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• CAI (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.
  
• CATV (Cable TeleVision) Cable system covering defined areas, such as the U K's franchises to install and operate a cable system granted by the Cable Authority and Department of Trade & Industry, offering TV channel output and, increasingly, local loop digital telephony services The Cable Television Association is the CATV industry's representative organization.
  
• Call processing The system and process that sets up the intended connection in a switching system. A system scans the trunk and station ports for any requests for service. It then checks the stored instructions and look-up tables and sets the connection up accordingly.
  
• Carrier signal The underlying frequency or frequencies that are to carry information. They are modulated through one or more modulation techniques to impose information on the signal.
  
• Category 3 cable Standard for UTP voice grade cabling specified by the EIA/TIA 568 standard for use at speeds up to I0Mbit/s including 10BaseT Ethernet.
  
• Category 4 Cabling standard specified by EIA/TIA 568 for use at speeds up to 20Mbit/s including 16Mbit/s Token Ring.
  
• Category 5 Cabling standard specified by ElA/TIA 568 for use t speeds up to 100Mbit/s including FDDI (TP PMD), 100BaseT and 100BaseVG-AnyLan, and potentially ATM at 155Mbit/s.
  
• CCITT (The International Telegraph and Telephone Consultative Committee) Former name for the ITU-TS (International Telecommunications Union), a Specialized Agency of the United Nations.
  
• CCITT Study Groups The ITU-TS (formerly the CCITT) operates as a series of groups considering specialist areas. There are key study groups applicable to networking and communications such as Study Group VII responsible for data communications networks and the X series Recommendations and Study Group XVIII covering digital networks including ISDN.
  
• CCTA Central Computer & Telecommunications Agency - the Government Center for Information Systems.
  
• Cell Relay Generic term for a protocol based on small fixed packet sizes capable of supporting voice, video and data at very high speeds. Information is handled in fixed length cells of 53 octets.
  
• Centronics interface A parallel interface with 36 pins that will transmit eight data bits simultaneously. The interface originates from the Centronics Company, a printer manufacturer. It has become widely used as a parallel interface standard.
  
• CEPT The European Conference of Postal and Telecommunications Administrations. An association of European Telecommunications service providers. It in turn participates in relevant areas of the work of Cen/Cenelec. Formerly extremely powerful and was originally responsible for the Net standards, but these have subsequently been passed on to Etsi.
  
• Character Interleaving A form of TDM used for asynchronous protocols. This can be used either with extra channels, or by carrying RS232-C control signals.
  
• Cheapernet Thin wire Ethernet.
  
• Circuit switching The transmission technique in which a physical circuit is established between sender and receiver before transmission takes place. When the transmission is complete, the circuit is freed.
  
• CLI (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. Synonymous with ANI (Automatic Number Identification).
  
• Client/server computing The division of an application into two parts; a front end client and a back end server. It allows multiple front ends running on a PC or Unix workstation (client) to access the same SQL based server database at the same time over the LAN. The aim is to off-load as much processing as possible to the intelligent desktop leaving only the shared information and the software for managing it at the central server. An application that is running in such a fashion with client and server linked by a LAN is termed a bifurcated application.
  
• Cluster controller An IBM device that allows multiple 3270 terminals to be linked directly to a host computer, or into a SNA network through the use of a communications controller. A cluster controller is a Control Unit in IBM speak.
  
• CMIP/CMIS (Common Management Information Protocol/Common Management Information Services) ISO OSI connection oriented network management protocol and set of services. Well accepted in the WAN and telecommunications world, they have not yet been widely adopted for LAN management.
  
• CMOT (CMIP/CMIS over TCP) The use of SO CMIP/CMIS network management protocols to manage gateways in a TCP/IP Internet. CMOT is a co-recommended standard with SNMP.
  
• Co-axial cable A cable comprising a central wire surrounded by a second tubular screening of fine wire. Associated with IBM for linking terminals and other devices needing high-speed links, coax is used in Ethernet. It is difficult to add or remove devices from a coaxial LAN as the cable is unwieldy and thick so is being superseded by UTP.
  
• Collision The result of two devices on a shared transmission medium, like Ethernet, transmitting simultaneously. Data is corrupted and both devices must retry their transmissions. A delay mechanism used by both senders drastically reduces the chances of another collision.
  
• Collision detection Devices at each end of a link are designed to detect collisions instantly and attempt to resend. This is the principle on which CSMA/CD is based and the access control method for Ethernet. An alternative is to resend if there is no acknowledgment of receipt from the remote device.
  
• Communications Controller A switching unit central to the implementation of host-based IBM S NA networks. Typically the network is built around a backbone of interlinked communications controllers to which host computers and Control Units (CUs) are attached.
  
• Communications Manager An individual often underpaid and invariably overworked, dedicated to providing cost effective, ultimately flexible networking to users.
  
• Communications Networks The UK's leading monthly magazine for networking professionals and decision makers.
  
• Communications Server A specialized network server that provides access to external networks, communications facilities and hosts that cannot be directly connected to the LAN. Typically it will enable workstation users running appropriate workstation software, such as terminal emulation software, to access asynchronous communications links and typically modems attached to the communications server.
  
• Communications Toolbox An extension of the Apple Macintosh operating system that provides protocol conversion and the drivers needed for communications tasks.
  
• Concentration 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.
  
• Concentrator A central chassis into which various modules, such as bridging, supervisory, 10BaseT and other peripheral cards are plugged.
  
• Connection-oriented service The transport of packets of information from one network node to a destination node following an established network connection.
  
• Connectionless Service The transport of a single datagram or packet of information from one network node to a destination node or multiple nodes without establishing a network connection.
  
• Contention The process whereby multiple users make requests for transmission bandwidth across a transmission link but the pool of bandwidth is less than the aggregate amount of bandwidth the users could request between them. Contention is used to resolve which users gain access to the bandwidth. When this s applied to multiplexers, it is concerned with the multiplexer's ability to allow a number of channels to contend for transmission bandwidth that is less than the sum of all the channel rates.
  
• Control point A program that manages an APPN network node and its resources, enabling communications to other control points in the network.
  
• Converter A repeater that also converts from one media type to another, such as from fiber to copper. Often called a media adapter.
  
• CPE (Customer Premises Equipment) Telecommunications- communications equipment, including PBXs and wiring, located in a user's premises.
  
• CRC (Cyclic Redundancy Check) A method of detecting errors in the serial transmission of data. A CRC for a block of data is calculated before it is sent, and is then sent along with the data. A new CRC is calculated on the received data. If the new CRC does not match the one that has been sent along with the data then an error has occurred.
  
• Cross-Connect An ATM switch usually comprising three functional areas. System control The central control unit, which also provides the management interface of the system; the ATM "fabric block" providing the system switching capacity; termination groups to provide the external interfaces and the functions of the ATM layer of the network node. Each of these functional system areas is configured according to the specified needs of the respective network node. Each functional area usually has its own monitoring and control units for safeguarding the high availability of the complete system.
  
• Crosstalk Unwanted interference from another adjacent communications channel . The signal from the adjacent channel is inserted into the original communications channel.
  
• CSMA/CD (Carrier Sense Multiple Access with Collision Detection) The access method used in Ethernet. All nodes are attached to a single cable and contend equally for access to the transmission medium. if two nodes attempt to send data at the same time, they "sense" each other's signal and immediately stop sending. They will both try to send again after Waiting a random number of microseconds.
  
• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) A method of network access not covered by OSI standards and used in AppleTalk networks.
  
• CSU (Channel Service Unit) (1) In the US, data transmission equipment to repeat the signal from the carrier and ink to CPE. Vendors add value to CSUs by adding performance monitoring and management. (2) In Europe, CSUs are sold for their value features like diagnostics and performance monitoring. The basic repeating function is prd in the NTU (networking terminating unit). CSUs monitor quality on El, E2 or E3 circuits in terms of transmission and line loading.
  
• CT1 First generation analog domestic cordless telephone (non-cellular).
  
• CT2 Two-way digital cordless telephony technology, particularly relevant to cordless PBXs. In its public guise, it becomes a one way telepoint service now no longer available in the UK but prevalent in the Far East.
  
• CT3 Ericsson's proprietary cordless telecommunications system.
  
• CTI (Computer Telephone Integration) A generic name for the technology automatically relating computers and PABXs via applications such as ACD, power dialing, IVR and other customer facing or agent facing services. A so known by older, proprietary names CIT (Computer Integrated Telephony) and CSTA (Computer Supported Telephony Applications).