Call answering . A service provided by GSM that answers a call automatically if the subscriber is not available to receive the call. The caller will either be told that the subscriber is not available or, if the subscriber has subscribed to the short messaging service, (SMS), the caller will be given the option to leave a message.

Call card. A prepaid card or credit card issued by carriers for the purpose of making telephone calls.

Call center. A central place where all calls to a network are handled.

Call forwarding. A service provided by GSM that routes calls from the mobile terminal directly to another telephone number.

Call log. A feature that allows you to see the status of the last outgoing and incoming calls on the mobile terminal display and to automatically dial any number on the call log.

Call processing. A sequence of operations performed by the switching system from the time the call is accepted to the end of the call.

Call progress tones. Signals sent by the switching equipment to the subscriber, that indicate the status of the call, for example, engaged tones and dialing tones.

Call setup time. The time taken for a switched call to reach the called party.

Call waiting. A supplementary service that allows an existing call to be put on-hold in order to answer another incoming call, and then alternating between the two calls.

Called party. The subscriber that receives a telephone call (also known as the B-subscriber).

Calling party. The subscriber who makes the telephone call (the A-subscriber).

Capacity. The highest possible transmission speed that can be achieved on a channel without affecting the quality of the signal.

Card. A single WML unit of navigation and user interface. It may contain either information that is to be presented to the user, request input from the user etc.

Carrier. A provider of a wireless cellular telecommunications service.

CATV (Cable TV). TV broadcast that uses cable as a transmission medium.

CBR (Constant Bit Rate). An ATM service category which supports a constant or guaranteed rate to transport services such as video or voice as well as circuit emulation which requires rigorous timing control and performance parameters.

CCITT. CCITT is the International Telegraph and Telephone Consultative Committee, a standards body. CCITT is the former name for the ITU-TS (International Telecommunications Union - Telecommunications Sector).

CDG (CDMA Development Group). An industry association set up in 1994 to promote the world wide development, implementation and use of the IS-95 CDMA standard under the brand name of cdmaOne.

CDMA (Code Division Multiple Access). A method of digital communication that enables a number of cellular conversations to be transmitted on a single radio frequency. CDMA gives each conversation a numerical code that ensures that the correct signal is received by the called party.

CDMA2000 1xEV-DO (1xEvolution - Data Only). Phase 1 evolution of CDMA2000 1xRTT where the 1.25 MHz carrier supports data only. It increases the crucial forward data rate to 2.4 Mbps. Also called IS-856.

CDMA2000 1xEV-DV (1xEvolution - Data/Voice). Phase 2 evolution of CDMA2000 1xRTT, where the 1.25 MHz carrier supports concurrent voice and data. It increases the crucial forward data rate to 3.1 Mbps.

cdmaOne. A brand name, trademarked and reserved for the exclusive use of CDG members that describes a complete cellular wireless systems. It incorporates the IS-95 CDMA air interface and many other standards that make up a complete wireless system.

cdma2000. A system proposed by the CDG for 3G services. It is based upon an evolutionary outgrowth of cdmaOne to allow operators a migration path from second generation cdmaOne system to third generation cdma2000 systems.

cdma2000/1XRTT. An implementation of the multi-carrier cdma2000 standard that uses 1x1.25 MHz carrier.

cdma2000/3XRTT. An implementation of the multi-carrier cdma2000 standard that uses 3x1.25 MHz carriers.

CDR (Call Data Record). A record produced by the mediation device of all toll tickets generated during a call.

Cell. The geographical area covered by a Base Transceiver Station (BTS). Another kind of 'cell' with a different meaning is an ATM cell.

Cell Header. ATM Layer protocol control information

Cell site. The physical structure that contains the control equipment required to connect a mobile station with the switching network. In the GSM network, the cell site is otherwise known as the Base Transeiver Station (BTS).

CEPT (Conference Europeene des Administrations des Postes et Telecommunications). CEPT was prominent in the development of European telecommunications up until 1988 when it handed over its technical standard development activities over to the European Telecommunications Standards Institute (ETSI).

Channel. A 'pipe' that carries a signal frequency.

Channel grade. The indicator of the relative bandwidth of a channel, that is, narrowband, broadband, voice grade.

Channelizing. The subdivision of broadband systems into a number of smaller channels.

CLI (Calling Line Identification). A supplementary service available in digital phone networks that allows the caller's number to be displayed on the mobile terminal display. The call management center achieves this by using equipment that identifies the caller's telephone number and sends it to the subscriber in addition to the call.

Client. The device that initiates a request for connection to a server.

CLP (Cell Loss Priority). This bit in the ATM cell header indicates two levels of priority for ATM cells. CLP=0 cells are higher priority than CLP=1 cells. CLP=1 cells may be discarded during periods of congestion.

CPCS (Common Part Convergence Sub-layer). The part of the convergence sub-layer of an AAL that remains the same regardless of the traffic type.

CPCS-SDU (Common Part Convergence Sub-layer-Service Data Unit). A protocol data unit to be delivered to the receiving AAL layer by the destination CP convergence sub-layer.

CPE (Customer Premises Equipment). End-user equipment that resides on the customer's premises and which may not be owned by the local exchange carrier.

Cluster. A cluster is defined as a group of cells that use all of the available frequencies allocated to the network operator.

Codec (COder/DECoder). It converts analog to digital signals and vice versa. Codec technology is most commonly used in modems.

CRC (Cyclic Redundancy Check). CRC is a technique employed for error control in digital communications systems.

CS (Convergence Sub-layer). The general procedures and functions that convert between ATM and non-ATM formats. This describes the functions of the upper half of the AAL layer and is also used to describe the conversion functions between non-ATM protocols such as frame relay or SMDS, and ATM protocols above the AAL layer.

CSMA (Carrier Sense Multiple Access). A "listen-before-talk" LAN technique used to mediate the access to a transmission resource. All stations are allowed access but must ensure the resource is not in use before transmitting.

CSMA/CD (Carrier Sense Multiple Access with Collision Avoidance). A CSMA technique that tries to avoid simultaneous access to the medium, by deferring access.