C band – A portion of the electromagnetic spectrum used heavily for satellite and microwave transmission; frequencies of approximately 4 to 6 GHz.
Cache memory – A high-speed, buffer-type memory filled at medium speed from the main memory. [Programs and instructions found in the cache memory can be operated at higher speeds without the necessity of loading another segment.]
Call-by-call selection – The ability to switch calls to individual trunks, rather than trunk groups, and to transmit necessary information to the specific trunk-type necessary to complete the call. [ISDN feature with Sprint.]
Call detail record (CDR) – Computer record containing data unique to a specific call. [This information is processed as a unit and contains such details as originating switch, terminating switch, call length and time of day.] (2) Processing of call-specific information — start time, elapsed time, number dialed, date, and other pertinent customer data — to provide call detail reports and invoices.
Call forward/with reason display – Enables the called number, during an internodal call, to forward the incoming call to an alternate destination and provide a message explaining why the call is being forwarded.
Calling name delivery – Provides the ability during call setup to deliver the name of the calling party from the originating to the terminating switch or the name of the connected party from the terminating to originating switch. [ISDN feature with Sprint]
Camp (or camp-on) – A PBX feature where a telephone line is busy and the incoming call is placed in a waiting mode until the line is available, at which time the call is automatically put through.
Canned program – A software program written to meet the expected customer needs of a certain application. Opposite of custom programs.
Capability - Data processing equipment characteristic by which one machine may accept and process data without conversion or code modification.
Carrier – (1) A company authorized by appropriate regulatory agencies to provide communications services. (2) A continuous frequency capable of being modulated or impressed with a second information carrying signal.
Carrier modulation – A signal at some fixed amplitude and frequency which is combined with an information bearing signal in the modulation process to produce and output a signal suitable for transmission.
Carrier system – A method for providing several communications channels over a single path. Accomplished by modulating the data, voice or video transmissions onto a higher frequency carrier wave, then recovering it at the receiving end through a process of demodulation (See Frequency Division Multiplexing.)
Categories of service – Basic and enhanced, as defined by the Federal Communications Commission (FCC). [Basic service refers to transmission capacity for the movement of information; for example residential telephone service. Enhanced service combines basic service with computer processing; for example Electronic Yellow Pages.]
Cathode ray tube (CRT) – A vacuum tube display in which a beam of electrons can be controlled to form alphanumeric characters or symbols on a luminescent screen, for example, by use of a dot matrix.
Cellular mobile radio – A radio-based system providing exchange telephone service to a station located in an auto or other mobile vehicle or device (for example briefcase). [Radio circuits transmitted to/from a base radio station cover a specific geographical area. As the vehicle or device moves from one area to another, different base radio stations handle the call.]
Central office (CO) – (1) Location of telephone switching equipment where customers’ lines are terminated and interconnected. (2) Switching center that provides local access to the public network. Sometimes referred to as: End Office, Local Dial Office, Wire Center or Switching Center.
CENTREX - A type of private branch exchange service where incoming calls may be dialed direct to extensions without operator assistance. Outgoing and intercom calls may be dialed by extension users.
CENTREX, CO – Arrangement in which the Local Exchange Company’s service-providing switch is located in its central office.
CENTREX, CU – Arrangement in which the PBX features are provided by a switching system located on the customer’s premises, but work under the control of, or in conjunction with, equipment located in a LEC central office.
Channel – (1) The smallest subdivision of a transmission system by means of which a single type of communication service is provided, for example, a voice channel or a data channel. (2) A communications path via a carrier or microwave radio. (3) In data communications, a path for electrical transmission between two or more points. (4) Within a computer, the electronic paths along which data flows between the input-output units of a computer and the customer premises equipment (CPU). Synonym: circuit, facility, line, link or path.
Channel bank – (1) A part of the carrier system that performs the first step of modulation. (2) A multiplexer that modulates a group of channels into a higher frequency band and, conversely, demultiplexes the higher frequency band into individual channels. It can break a signal into the equivalent of 24 analog voice grade and/or 56 Kbps digital channels.
Channel capacity – The maximum bit rate that can be handled by a channel.
Channel mileage charge – Monthly leased rate for circuits between telephone company (telco) central offices.
Channel service unit (CSU) – Premises equipment that complies with Bell Technical Publication 62411 in providing loopback, keep-alive signals, alarm and status conditions.
Channel termination charge – Fee associated with a T1 for the circuits feeding into a telco central office.
Channel, four-wire – A two-way circuit, each with backup, where the signals simultaneously follow separate and distinct paths in opposite directions in the transmission medium.
Character - (1) Any alphabetical letter, digit or special symbol. (2) In data transmission, the representation of a letter number or symbol by a specific code made up of binary digits.
Character-oriented – A communications protocol or transmission procedure that carries control information encoded in fields of one or more bytes.
Chips – Miniaturized microprocessors built on a single piece of silicon. [Typically, less than 1/2-inch square, they contain all the essential elements of a central processor, including the control logic, instruction decoding and arithmetic processing circuitry. Microprocessor chips are combined with memory and I/O integrated circuit chips to form a microcomputer, which usually fill no more than a single printed circuit board.]
Circuit - A path for the transmission of electromagnetic signals; includes all conditioning and signaling equipment. Synonym: facility.
Circuit grade – (1) The information-carrying capability of a circuit, delineated in speed or signal type. (2) For data use, capability within certain speed ranges.
Circuit switching – (1) A method of communications, where an electrical connection between calling and called stations is established on demand for exclusive use of the circuit until the connection is released. (2) A switching system that completes a dedicated transmission path from sender to receiver at the time of transmission. See also: packet switching, store and forward, message switching.
Class of service (COS) – (1) Telephone service distinctions which include: rate differences between individual and party lines, flat rate and message rate, and restricted and extended area service. (2) A subgrouping of telephone customers or users for the sake of rate distinction or limitation of service.
Clock – A repetitive signaling device used to control a synchronous computer.
Cluster controller – A device that handles the remote communications processing for multiple terminals or workstations.
Coaxial cable - Cable consisting of an outer conductor surrounding an inner conductor, separated from each other by insulating material. It can carry a much higher bandwidth than a wire pair.
CODEC – Equipment containing a coder plus a decoder. Used to convert analog signals to digital form for transmission over a digital medium and back again to the original analog form.
Cold boot – (1) First software initialization of the computer. (2) Software loading and checking just after the computer has been turned on.
Collision domain – In some network technologies, such as Ethernet, “collisions” of packets are possible. A collision domain is a group of machines on a network whose packets may collide with each other. Routers and switches break up collision domains and potentially increase performance.
Color graphics adapter (CGA) – Equipment which provides 200 vertical x 600 horizontal pixel resolution for digital (rather than analog) video signals.
Column – Vertical arrangement of characters.
Common carrier – Government-regulated, private company that furnishes the general public with telecommunications services and facilities; for example, a telephone or telegraph company.
Common channel interoffice signaling (CCIS) – A method in which labeled messages convey signaling and call completion information over a single circuit, leaving other circuits free for voice, data or video transmissions. Example: Signaling System 7.
Common control switching arrangement (CCSA) – Network service that directs inward and outward dialing typically with a seven-digit code. Originally designed as a feature for private networks. Now seen in virtual switched private line networks.
Common control switching 7 (CCS7) – A digital communications channel dedicated for the processing of signaling and call setup information between processors in the switched network. (2) An international standard for network signaling via data links operating at 56 kbps. Synonym: Signaling System 7.
Common intermediate format (CIF) – The type of coded video frame transmitted when using CCITT recommendation H.261 coding methods. CIF is 30 frames per second, 325H x 288V pixels.
Communication – Transmission of intelligence between two points (origin and reception) without alteration of sequence or structure of the information content. See also data communication.
Communications outlet – The end location point for attachment of communication devices. It is typically a faceplate mounted on a wall with one or more jacks.
Communications Satellite Corporation (COMSAT) – A United States company created by an act of Congress in 1962 to provide communications via satellites. COMSAT leases satellite circuits to many American companies and is active in international communications through partial ownership in the International Telecommunications Satellite Organization (INTELSAT) and the International Maritime Satellite Organization (INMARSAT).
Communications terminal – Any device which generates or receives electrical or tone signals that can be transmitted over a communications channel.
Component video signal – Transmission in which the red (R), green (G) and blue (B) picture components are present as individual bits of information. [Synchronization information may be included with the G signal or be separate.]
Composite video signal – Transmission incorporating luminance, color and synchronizing information.
Compression – Techniques to reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory. (2) Application technique.
Continuous presence – A video processing, transmission and display mode that involves combining parts of two separate video images for transmission in a single data stream.
CompuServe – An information retrieval service which operates primarily in a videotex-like mode but also allows for standardized time-sharing as well as bibliographic and numeric retrieval. See: videotex
Computer – A device capable of solving problems or manipulating data by accepting data, performing prescribed operations on the data and supplying the results of these operations. Various types of computers are: analog computer, digital computer, calculator.
Computer-aided design (CAD) – Automation of the performance of various operations according to graphic design specifications through the use of a special computer and peripherals.
Computer-aided manufacturing (CAM) - Automation of the performance of various operations according to manufacturing specifications through the use of a special computer and peripherals.
Computer-assisted instruction (CAI) – An application in which a stand-alone personal computer or system is used to teach. Applications usually involve a dialog between students and software programs which inform students of their mistakes in a real-time manner.
Computer science – The study of computer hardware and software.
Concatenation – (1) To unite in a series; to link together; to chain. (2) The linking of transmission channels (phone lines, coaxial cable, optical fiber) end-to-end.
Conditioning – (1) To bring to a standard. (2) Addition of equipment to voice grade lines to provide for data transmissions at specified minimum values of line characteristics, in ranges from C1 to C4 (the best). [Common carriers often recommend no conditioning for lines transmitting at 1200 baud; C1 for 2400 baud, C2 for 4800 baud and C4 for speeds above 4800 baud.]
Conduit – Tubing, usually metal, through which cable is run, providing wiring for activation of voice and data lines.
Conference call – A connection established among three or more stations in such a manner that each of the stations is able to communicate with all the others.
Configuration – The interconnection and programming of independent machines or equipment to operate as a system.
Contention – Condition on a communications channel or in a peripheral device when two or more stations try to either transmit at the same time or access a resource simultaneously.
Control unit (CU) - Central processor of a telephone switching device.
Consultative Committee on International Telegraph and Telephone (CCITT) - An internationally recognized advisory group that recommends worldwide standards for common-carrier communications services.
Conversational mode – Operation of a data processing system in which a sequence of alternating entries between a user and the system takes place in a manner comparable to a conversation between two persons.
Counter - Device which tallies the number of occurrences of an event (example, a cash register) .
Country code - A one-, two- or three-digit number used for international dialing. [The first digit is always the world-zone number. Subsequent digits further define the geographic area.]
Crosstalk - Transmission noise caused by energy “leaking” from one channel to another on the same facility. [In analog voice communications, crosstalk makes conversation on one circuit accidentally audible on another.]
Current loop – Transmission technique that recognizes current flows, rather than voltage levels. [Traditionally used in teletypewriter networks, incorporating batteries as the transmission power source.]
Cursor – Position indicator frequently employed in terminals or workstations to indicate where a character is to be corrected or data is to be entered.
Customer owned and maintained (COAM) – User provided and serviced communications equipment and its associated wiring.
Customer premises equipment (CPE) – All telecommunications equipment (except pay phones) and, usually, wiring that is located at the users building.
Customer service team – A team of IT Communications Services staff who provide service to a particular U-M department. The team includes a CRM, Analyst, Engineer, etc.
Cut - (1) Transfer of a service from one facility to another. (2) Process of moving from a test environment into full production. (3) Implementation of a system in a continuous, time bound manner.
Cut through - Establish a complete path for signaling and/or audio communications.
Cyclic redundancy check - Error detection technique. [Using a polynomial, a series of two eight-bit block check characters are generated that represent the entire block of data. The block check characters are incorporated into the transmission frame, then checked at the receiving end.]
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