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
T CARRIER - AT&T's sequential letter designation for its PCM telephone carrier systems, suffixed by a number indicative of the capacity of the system.
T-1 - 24 voice channels digitized at 64,000 bps, combined into a single 1.544 mbps digital stream (8,000 bps signaling), and carried over two pairs of regular copper telephone wires. Used primarily by telephone companies until 1983. Now used for dedicated local access to long distance facilities, long-haul private lines, and for regular local service. Today, most any 1.544 Mbps digital stream is called T-1, regardless of its makeup or what the transmission medium is.
T1C - 48 voice channels digitized at 64,000 bps, combined into a single 3.152 mbps digital stream (2 x 8,000 bps signaling plus 64,000 bps framing control), for carriage over intercity "toll grade" twisted pair cable.
T-2 - 96 voice channels digitized at 64,000 bps, combined into a single 6.312 mbps digital stream (4 x 8,000 bps signaling plus 2 x 64,000 bps sub-framing plus 8,000 bps framing) is often placed on bypass microwave; this arrangement is not the original plan of Bell Labs, which expected to use a T-2 system on coaxial cable that never was built, thus "T-2" is somewhat of a misnomer.
T3 - 672 voice channels digitized at 64,000 bps, combined into a single 44.736 mbps digital stream in the form of 28 T-1's plus added framing for transmission on local fiber optic lightguide or microwave radio.
T4 - 4032 voice channels digitized at 64,000 bps, combined into a single 274.176 mbps digital stream in the form of 168 T-1's plus added plus added framing for transmission on intercity fiber optic lightguide or microwave radio.
TABLE-DRIVEN - Describes a logical computer process widespread in the operation of communications devices and networks, where a user-entered variable is matched against an array of predefined values; this is a frequently used logical process in network routing, access security and modem operation.
TAIL END HOP OFF (TEHO) - In a private network, a call carried over flat rate facilities (Intermachine Trunks or IMT) to the closest switching node to the destination of the call, and then connected into the public network as a local call.
TANDEM - 1.) General telecommunications: Connecting the output terminals of one network, circuit or link directly to the input terminals of another, as in tandem linkage of microwave relays; 2.)Specific to telephone switching: A switching arrangement in which the trunk from the calling office is connected to a trunk to the called office through an intermediate point (called a tandem exchange or tandem switch).
TANDEM DATA CIRCUIT - A data circuit relayed by connecting two DCEs back-to-back on their DTE interfaces. At the relay point, transmitted and received data, clock and other control signals must be transposed; if not accomplished in a switching system, a cable between the two must do so, often called a "rollover cable," or "null modem."
TANDEM SWITCHING SYSTEM - - Synonym: Tandem Tie Trunk Network.
TANDEM TIE TRUNK NETWORK (TTTN) - A serving arrangement which permits sequential connection of tie trunks between PBX/CENTREX locations by utilizing tandem operation.
TANDEM TRUNKING - Trunks which connect two or more switches together.
TARIFF - The published rates, regulations, and descriptions governing the provisions of communications service.
TCAM (TELECOMMUNICATIONS ACCESS METHOD) - An IBM macro language for creating communications applications programs and message control.
TELCO - Local telephone company; now properly called an LEC.
TELECOMMUNICATIONS - The transmission of voice and/or data through a medium by means of electrical impulses and includes all aspects of transmitting information.
TELEGRAPH - A system employing the interruption of, or change in, the polarity of DC current signaling to convey coded information. Many techniques of data communications follow precepts first established in telegraphy.
TELEMETRY - Technology of measuring a quantity or quantities, transmitting the results to a distant point and there interpreting, indicating or recording the quantities measured; with so many elements common to classic public communications, it can be seen to fit under the umbrella of telecommunications.
TELEPHONE - A device converting acoustical (sound) energy into electrical energy for transmission to a distant point.
TELEPROCESSING - 1.) Remote access data processing; 2.) Use of data link communications to accomplish a computer- based task; distinguished from Distributed Data Processing in that an application processor is not required at each and every node as in DDP.
TELETEX - A communications service enabling document correspondence on an automatic memory-to-memory basis over a switched public communications network; the CCITT's successor to Telex, with a transmission speed of 1200 bps using CCITT International Telegraph Alphabet #5 ... for all practical purposes, ASCII.
TELETEXT - Generic term for essentially one-way broadcast of graphics and text for display on user television sets or low cost CRT's. Many forms simply transmit frame after frame of video repeatedly and the user selects the desire frame(s) at the receiver. Rather long-established and highly evolved in Europe, all North American efforts have been rather ineffective to date, with a number of commercial failures. Typical transmission medium is as a data signal hidden in the blank space of broadcast television vertical synchronizing pulses, although other means are possible on TV broadcast signals as well. Videotex is the interactive form of Teletext (which also see).
TELETYPEWRITER - A machine used to transmit and/or receive communications on printed page and/or tape.
TELETYPEWRITER EXCHANGE SERVICE (TWX) - Originally an AT&T communications service product, now the property of Western Union Corporation under the product name Telex II, transmitting ASCII code at 110 bps; interfaced to a number of other services of different codes and speeds through a mainframe-based protocol converter Western Union calls InfoMaster.
TELEX - The CCITT's global teleprinter exchange switched service based on 50 bps transmission of Baudot code. While archaic in view of recent advances, Telex remains the most conveniently widespread telecommunications service to any corner of the world, reaching more places than the telephone.
TERMINAL - 1.) A point at which information can enter or leave a communications network; 2.) Any device capable of sending or receiving information over a communications channel.
TERMINAL EQUIPMENT - Devices, apparatus and their associated interfaces used to forward information to a local customer or distant terminal.
TERMINATION - 1.) An item that is connected to the terminal of a circuit or equipment. 2.) An impedance connected to the end of a circuit being tested. 3.) The points on a switching network to which a trunk or line may be attached. 4.) The end time or end point of a contract for communications services.
THROUGHPUT - A widely varying measurement of the number of bits, blocks, characters, messages or interactive transactions passing though a data communications system. Measurement methods are highly variable and subject to many influences that must be identified in order to obtain a meaningful assessment.
TIE-LINE/TIE LINE/TIELINE - A private leased line linking two phones or phone systems directly. Can ring distant phone automatically when telephone is lifted from its mounting (ARD), when a short code is dialed (OPX), or may relay random calls between two switching machines (DRTL).
TIME DIVISION MULTIPLE ACCESS (TDMA) - a satellite communications technique for sharing use of a satellite transponder by dynamically allocating time slots among its users, under control of a common signaling channel; has many technical commonalities with a land-based "common channel signaling system" for telephony.
TIME DIVISION MULTIPLEXING (TDM) - Equipment enabling transmission of a number of independent signals over a common path by transmitting them sequentially at different instants of time.
TIME-DIVISION SIGNALING - In TDMs, use of a common signaling channel time slot for the telephone supervisory signaling of all telephone channels borne on the TDM link.
TIME-DIVISION SWITCHING - Switching method used by assigning the data entering one port at one end of a data stream to a different port at the other end; used in both electronic telephone exchanges an so-called "switching TDMs."
TIME-SHARING - The sharing of use of a processor among multiple simultaneous users; often using telecommunications to connect users at a distance.
TIME-OUT/TIMEOUT/TIME OUT - A technique used throughout telecommunications to cause an action to default to a preset course, alarm a failure, or control traffic loads. Essentially amounts to placing a timer in the path to run its course, initiating an action if it reaches the end of its time; otherwise resetting the timer and holding it off.
TOKEN PASSING - A LAN access method in which a "token" message constantly circulates around the network, inviting users to attach their messages for transmission; first developed by Eric Soderblom of Sweden. A station may not transmit unless it has the token, meaning the medium is clear for transmission. While most commonly associated with IBM's ring topology LANs, can be applied to any topology.
TOLL CALL - Any call to a point outside the user's immediate local calling area.
TOLL CENTER - 1.) A central office where operators (human or mechanical) are present to assist in completing incoming toll calls. 2.) Name of a Class 4 switching center in the original Bell DDD hierarchy of long distance switching centers, providing links to the local exchanges of a city or metropolitan area; the point of interconnection between local networks and intercity networks.
TOLL OFFICE - A center for the switching of toll calls and the termination of intercity transmission facilities.
TOLL PLANT - The facilities that connect toll offices throughout the country.
TOLL RESTRICTION - A restriction in outgoing trunks which counts the first three digits dialed and diverts calls to forbidden codes either to a busy tone, to the operator, or to a recorded announcement.
TOP (TECHNICAL OFFICE PROTOCOL) - General Motors' data protocol optimized for use on LANs serving engineering offices, with their typically long graphics file transfers. Contrast: MAP.
TOPOLOGY - The logical or physical arrangement of nodes on a network in relation to each other; common terms are ring, star, bus and tree.
TOUCH-TONE ADAPTOR - A device that can be connected to a rotary dial telephone to allow for DTMF signaling.
TRACE PACKET - A special test packet in packet networks that causes a report to be sent back to the network control center from each node it transits in its path through the network.
TRAFFIC - Calls being sent and received over a communications network.
TRAFFIC MEASUREMENT AND RECORDING SYSTEMS (TMRS) - A computer generated report showing usage information of telephone systems. Usually this includes trunk utilization, outages, queuing time, and the need for additional common equipment.
TRAFFIC SERVICE POSITION SYSTEM (TSPS) - A toll switchboard position configured as a push button console.
TRANSCODER - A digital device converting the coding of one system to another; most common is the T-1/CEPT conversion of 1.544 megabit T-1 streams to 2.048 CCITT digital carrier streams.
TRANSMISSION - The electrical transfer of a signal, message or other form of information from one location to another; most desirably in unaffected form at the receiver.
TRANSMISSION LEVEL - In telephony, the level of power of a signal, (at 1,000 Hertz in North American practice; 800 Hertz globally), which should be measured at a particular reference point.
TRANSMISSION SPEED - Number of pulses or bits transmitted in a given period of time, expressed variably in Bits Per Second (BPS), Words Per Minute (WPM), Characters per Second (CPM), an occasionally as Lines per Minute (LPM) in printer transmission. Skilled technologists can translate one to the other.
TRANSPARENCY ("TRANSPARENT COMMUNICATIONS") - 1.) A basic objective of telecommunications systems, to make the transportation of information invisible to the user; 2.) In data communications, a suspension of control character recognition in certain systems while information transfer is in progress.
TRANSPONDER - 1.) Generally, a telecommunications device that receives a signal in one form and relays it out in another form; 2.) In satellite communications, the prime function aboard a satellite that receives signals on one microwave channel an retransmits them on another; many satellites have 24 to 36 transponders on board.
TRANSPORT LAYER - The fourth layer of the ISO Open Systems Interconnection Reference Model; performs the function of end-to-end control of transmitted information and is responsible for optimized use of network resources, implying a parallel to switched telephony routing control resides here.
TREE - a bus network topology in which branches feed off the bus at various points; closely akin to multipoint lines in telephony; - Synonym: Branching Bus (archaic).
TRUNK - A telephone circuit or path between two switches, at least one of which is usually a telephone company Central Office or switching center. Regular local CO circuits are called PBX trunks, because there is a switch at both ends of the circuit.
TRUNK GROUP - An group of telecommunications switched channels between two locations; the physical path of all may be variable, so long as the logical path is the same.
TRUNK TYPE (TT) - Trunks that use the same type of circuit operation between the same terminating locations.
TRUNK UTILIZATION REPORT (TUR) - A computer printout detailing the traffic use of a trunk.
TSO (TIME SHARING OPTION) - An archaic IBM environment for implementing time-shared use of a mainframe computer; operates under IBM's obsolescent OS-based operating system.
TTL (Transistor-to-Transistor Logic) - An internal transfer standard for electronics devices in which a 1 state is +5 Volts and a zero state is ) volts; communications systems are sometimes expected to interface to this and provide transmission converters to telecommunications standards.
TTY (TELETYPE) - 1.) The registered trade name for teleprinters and data terminals of the Teletype Corporation; 2.) Used generically in the telecommunications industry for teleprinters or data terminals that emulate teleprinter operations.
TURNAROUND TIME - 1.) Time required to reverse the direction on a half-duplex communications channel; 2.) Somewhat misapplied if used in data communications to describe the total response time, including processor time, for interactive data transactions.
TWO-WIRE CIRCUIT - (1) A channel for transmitting data in one direction at a time. (2) A short distance channel using a single send/receive pathway, usually a twisted pair of wires, connecting a telephone to a switch. Implies half-duplex communications operations.
TELETYPEWRITER EXCHANGE SERVICE (TWX) - A service whereby a customer's leased teletypewriter is connected to a "TWX" switching exchange; thence to a teletypewriter of any customer who subscribes to a similar service. Originally AT&T's equivalent to Telex, TWX is now owned by Western Union and sold under their product name Telex II. Interconnection from and to TWX an Telex with a wide variety of telecommunications services is available on-line via carrier-provided protocol conversion. TWX operation as a PSN is available in North America only; Telex is the global equivalent.