Index - A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z
C BAND - A portion of the electromagnetic spectrum used heavily microwave and satellite transmission; frequencies in the region of 4 Gigahertz to 6 Gigahertz.
C CONDITIONING - A type of line conditioning that puts specified limits on amplitude and delay distortion to keep them within tolerable limits for certain data transmissions. CABLE -An assembly of one or more wire conductors or optical fibers within an envelope (commonly called a sheath ) so as to permit use of the conductors singly or in groups.
CARRIER - 1.) a signal of known characteristics that is modified ( modulated )so it carries information. The receiver, knowing the expected characteristics of the carrier, can extract the information from it. However, noise or unintended changes to the carrier will, of course be also interpreted as part of the information. 2.) See "Common Carrier."
CARRIER ACCESS CODE (CAC) - The sequence an end user dials to select access to the switched services of a carrier. Carrier Access Codes for Feature Group D are composed of five digits, in the form 10XXX, where XXX is the Carrier Identification Code.
CARRIER ACCESS LINE CHARGE (CALC) - A per minute charge paid by long distance companies to local phone companies for the use of local public switched networks at either or both ends of a long distance call. This charge goes to pay part of the cost of local telephone poles, wires, etc.
CARRIER IDENTIFICATION CODE (CIC) - The three-digit number that uniquely identifies a carrier. The Carrier Identification Code is indicated by XXX in the Carrier Access Code,dialed by customers in the form 10XXX. The same code applies to an individual carrier throughout the area served by the North American Numbering Plan.
CARRIER SENSE MULTIPLE ACCESS (CSMA) - A LAN access method in which stations listen to see if the transmission path is clear before starting to transmit.
CARRIER SENSE MULTIPLE ACCESS/COLLISION DETECTION (CSMA/CD) - A refinement of CSMA in which stations can identify not only an idle channel, but if a collision has just occurred, in which case they wait additional time to give the preceding stations access priority to clear their traffic.
CARRIER SYSTEM - A transmission system capable of providing multiple communications channels over a single physical path. CABLE TELEVISION ; COMMUNITY ANTENNA TELEVISION (CATV) - Telecommunications based on guided radio frequency ( RF ) transmissions using 75 - Ohm coaxial cable as the physical medium. Cable TV offers multiple frequency - divided channels, permitting mixed transmissions to be carried simultaneously. Broadband LANs are a variant of Cable TV technology.
CATHODE RAY TUBE (CRT) - A common form of visual display for data terminals, similar to a television picture tube.
CCIR - Comite Consultatif Internationale des Radio, a major constituent of the International Telecommunications Union ( See "ITU", issuing both Radio Regulations and Recommendations for all uses of radio transmission.
CCITT - Comite Consultatif Internationale des Telephones et Telegraphes, a major constituent of the International Telecommunications Union ( ITU ) that sets standards for the operation of telecommunications services across international boundaries. Many CCITT standards are adopted for use domestically.
CCITT SIGNALING SYSTEM NUMBER 1 (SS1) - A tone supervision system using a 500 Hertz tone modulated at a 20 Hertz rate to signal call requests between switchboards. International equivalent of Bell's 1000/20 manual ringdown signaling.
CCITT SIGNALING SYSTEM NUMBER 2 (SS2) - A two-tone (600/750 Hertz) system for dial-pulsing selection information; never used internationally, closely akin to early Bell mobile radiotelephone dialing systems.
CCITT SIGNALING SYSTEM NUMBER 3 (SS3) - A single- frequency (2280 Hertz) tone system used on one-way circuits only; not intended for transit connections involving a third nation; a prime method through the late 1970's.
CCITT SIGNALING SYSTEM NUMBER 4 (SS4) - A two-tone (2040 and 2400 Hertz) system for international transit and terminal traffic; the first truly global "direct dialing" signaling system.
CCITT SIGNALING SYSTEM NUMBER 5 (SS5) - A two-tone (2400 and 2600 Hertz) system combined with multifrequency inter- register signaling for both terminal and transit traffic; closest international equivalent to North American Bell "DDD trunks using SF supervision."
CCITT SIGNALING SYSTEM NUMBER 6 (SS6) - A common digital data path between two switching machines to negotiate and oversee connection control on transmission facility trunks between the machines; international equivalent of Bell CCIS; typically a 2400bps data circuit.
CCITT SIGNALING SYSTEM NUMBER 7 (SS7) - Sends packetized machine-language messages about each call connection between and among machines of a network to achieve connection control; international equivalent of Bell DNHR; permits many ISDN services such as CNID or Random RCF; typically a 64 kilobit data circuit.
CCITT SIGNALING SYSTEM R1 - International equivalent of Bell 2600 Hertz "SF signaling" used in North American "DDD trunks." Largely used only in Third World nations.
CCITT SIGNALING SYSTEM R2 - International equivalent of Bell "out of band" analog carrier system signaling; uses a tone of 3825 Hertz placed between voice channels of a carrier system; used primarily in Europe.
CELLULAR MOBILE RADIO - A high capacity land mobile radio system in which its radio channels are divided into clustered groups covering limited areas, with the radio units automatically switching channels as the user moves from cell to cell.
CENTRAL OFFICE (CO) - With local telephone companies, the nearby building containing the local telco switch which provides local telephone service. Also the physical point where calls enter the long distance network. Sometimes referred to as Class 5 office, end office, or Local Dial Office.
CENTREX/CO - PBX Service provided by a switch located at the telephone company central office.
CENTREX/CU - A variation on Centrex CO provided by a telephone company maintained "Central Office" type switch located at the customer's premises.
CHANNEL - A communications transmission path via any sort of transmission medium - wire, radio, optical fiber or otherwise.
CHANNEL BANK - Hardware typically used in a common carrier office that performs the end point multiplexing and demultiplexing of individual channels to and from a telephone-type carrier system; including provision for supervisory signaling used by telephone switching systems.
CHANNEL SERVICE UNIT (CSU) - A part of CPE terminating a physical digital circuit such as a DDS or T-1 facility; forms up the digital stream into bipolar signals suitable for line transmission, performs loopback functions, and more recent versions provide overall error measurement in operation. The central office equivalent is an Office Channel Unit, or OCU.
CHANNELIZATION - Division of a larger capacity channel into a number of smaller channels for use by multiple functions.
CHARACTER - a unit of typographic information, usually variable as part of a language. Because data is handled and transferred as a series of characters,the term also can mean one bit pattern in a specific data code; frequently called a "word" in the computer programming sense of the term. In digital ( T carrier ) communications lines, " octects " are for all practical purposes synonomous with data communications characters, in their nature as 8-bit "words" conveying the instantaneous amplitude level of their transported signal.
CHARACTER ORIENTED - Descriptive of a communications protocol or transmission procedure that has control information transmitted in the form of special bytes called control characters. Implies by its nature limitation to a particular character code. Compare to " bit oriented ".
CIRCUIT - A path including any needed supervisory and signaling or conditioning equipment for the transmission of electromagnetic signals. - Synonym: Facility, Transmission Facility.
CIRCUIT CONDITIONING - Modification of (most typically) analog data circuits to bring transmission parameters of the channel into narrower limits than provided by randomly-selected voice channels; conditioning is also utilized to a lesser extent in certain other services.
CIRCUIT SWITCHING - A switching system that completes a dedicated transmission path from sender to receiver at the time of transmission, then releases that path for another user when the transmission is completed. Closely akin to "session" in data systems. Compare to Message Switching and Packet Switching .
CLADDING - In fiber optic cable, a low refractive index material surrounding the core of each optical fiber, providing guidance to the lightwaves within the fiber.
CLASS OF SERVICE/CLASS MARK (COS) - An identifier to group customers or users for the purpose of rate distinction or setting of service functions and features.
CLOCKING - Repetitive, regularly timed signals used to control synchronous transmissions.
CLUSTER CONTROLLER - A device that handles remote communications control (and sometimes processing) for multiple data terminals or workstations.
COAXIAL CABLE - A cable in which one conductor surrounds the other. The electromagnetic wave travels between the grounded outer shield and the central conductor. Coaxials can carry much wider bandwidth and higher frequencies than twisted wire pair, while suffering less interference problems due to the grounded outer conductor. Where the maximum frequency capable on twisted pair wiring is about 16 megahertz and then only for short distances, coaxial cable readily carries several hundred megahertz for a thousand feet.
CODEC - Contraction of Coder-Decoder. Used to convert analog signals to digital pulses for transmission and back again to the original analog form for reception. Originally located in digital channel banks, codecs are now located within digital telephone sets.
COLLISION - Simultaneous transmissions on a LAN that interfere with each other in a contention-based access scheme. Occurs when two or more terminal devices attempt to transmit at nearly the same instant; token-passing schemes avoid this, while well-planned contention schemes keep it to a tolerable level.
COMMON CARRIER - A business enterprise offering telecommunications services and facilities to the general public.
COMMON CHANNEL INTEROFFICE SIGNALING (CCIS) - A digital technology used by AT&T; uses a separate data line to route interoffice signals providing faster call set-up and more efficient use of trunks than can trunk groups with discrete signaling; closely equivalent to CCITT Signaling System Number 6 (which see elsewhere).
COMMON CONTROL SWITCHING ARRANGEMENT (CCSA) - The use of common-carrier owned switching machines as part of a customer's private network. The carrier's software controls and switches the customer's calls over private lines the customer has rented; primary function is for intercity use as compared to the primarily local function of centrex (which see elsewhere).
COMMON CONTROL SYSTEM - An automatic switching system that makes use of common equipment to establish a connection. Once connection is made, the common control equipment is available to establish another connection.
COMPANDOR - Contraction of "Compressor/Expandor." 1.) In analog operations, used to transmit signals higher above noise with a restricted dynamic range, then restore that range by expansion at the receiver; 2.) In digital systems, used to restrict the dynamic range of speech signals prior to digital transmission encoding, then expand them at the receiving terminal.
COMPATIBILITY - A property in data processing and telecommunications systems permitting exchange of information directly and in usable form; implies identical or interchangeable signals and methodologies. Achieving compatibility is a major function of standards organizations.
COMPRESSION - 1.) In analog communications, restricting the range of volume levels of signals in order to transmit them at a higher average power above noise on the channel; 2.) In data communications, compacting the number of bits used to represent the information, losing the character structure while reducing the circuit time or capacity needed to transfer the data; decompression is then needed at the receiving end to again render the data useful.
CONCATENATION - Linking of transmission media by looping through devices; used in various ways by many data terminals, this term most closely associated with Burroughs data terminals. Other names: Daisy Chaining ( NCR ), Multiple Wiring ( telephony ), Paralleling , Looping .
CONCENTRATOR - Any communications device that allows a shared transmission medium to accommodate more terminals than channels available on the medium. Other names: Contention switches , Channel Contenders .
CONDITIONED CIRCUIT - A circuit with added equipment to obtain desired characteristics for transmission; most commonly associated with analog data transmission circuits, correcting amplitude and envelope delay characteristics that give rise to timing jitter in demodulated data. The addition of such equipment is called " conditioning ".
CONDITIONING EQUIPMENT - Equipment added to a circuit for the express purposes of matching transmission levels and impedances or equalizing transmission and delay to bring circuit losses, levels, and distortion within specified limits of CCITT standards, or in U.S. practice, common carrier tariffs.
CONFIGURATION - The combination of long-distance services and/or equipment that make up a communications system.
CONTENTION - A method of line or resource control in which multiple terminals request use of a line or resource at random from the remote end to transmit. Compare with "polling ".
CONTINUITY CHECK - 1.) In wiring, verifying that tandem wires have in fact a continuous path, an inadequate test of transmission viability for sophisticated applications; 2.) In common-channel signaling arrangements, a short test performed to verify that a path has been established just before cutting it through to the user.
CONTROL CHARACTER - A character inserted into a data stream to notify the receiver of a special function to perform or to identify the purpose of the data or message associated with it. While permitting simpler terminal equipments, control characters add a throughput burden to transmission links and limit transparency sufficiently that modern protocols seek to eliminate their use. The " framing bits " of ESF digital carrier are synonomous with control characters in data transmission.
CONTROL MODE - The state data terminals must be in to permit line control actions to occur. A telephone equivalent is muting of the transmitter when a keypad button is depressed to prevent extraneous noises at the instant of dialing tone transmission.
CONTROL SIGNALS - Signals passed between parts of a communications system to oversee operation and configuration of the system. In telephony, supervision signals are a form of control signal.
CONTROL UNIT (CU) - The central processor of a telephone switching device; may be mechanical or electronic.
CONVERSATIONAL MODE (CHAT MODE) - Interactive data communications carried on between data terminals in a fashion emulating speech conversation.
COS - 1.) In the telephone switching sense, "Class of Service" (which see elsewhere); 2.) In the data processing sense, "Corporation for Open Systems."
COST COMPONENT - The price of each element of telecommunications service and/or equipment that comprises a configuration (which see elsewhere).
CR (CARRIAGE RETURN) - A control character causing the print or display position to move to the first position on the line, drawn from the typewriter and teleprinter function with similar action.
CROSS CONNECTION (X-CONNECT) - 1.) In the physical wire sense, wire connections running between two points on a distribution frame, or between binding posts in a terminal wiring box; 2.) In digital communications systems, a bit stream addressed between two ports of a switching or routing unit. See also "digital cross- connect."
CROSS TALK - Unwanted energy (speech, tone or digital pulses) transferred from one transmission path to another. Comprises part of the "noise" observed on analog communications circuits.
CURRENT LOOP - A digital transmission method that recognizes current flows as compared to voltage changes; long used in telegraphy, some use is found in vendor proprietary terminal interfaces, most notably those of Digital Equipment Corporation.
CUSTOMER ACCESS LINE CHARGE (CALC) - The FCC-authorized monthly surcharge added to all local lines to recover a portion of the cost of telephone poles, wires, etc., from end users. Before deregulation, a large part of these costs were financed by long distance users in the form of higher charges.
CUSTOMER INFORMATION CONTROL SYSTEM (CICS) - An IBM computer system function to oversee and control the flow of information by means of software interfaces between application programs and the computer's operating system.
CUSTOMER OWNED AND MAINTAINED (COAM) - Customer provided communications apparatus and associated wiring.
CUSTOMER PREMISE EQUIPMENT (CPE) - Telephone equipment, usually including wiring located within the customer's part of a building.
CUT - To transfer a service from one facility to another.
CUTOVER - The function of transferring a service from one facility to another; most often in the sense of changing switching machines, accomplished during a night or weekend.
CUT THROUGH - Connecting of a path for signaling and/or communications between two points through an intermediary or "transit" point; known in telegraphic communications as "DF."
CYCLIC REDUNDANCY CHECK (CRC) - A powerful error checking method for data and digital communications. The transmitting terminal computes a numeric value representative of the number of marking bits in the associated block of data and sends that value to the receiver, where the number is recomputed to compare against the block as received. Depending on the number of bits in the CRC numeric value the error trapping efficiency ranges from about 97 % at CRC-6 to 99.997% at CRC-32. Values of CRC-8 and CRC-16 are adequate for most data message block sizes, while CRC-32 is needed mainly for very long blocks of tens of thousands of characters.